The Complete Handbook for Producers and Hobbyists Growing nuts is not only gaining popularity with commercial producers, there is now significant interest from small property farmers and home gardeners as well.
The Nut Grower’s Guide contains essential information for growers and producers of all tree nuts, farmers looking to diversify and also for gardeners interested in growing nut trees in their back yard.
Jennifer Wilkinson has been involved in nut growing since in the 1970s when she began planting walnut trees in East Gippsland, Victoria. Her interest in other tree nuts soon expanded and in 1996 she became editor of Australia’s only nut journal, Australian Nutgrower, published by the Australian Nut Industry Council. As editor, Jennifer has travelled to nut orchards, processing facilities and research institutions in all states and New Zealand and she regularly liases with growers, processors, nurseries and researchers working on nut industry projects. She is a recognised authority in the industry and is keenly sought after by those who are planning to grow nuts commercially or are seeking information about growing nut trees as a hobby.
Jennifer Wilkinson
This is the first comprehensive handbook to cover all relevant aspects for almonds, cashews, chestnuts, hazelnuts, macadamias, pecans, pistachios, and walnuts. Detailed material is presented on site selection, from soil and climate to aspect and topography through to previous land use and local pest species. Soil preparation, irrigation, planting and propagating trees are also covered. It also deals with the cultivation and processing of each of the major nut species and also provides guidance on packaging and the wholesale and retail marketing of nuts in Australia and overseas.
About the author
Nut Grower’s Guide
Nut Grower’s Guide
Jennifer Wilkinson
Nut Grower’s Guide The Complete Handbook for Producers and Hobbyists
Nut Grower’s Guide
Nut Grower’s Guide The Complete Handbook for Producers and Hobbyists
Jennifer Wilkinson
© Jennifer Wilkinson 2005 All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact Landlinks Press for all permission requests. National Library of Australia Cataloguing-in-Publication entry Wilkinson, Jennifer, 1949–. Nut grower’s guide : the complete handbook for producers and hobbyists. Includes index. ISBN 0 643 06963 1. 1. Nuts – Australia. 2. Nut trees – Australia. 3. Nut industry – Australia. I. Title. 634.5 Published by and available from Landlinks Press 150 Oxford Street (PO Box 1139) Collingwood VIC 3066 Australia Telephone: +61 3 9662 7666 Local call: 1300 788 000 (Australia only) Fax: +61 3 9662 7555 Email:
[email protected] Website: www.landlinks.com Landlinks Press is an imprint of CSIRO PUBLISHING Front cover photos by the author except for Macadamia hedging photo by D. Huett. All drawings and photos included in the text by the author unless stated otherwise. Set in 10.5pt Minion Cover design by Jo Waite Design Typeset by J & M Typesetting Printed in Australia by BPA Print Group
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Acknowledgments
Firstly I would like to thank the many nut growers, nut processors and researchers for sharing their experiences and technical knowledge with me. In particular I would like to thank the following nut industry people who answered my questions when I was researching this book and also offered words of wisdom on the specific nut chapters: Chris Bennett and Peter Freeman for their help on almonds; Peter Shearer and Patrick O’Farrell for their help with cashews; Jane Casey and Joe Rinaudo for their help with chestnuts; Basil Baldwin and Peter Wheelwright for their help with hazelnuts; Kim Jones, Andrew Heap and Graeme Hargreaves for their help with macadamias; Jon Craven, James Payne and Ross Loebel for their help with pecans; Chris Joyce and Cathy Taylor for their help with pistachios; and Leigh Titmus and Harold Adem for their help with walnuts. Thank you too to Alan Broughton and Robyn Grant for their help with organic agriculture, and to Russell Needham for his help with the business side of growing nuts. I would also like to thank CSIRO Publishing, Briana Elwood and Ted Hamilton in particular, for publishing this book and for their professional expertise and personal support. Of course no book can be written without significant support from family and friends. To all my family, thank you for your patience and encouragement, and a special thank you to my husband Norm for his constructive criticism, technical advice, meticulous editing and for all the cups of tea and coffee and words of encouragement brought to me at the computer.
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Foreword
As a grower of macadamia nuts and as an officer in other activities of the tree nut industry in Australia I find it very refreshing to see a book published that is able to deal successfully with horticultural practices for all the different tree nuts under the one cover. Tree nut growers are experiencing a very strong growth in the demand for their product. This is occurring as a result of scientific evidence proving that tree nuts are an important part of a person’s diet. In Australia there is a general shortage of home-grown tree nuts, consequently there is quite a large quantity of tree nuts imported to satisfy this consumer demand. There is an opportunity for our industries to increase the amount of home-grown product. Jennifer has created a book that is right on the mark. It tells us the best ways to grow tree nuts in the Australian environments. It provides the reader with just enough information to make the individual a very good grower; there is not a wasted word. Irrigation and nutrient detail is completely up to date. The amount of detail written into each chapter and the order of its importance will give the reader plenty of incentive to seek out further knowledge. This is a ‘hands-on’ book. Jennifer has identified all the important ingredients necessary to become a good grower of tree nuts. The reader can be confident that the detail written into her book will be adequate to grow a product that will meet the stringent quality standards that the Australian consumer expects of their home grown products. Good growing to all. Phil Montgomery President Australian Nut Industry Council Ltd March 2005
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Contents
Acknowledgments
v
Foreword
vi
Introduction
ix
Chapter 1
What’s in a nut?
1
Chapter 2
Nut production worldwide
9
Chapter 3
What nut grows where
15
Chapter 4
Propagation
21
Chapter 5
Planting a nut orchard
29
Chapter 6
Managing a nut orchard
39
Chapter 7
Organic nut production
61
Chapter 8
Success in business
71
Chapter 9
Almonds
81
Chapter 10
Cashews
99
Chapter 11
Chestnuts
109
Chapter 12
Hazelnuts
125
Chapter 13
Macadamias
141
Chapter 14
Pecans
157
Chapter 15
Pistachios
175
Chapter 16
Walnuts
189
Chapter 17
Other tree nuts
211
Appendix 1
Nut tree notes for gardeners
219
Index
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Introduction
It is no secret that nuts have been a valued food since prehistoric times. Nut harvest was a time of ceremony for hunter-gatherers, and today nuts continue to be considered gourmet food. In fact, consumption of nuts and nut products is increasing and medical authorities are recommending more nuts in the diet for health reasons. This is very good news for nut growers. Nut production in Australia has increased significantly over the past two decades. The size of nut orchards has also increased. Yet while the greater efficiency of large orchards and the positive market situation has generated interest from investors, the majority of nut orchards continue to be run as family businesses. In addition, many orchards are an important part of ‘lifestyle farming’ and provide loads of fun and satisfaction for weekend and semi-retired farmers. Of the eight tree nut crops grown commercially in Australia, production volumes of four of these crops (almonds, macadamias, pecans and pistachios) is substantial and supported by modern processing and marketing facilities. Production of the other four nut crops is increasing at varying rates. Chestnut production has been relatively static for some years but production is now set to increase as chestnut processing opportunities are developed. Walnut production has also remained reasonably static over the past few decades but crops from large new orchards have boosted recent production and a rapid increase is expected within the next few years. It is expected that development of highcapacity walnut processing facilities will follow. Cashew production has been investigated since the 1960s but the difficulty in processing cashew product has thwarted development. At this stage cashew production is limited to one commercial grower with a few other plantations on the horizon. Hazelnuts have been grown widely in Australia for many decades on small-scale orchards, but larger plantings are being developed and the hazelnut industry is looking toward a positive future. Different tree nuts are grown in different climates, from the tropics to cool temperate zones. Each nut type has a particular set of cultural requirements and processing and marketing systems. So what are these requirements and which nut grows best where? The information in this book comes from a combination of first hand experience, personal communication with others involved in the nut industries, and literary research. As editor of Australia’s only nut industry journal for almost ten years, my knowledge of nut production increases with each issue that is published. Similarly, as a walnut grower, my knowledge of walnut cultivation and processing is fine-tuned as each season passes. It is thirty years since my husband and I planted our first walnut trees and in that time there have been huge technical changes to walnut cultivation. Perhaps the greatest
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x
Nu t Gr o w e r ’s G uide
change was brought about with the introduction of lateral bearing cultivars from California. No longer were walnut trees managed as large individuals because lateralbearing cultivars can be planted as in other high density orchards. The result has been greater yields per hectare and greater efficiency in orchard management. The changing walnut scene is typical of other types of tree nuts. As with most forms of farming, the never-ending discoveries about the nut trees that you grow, and observing the results of new techniques you try, makes nut production an absorbing and stimulating occupation. Each new season provides a new opportunity to do better than what you did last year. The eternal quest of every grower is, or should be, to produce high quality nuts in the most efficient and most sustainable manner possible. To achieve this to one’s satisfaction may take a lifetime, but what a challenging life it will be.
Large chestnut trees provide dense shade in summer
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1 What’s in a nut?
Nuts are amazing little packages. They taste delicious, they’re one of the most nutritious foods available and dried nuts can be stored without refrigeration. No wonder they became a favoured food by hunter-gatherers and remain a gourmet food today. From a botanical point of view a nut can be defined as a hard-shelled fruit, or a seed containing an edible kernel. Peanuts are not true nuts; they are a type of legume. There are numerous different types of nuts grown around the world, however, the tree nuts grown in Australia are the focus of this book. Tree nuts include almonds, Brazil nuts, cashews, chestnuts, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts. Nuts that fall from the tree will germinate when planted and the concentrated food reserves within the kernel sustain the young growing plant. This concentrated food reserve provides a rich source of nutrients in the human diet. These nutrients include fats, proteins, carbohydrates and fibre, and also vitamins, minerals and phytochemicals.
The health benefits of nuts Scientific evidence on the health benefits of nuts has been accumulating for many years as scientific institutions around the world research the properties of nuts and their benefits to human health. In 2003 the Australian Nut Industry Council Ltd launched the ‘Nuts for Life’ program to compile existing information on the health benefits of nuts and communicate this information to health authorities and health professionals. Scientific research shows that eating nuts regularly is beneficial to health. For instance, four major epidemiological studies have shown that frequent nut consumption confers protection against coronary heart disease, with a level of risk reduction of up to 53% in those eating nuts five or more times a week compared with people eating nuts twice a week or less1–4. The cardiovascular benefits of nuts have been attributed to their
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favourable fatty acid profile along with their vitamin E, antioxidants, folate, arginine and phytosterol content. Epidemiological studies show consumption of tree nuts is associated with a lower risk of prostate cancer5 while in vitro and animal studies show potential anti-cancer properties in certain components of tree nuts6,7. A recent epidemiological study showed that women who ate nuts five or more times a week had 27% lower risk of developing diabetes compared with women who ate nuts twice a week or less8. While at present not all tree nuts have been glycemic index tested, pecans and cashews which have been tested have a low glycemic index. Tree nuts also provide monounsaturated fatty acids and contain dietary fibre — all nutritional attributes that assist with optimal glycemic control. Tree nuts are also a source of the amino acid arginine that has been shown to improve insulin sensitivity and reduce the risk of complications in people with diabetes. Research also shows that higher protein, moderate fat diets may be more effective for weight loss than high carbohydrate, low fat diets due to their beneficial effects on satiety, improved metabolic parametres and an increase in the thermogenic component of the metabolic rate9, 10. Unfortunately, a small percentage of the population have an allergy to nuts. Health officials have reported that the incidence of nut allergies is increasing. Severe reactions (anaphylaxis) can result in death if not treated immediately. Peanut allergies affect 2% of children in the preschool age group and 60% of these children will also have an allergy to a nut other than peanuts. As a result of the increasing incidence of nut allergies in Australia, nuts are becoming a prohibited food for young children at childcare centres and primary schools. It is reported that the processes of maturation, roasting and curing, that increase flavour and shelf life of peanuts, all increase their allergenic properties. These processes are also likely to be important in modifying the allergenic properties of other nuts (Soutter 2004).
What are the healthy substances in nuts? The following information has been sourced from scientific studies conducted worldwide. These studies are summarised in the Fact Sheets published by Nuts for Life, an initiative of the Australian Nut Industry, Copyright 2003, Horticulture Australia Limited.
Oils Nuts are a great source of healthy oils. These are the oils that are high in monounsaturated or polyunsaturated fats. Nuts high in monounsaturated fats include macadamias, cashews, almonds, pistachios and pecans. Nuts that are high in polyunsaturated fats include walnuts, hazelnuts, pine nuts and Brazil nuts.
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W h a t ’s i n a n u t ?
3
Low glycemic index Pecans and cashews have a low glycemic index (GI), meaning that the carbohydrate they contain is broken down slowly by the body. The GI of other tree nuts is yet to be tested. Low GI foods assist in the management of weight, blood glucose levels and cholesterol.
Fibre All nuts contribute fibre to the diet. Dietary fibre helps to lower blood cholesterol and is essential for healthy bowel function.
Vitamin E Vitamin E is an antioxidant that helps protect tissues in the body from damage.
Folate Folate is a B vitamin associated with heart health, cancer prevention and decreases the risk of birth defects in babies.
Magnesium Magnesium is a mineral essential for good nerve and muscle function and for strong bones.
Zinc Zinc is needed for many processes in the body and is necessary for a strong immune system and healing and protecting the skin.
Selenium Selenium is essential for a well functioning immune system and thyroid gland. It also helps protect body cells from damage.
Antioxidants Antioxidants found in nuts include flavonoids and a compound called luteolin. These substances help slow down the aging process and help protect the body from a range of lifestyle related diseases.
Arginine Arginine is an amino acid that helps keep blood vessels healthy.
Plant sterols Nuts contain plant sterols that are substances that reduce cholesterol absorption.
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Table 1. Nutritional analysis of raw tree nuts Data obtained from AusNut, Foodworks version 3.01, Xyrus Software unless otherwise indicated. na, not available; nt, not tested. Kilojoule content includes the energy from dietary fibre. Per 100 g
Almond
Brazil
Cashew
Chestnut3
Hazelnut
Energy Kj
2525
2888
2437
797
2693
Protein (g)
20.0
14.4
17.0
3.4
14.8
Total fat (g)
55.2
68.5
49.2
0.6
61.4
Saturated fat (g)
3.6
14.8
8.4
nt
2.7
Monounsaturated fat (g)
36
21.8
31.1
nt
48.6
13.1
29.0
7.5
nt
7.1
0
0
0
nt
100
Total CHO (g)
4.4
2.4
16.8
34.3
5.1
CHO sugars (g)
4.4
2.1
5.5
3.8
4.4
Dietary fibre (g)
8.8
8.5
5.9
8.1
10.4
Sodium (mg)
5.0
2.0
11.0
0.7
3.0
Potassium (mg)
690
560
550
574
680
Magnesium
260
350
250
nt
160
Calcium (mg)
235
150
34.0
13.4
86.0
Iron (mg)
3.5
2.2
5.0
0.8
3.2
Zinc (mg)
3.6
4.1
5.5
0.5
2.2
Thiamin (mg)
0.17
0.60
0.64
0.28
0.39
Riboflavin (mg)
1.15
0.43
0.19
0.09
0.17
Niacin (mg)
3.80
0.60
1.80
1.97
2.20
Folate (µg)
49
21
68
<0.1
72
Pantothenic acid (mg)2
0.349
0.236
0.864
0.56*
0.918
Vitamin B6 (mg)2
0.131
0.251
0.417
0.5*
0.563
Vitamin A (µgRE)
2.0
2.0
1.0
1.0*
3.0
Vitamin E (mg)2
26.2
7.6
1.5
0.5*
15.2
Copper (mg) 2
1.11
1.77
2.19
0.51*
1.72
Manganese (mg)2
2.53
0.77
1.65
1.18*
6.17
Selenium (µg)2
4.4
2960
20
1.12*
4.0
Arginine (g)2
2.47
2.39
1.74
0.23*
2.21
Phytosterols (mg)2
120
na
158
na
96
Polyunsaturated fat (g) Omega-3 fat
1 2 3 4
(mg)1
Meyer et al. (1999) USA Department of Agriculture Nutrient Database for Standard Reference Release 15. Australia data for dry roasted chestnuts, *USDA data for raw peeled European chestnuts. Average quantities excluding nuts with unavailable data
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W h a t ’s i n a n u t ?
Table 1. Nutritional analysis of raw tree nuts (cont.)
Macadamia
Pecan
Pine nuts
Pistachio
Walnut
Mixed tree nuts4
3068
2977
2921
2530
2901
2574
7.6
9.8
13.0
19.7
14.4
13.4
76.2
71.9
70.0
50.6
69.2
57.34
10.3
4.5
4.2
5.8
4.4
6.5
61.4
39.1
23.0
26.6
12.1
33.3
0.9
24.8
39.8
15.8
49.4
20.8
0
600
0
0
6300
778
4.5
4.9
4.5
15.1
3.0
9.5
4.5
4.3
3.4
5.9
2.7
4.1
6.0
8.4
5.1
9.0
6.4
7.7
3.0
3.0
3.0
7.0
3.0
4.1
330
500
600
950
440
587
Nut Growers.indd 5
95
110
230
100
150
160.6
48.0
51.0
11.0
90.0
89.0
80.7
1.8
2.4
4.1
3.9
2.5
2.9
1.2
3.9
5.3
2.3
2.5
3.1
0.28
0.42
0.57
0.58
0.33
0.43
0.10
0.18
0.19
0.29
0.18
0.30
2.00
1.30
4.30
1.50
1.40
2.09
16
39
60
67
66
56.8
0.758
0.863
0.210
0.520
0.570
0.585
0.275
0.210
0.111
1.700
0.537
0.470
0
4.0
2.0
22.0
4.0
4.1
0.5
4.1
na
4.6
2.9
7.0
0.75
1.20
1.04
1.30
1.58
1.32
4.13
4.50
4.33
1.20
3.41
2.99
4
6
na
7
5
335
1.38
1.18
2.25
2.13
2.28
1.83
114
102
na
214
72
125
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Nu t Gr o w e r ’s G uide
References 1. Kushi, L. H., Folsom, A. R., Prineas, R. J., Mink, P. J., Wu Y., and Bostick, R. M. (1996). Dietary antioxidant vitamin and death from coronary heart disease in postmenopausal women. New England Journal of Medicine 34, 1156–1162. 2. Hu, F. B., and Stampfer, M. J. (1998). Nut consumption and risk of coronary heart disease: a review of epidemiologic evidence. Current Athero Reports 1, 205–210. 3. Albert, C. M., Gaziano, M. J., Willet, W. C., and Manson, J. E. (2002). Nut consumption and decreased risk of sudden cardiac death in the Physicians’ Health Study. Archives of International Medicine 162, 1382–1387. 4. Fraser, G. E., Sabate, J., Beeson, W. L., and Strahan, T. M. (1992). A possible protective effect of nut consumption on risk of coronary heart disease. The Adventist Health Study. Archives of International Medicine 152, 1416–1424. 5. Jain, M. G., Hislop, G. T., Howe, G. R., and Ghadirian, P. (1996). Plant foods, antioxidants, and prostate cancer risk: findings from case-control studies in Canada. Nutrition and Cancer 34(2), 178–184. 6. Ip, C., and Lisk, D. J. (1994). Bioactivity of selenium from Brazil nut for cancer prevention and selenoenzyme maintenance. Nutrition and Cancer 1(3), 203–212. 7. Narayanan, B. A., Geoffroy, O., Willingham, M. C., Re, G. G., and Nixon, D. W. (1999). p53/p21WAF1/CIP1 expression and its possible role in G1 arrest and apoptosis in ellagic acid treated cancer cells. Cancer Letters 136(2), 215–221. 8. Jiang, R., Monson J. E., Stampfer J. J., Liu S., Willett W. C., and Hu, F. B. (2002). Nut and peanut butter consumption and risk of Type 2 diabetes in women. Journal of the American Medical Association 288, 2554–2560. 9. Eisenstein, J., Roberts S. B., Dallal, G., and Saltzman, E. (2002). High-protein weightloss diets: are they safe and do they work? A review of the experimental and epidemiologic data. Nutrition Review 60(7), 189–200. 10. McManus, K., Antinoro, L., and Sacks, F. (2001). A randomised controlled trial of a moderate-fat, low-energy diet compared with a low fat, low-energy diet for weight loss in overweight adults. International Journal of Obesity 5, 1503–1511.
Further reading Australian Nut Industry Council Ltd website http://www.nutindustry.org.au Boutrif, E. (2000). Minimising mycotoxin risks. Australian Nutgrower 14(1), 11–13. Cowart, G. (2003). Nuts for health program launched. Australian Nutgrower 17(2), 3. Hasler, C. M., Kundrat S., and Wool, D. (2001). Studies prove nuts a functional food. Australian Nutgrower 15(4), 24. International Nut Council (2000). Nut research shows health benefits of nuts. Australian Nutgrower 14(3), 39. International Tree Nut Council website http://www.nuthealth.org Joyce, C. (2003). Nuts for health campaign. Australian Nutgrower 17(1). Meyer, B. J., Tsivis, E., Howe, P. R. C., Tapsell, L., and Calvert, G. D. (1999). Polyunsaturated fatty acid content of foods: differentiation between long and short chain Omega-3 fatty acids. Food Australia 51(3), 81–95.
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Nunez, I., Perez-Heras, A., Serra, M., Gilabert, R., Casals, E., and Deulofeu, R. L. (2004). New study of walnuts – cardio-protective effect beyond cholesterol-lowering. Australian Nutgrower, 18(3), 39. Nuts for Life (2003). Fact Sheet 1. ‘Nuts and General Health.’ (Horticulture Australia Ltd: Sydney, NSW.) Nuts for Life website http://www.nutsforlife.com.au Savage, G. P. (2000). The Nutritive value and composition of nuts commonly eaten by humans. Research Project, Food Group. (Lincoln University: Canterbury, New Zealand.) Somerset, S. (2000). Mediterranean diet versus low fat diet. In ‘Proceedings of the Australian Nutgrowers Conference’. p. 38. (Australian Nut Industry Council Ltd: Lismore, NSW.) Soutter, V. (2004). Allergic reactions to nuts. Australian Nutgrower 18(3), 38. Spiller, G. (1999). ‘Healthy Nuts’. (Avery Publishing Group: New York, USA.) Walker, R. (2003). Is it all a big fat lie? In ‘Proceedings of the Australian Nutgrowers Conference’. pp. 29–32. (Australian Nut Industry Council Ltd: Lismore, NSW.)
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2 Nut production worldwide
World production The natural habitat of the different nut trees extends from tropical forests to inland deserts. However, the trees are successfully cultivated in other regions having similar environmental conditions. For instance, macadamias are native to subtropical and tropical parts of New South Wales and Queensland and grown commercially in these areas, but they are also grown in other subtropical regions in Hawaii, South Africa, Central America and parts of southern Asia.
Major producing countries Almonds Afghanistan, Australia, Chile, Greece, Iran, Israel, Italy, Morocco, Portugal, Spain, Tunisia, Turkey, USA.
Cashew Brazil, China, India, Indonesia, Guinea Bassau, Kenya, Mozambique, Nigeria, Tanzania, Thailand, Vietnam.
Chestnut China, France, Greece, Hungary, Japan, Korea, Portugal, Spain. Newer producing countries are Australia, Chile and New Zealand.
Hazelnut France, Greece, Italy, Russia, Spain, Turkey, USA.
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Nu t Gr o w e r ’s G uide
Macadamia Australia, Brazil, Costa Rica, Guatemala, Israel, Malawi, South Africa, Thailand, USA (Hawaii).
Pecan Australia, Israel, Mexico, South Africa, USA.
Pine nuts China, Italy, Lebanon, Portugal, Spain, Turkey.
Pistachio Greece, Iran, Italy, Syria, Turkey, USA.
Walnut Argentina, Chile, China, France, Greece, Hungary, India, Iran, Italy, Maldova, North Korea, Turkey, Ukraine, USA.
Nut production in Australia While production of tree nuts in Australia is small on the world scale, Australia is the world’s leading producer of macadamia. Australian almond production is increasing in significance and this trend is set to continue due to the development of extensive new orchards. Plantings of most other tree nuts have also increased in Australia in the last decade. Almond production today is concentrated along the Murray River throughout the Riverland region in South Australia and the Sunraysia area of northern Victoria and the Riverina in southern New South Wales. The main production centres are: Waikerie and Renmark in South Australia, and Mildura, Nangiloc, Robinvale and Boundary Bend in Victoria. Almond orchards are also located north of Adelaide in South Australia and near Finley, Darlington Point and Moree in New South Wales. In 2004 Australia produced some 10 300 tonnes of almond kernel and the almond industry expects this to double to 20 000 tonnes of kernel within the next four years. High-tech almond processing facilities are located in the main growing areas. Cashew production is confined to one plantation in northern Queensland, Cashews Australia. The harvested crop is shipped overseas for hand-cracking. Production in 2004 totalled 300 tonnes of nut-in-shell. Chestnut production is concentrated in north-eastern Victoria and currently 70–75% of the national crop is produced in this region. Other areas of production include: southwestern Western Australia; the Dandenongs east of Melbourne; around Daylesford in Central Victoria; near Batlow, Orange and Sassafras in New South Wales, and the Adelaide Hills in South Australia. Chestnut orchards have also recently been planted near Armidale in northern New South Wales. Australia currently produces some 12 000 tonnes of fresh chestnuts annually and the industry predicts that production will increase substantially in the next few years.
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N u t p r od u c t i on wor l d wi d e
11
The main hazelnut producing areas are the Central Tablelands of New South Wales and north-eastern Victoria. Hazelnut orchards are also located in the Dandenong ranges east of Melbourne and in Tasmania. While current production is around 20 tonnes of nut-in-shell, new orchards are being planted and production is expected to steadily increase. The major macadamia producing areas are located in central and southern Queensland, including the Sunshine Coast, Atherton Tablelands, the Rockhampton and Bundaberg regions, and the mid-north coast of New South Wales, and Western Australia. Australian production in 2004 totalled 40 000 tonnes of nut-in-shell, and of this, some 8000 tonnes of kernel was exported. Several large processing facilities have been established in the major macadamia growing regions. The bulk of Australian pecans are produced by Stahmann Farms ‘Trawalla’, which is located near Moree in New South Wales. However, there are numerous other pecan orchards located from the Hunter Valley and Nelsons Bay north of Sydney to the midnorth coast near Kempsey and northern coastal New South Wales. In Queensland, pecan orchards are located at Munduberra, Gympie, the Atherton Tablelands and Beaudesert. Production in 2004 totalled close to 3000 tonnes of nut-in-shell. Pistachio production is concentrated along the Murray River from Loxton to Swan Hill, taking in the Riverland in South Australia and the Sunraysia region of northern Victoria and southern New South Wales. Additional orchards are located in western Victoria at Pinaroo and central Victoria and south-western Western Australia. The bulk of the pistachio crop is processed by Australian Pioneer Pistachio Company at Robinvale in northern Victoria. Production in 2004 totalled some 1200 tonnes of nut-in-shell.
Australia leads the world in macadamia production.
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Nut Gr o w e r’s G u i d e
In recent years, the main walnut production areas have been: the east coast of Tasmania; the Goulburn Valley near Shepparton; central Victoria; the Murray Irrigation Area in northern Victoria and South Australia; the Blue Mountains in New South Wales; the Murrimbidgee Irrigation Area near Griffith in New South Wales, and eastern and north-eastern Victoria. Production in 2004 totalled about 400 tonnes of nut-in-shell. Main almond producing areas 1 – Renmark 2 – Adelaide 3 – Robinvale, Boundary Bend, Swan Hill 4 – Finley 5 – Waikerie
1
5 2
Main cashew producing areas 1 – Dimbulah 2 – Wildman River
3
4
2 1
Main chestnut producing areas 1 – Dandenongs 2 – North-east Victoria 3 – Central Victoria 4 – Bathurst/Orange 5 – Batlow 6 – Adelaide Hills 7 – Manjimup
7
6
4 3
5
1 2
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Nut production worldwide
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Main hazelnut producing areas 1 – Orange/Bathurst 2 – North-east Victoria 3 – Gippsland 4 – Dandenongs 5 – Hobart
1 4 2 3
5
Main macadamia producing areas 1 – Atherton Tablelands 2 – Rockhampton 3 – Bundaberg 4 – Sunshine Coast 5 – Far north coast NSW 6 – Mid-north coast NSW
1 2 3 4 5 6
Main pecan producing areas 1 – Gatton, Beaudesert 2 – Lismore, north coast NSW 3 – Moree 4 – Mid-north coast NSW 5 – Hunter Valley, Nelsons Bay 6 – Gympie, Mundubbera
6 1 2 5
3 4
The main nut producing areas in Australia.
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Nu t Gr o w e r ’s G uide
Further reading Australian Nut Industry Council website http://www.nutindustry.org.au Horticulture Australia website http://www.horticulture.com.au International Tree Nut Council website http://www.treenuts.org
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3 What nut grows where?
Whether looking for land upon which to grow a particular nut, or looking for a suitable nut crop for your farm there are numerous things to consider. Detailed requirements for production of each type of nut are given in the specific nut chapters. A short list of the general factors to consider when assessing the suitability of a location for growing nuts follows.
Climate Suitable climatic conditions for each type of nut vary from tropical to cool temperate. One of the best ways of finding out where a particular nut grows well is to find out where the different nuts are grown. Travelling to nut orchards and talking to the growers about the climate and how it affects nut production is highly informative. Generally, if a nut crop is popular in a particular region the conditions in that region are suitable for that nut. Simply knowing the particular weather data for temperature and rainfall is not sufficient. When introducing a nut crop to a new area, assessment must be extremely thorough. Factors to consider in assessing the climatic suitability of a location for nut production include:
Temperature range Research all weather data recorded for the particular area, noting seasonal temperature extremes. While some nuts such as cashews, pecans and macadamias require long hot summers, other nuts such as walnuts can be damaged by sunburn in very hot conditions. Winter temperatures are also very important because deciduous nut trees require a certain amount of chilling to ripen the fruiting wood, while other nut trees, such macadamia, can be damaged by frost. Within each nut type too, some cultivars may suit a particular location while others do not. For instance, where there are late frosts in spring,
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Nu t Gr o w e r ’s G uide
a late flowering variety is more appropriate than an early variety. Temperature data loggers can be installed on the orchard site for a few seasons to obtain accurate temperature data.
Rainfall While irrigation can provide crop moisture requirements, reliable rainfall is essential to replenish water storage. No irrigation system is as effective as soaking rain when it comes to replenishing soil moisture. Further, irrigation is expensive and costs are therefore reduced if rainfall is reliable. However, too much rain may cause problems with soil drainage, disease and fruit set. A rain-free period during summer and early autumn is important for minimising disease problems, particularly in almond and pistachio. A dry harvest period is also desirable for all nut crops to ensure nut quality.
Humidity One of the problems in high rainfall areas is the increase in disease due to high humidity. Humidity is generally higher in coastal regions than it is inland. High humidity increases incidence of bacterial and fungal diseases and some insect pests. Of course, tropical nuts such as cashew and macadamia are well adapted to a warm humid climate.
Wind While air movement is beneficial in reducing humidity and therefore disease problems, too much wind can be physically damaging to young trees causing limb and trunk breakage and stunted growth. Strong wind is very damaging to trees in full production
A weather station records accurate data in this hazelnut research plot (L. Snare).
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W h a t n u t g r o ws wh er e?
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and limbs that are laden with fruit are easily broken. In some instances, complete trees can blow over. Strong winds at flowering can reduce fruit set and constant wind can also cause disease problems when it prevents routine spraying for pest control. In areas of light sandy soil not protected by ground cover vegetation, wind erosion may cause soil to blow, leaving tree roots exposed. Constant wind also dries soil and can seriously affect water delivery via sprinkler irrigation. In windy locations, windbreaks should be planted before a nut orchard is established to provide shelter for young trees (see Chapter 5).
Soil The ideal orchard soil could be described as a soil that: • • • • • • •
provides no physical or chemical barrier to root growth has good drainage has adequate water-holding capacity contains adequate nutrients contains an adequate amount of organic material contains a healthy level of soil organisms is sufficiently stable to withstand erosion
Perhaps the most critical factor is soil drainage. Trees will not grow or produce good crops if the soil is heavy clay and becomes soggy when wet. Having said that, at the opposite end of the scale, free-draining light sands are not suitable either because they contain little organic matter and soil organisms, have little moisture and nutrient holding capacity and they are prone to erosion. The ideal soil in general, is a deep friable sandy loam that lies somewhere between light sand and heavy clay. One should not think that because land is sloping that drainage is good. Seldom is it, however, that one is able to find the perfect soil without soil modification measures to improve organic content, break up hard layers in the profile, or adjust soil pH. The pH of a soil is measured on a scale of 0–14 and this scale describes the level of acidity or alkalinity. Less than pH 7 is regarded as acidic and more than pH 7 is regarded as alkaline. A reasonably neutral pH enhances the availability of nutrients in the soil; if the soil is too acidic or alkaline, nutrient deficiencies can occur. Therefore, the ideal pH of a soil is about 7, however, while some crops are more tolerant of acidity or alkalinity than others, most crops grow well in a pH between 6 and 7.5. Soil acidity can be reduced by cultivating in lime before the orchard is planted and it is advisable to do this where the pH is less than 6. Reducing the pH to reduce alkalinity is more difficult to achieve. Salinity is an increasing problem in agricultural areas and the soil profile should be checked to ensure it is free from saline ground water. Nut trees generally do not tolerate saline conditions although pistachios show some degree of tolerance (see Water supply below). For optimum tree growth and nut yield, saline soils should be avoided. A detailed soil survey conducted by a surveyor with experience in nut production should always be carried out in order to ascertain soil suitability. This is particularly important when planning to grow a nut crop that is new to an area.
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Nu t Gr o w e r ’s G uide
Water supply While most nut trees will survive without irrigation, trees will not produce commercial quantities of nuts without adequate moisture, particularly during fruit development. Inadequate soil moisture during nut development can result in small nut size and poor kernel fill. Soil moisture requirements vary from nut to nut but while pistachios are better adapted to hot and dry conditions than nuts such as walnuts that hail from higher rainfall regions, both pistachios and walnuts require adequate soil moisture for commercial production. The amount of water needed for commercial nut crops therefore varies from nut to nut. Water requirements also vary according to the local climate, soil, and growing conditions. A figure of six megalitres (Ml) per hectare (ha) is often quoted as a guide for water requirements of high density orchards. However, in regions of high rainfall, organic-rich soil and mild summer temperatures, water requirements could be less than this, while in regions of sandy soils, high summer temperatures and low rainfall, over 14 Ml ha–1 may be required. Knowledge of the local climate and soil conditions and the requirements of the particular nut variety are therefore paramount before one is able to estimate the annual amount of water required for each hectare of nut trees. Water supply sources include regulated and unregulated rivers, dams and bores. However, diversion from rivers may be capped and no new permits issued. It is usual, therefore, that land is purchased with an existing irrigation licence and a permit to divert water is obtained. The reliability of the supply varies from river to river depending on the demand for the water, the size of the water storage upstream, and the reliability of the rainfall in the catchment. In some irrigation systems, additional water is available during dry seasons but at a greatly increased cost. It is a matter of deciding how much one can afford to pay for water. In other situations licensed pumping from unregulated streams is banned when river levels drop in dry seasons and this is the very time trees need it most. Some river water also becomes saline in dry seasons and may be unsuitable for horticultural use. Bore water is an option where there is a supply of underground water but the quality of the water varies and the supply can be unreliable when it is needed most. High quality irrigation water is particularly important for nut trees and regions supplied with saline water should be avoided. Although nut trees are generally intolerant of saline water, research in California has shown that pistachios grown on certain varieties of rootstock will tolerate water of up to 8 dSm–1 without significant reduction in tree growth and nut yield. Perhaps the most reliable supply of water for an orchard is a private off-stream dam that is designed with sufficient capacity for the specific irrigation requirements. In many regions a dam can be filled at little cost during times of peak river flow. In other situations there may be sufficient catchment on the property to store adequate supply for an orchard for one or two years. When calculating water requirements, it is wise to work on the worst case scenario to ensure the water supply is sufficient for the driest seasons.
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W h a t n u t g r o ws wh er e?
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Location Landform The more level an orchard site is, the easier it is to carry out all the mechanical operations required on a nut orchard. A reasonably level surface is particularly important for harvest machinery, although some harvest methods can be successful on sloping land. During orchard establishment and the production years, tractor movement is constant in the orchard. In some orchards, mowing and weed control work can be managed by small tractors or all-terrain vehicles but larger horsepower tractors are required for air-blast sprayers and harvest machinery. It can be dangerous to operate large machinery on sloping land and the operation is generally less efficient. Hilly land in areas of high rainfall may be subject to water run-off that can cause soil erosion and reduce the amount of moisture soaking into the soil. Similarly, where there is water run-off down a slope, irrigation is less efficient than it would be on level land. Aspect can be an important consideration where mountains are in close proximity to an orchard site because they may cause shading that reduces valuable sunlight hours. Valley areas are often prone to fog and poor air movement that can increase disease problems and valleys are also prone to frost that can reduce or eliminate nut set.
Previous land use It is important to check the previous land use because the soil may have been contaminated by chemical residues or soil diseases. Land that has been used for some cropping activities may have been subject to prolonged pesticide application, while land that has been used previously for orchard use may have root residue in the soil and the presence of the root-rotting fungus, Armillaria. Similarly, where existing bushland has to be cleared from an orchard site (assuming a clearing permit is available), Armillaria is likely to establish on the roots remaining in the soil and this may affect the orchard trees in the future.
Proximity to neighbours and wandering animals In most situations it is necessary to fence an orchard to protect the trees from wandering animals. While wandering stock should be the responsibility of the stock owner, there is no guarantee. Where the land is close to bushland, kangaroos, wallabies, possums, rabbits, wombats, pigs, goats and deer can be troublesome, especially to young trees. These animals are more difficult to fence out and if the wildlife pressure is great, nut production may be better sited elsewhere. In rabbit-prone areas, young trees may have to be protected with small guards. Where an orchard is near a residential area or close to neighbours, the use of chemical sprays and sound deterrents for bird protection may not be permitted, and if they are permitted, the problem with unhappy neighbours may cause ongoing social problems. Sulphur-crested cockatoos are widespread in Australia and while they may not visit when the orchard is young, they are sure to arrive when there is a good supply of nutty food. In some areas, crows and other parrots are troublesome in nut orchards and sound and visual deterrents are required to protect the crop.
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The benefits of growing nuts in a nut growing region Apart from proven environmental suitability, there is good reason to grow nuts in a nut growing region because there is likely to be expert technical support. Having other nut growers nearby provides an opportunity for sharing information and problem solving. Similarly, in nut producing regions contract machinery is more readily available and this can reduce the cost of production. If a grower is to be self-sufficient with all management operations, a large amount of machinery is required and this is generally not cost-effective unless the orchard is extensive. Having the option of contract machinery therefore improves the cost-effectiveness of small- to medium-scale producers. Nut processing facilities may also be available in high nut producing regions. In Australia, most almond growers in the Riverland and Sunraysia transport their harvested nut crop to one of the processors in the area. Likewise, in the Sunraysia area pistachio growers transport their crop to the facility at Robinvale, and in northern New South Wales and southern Queensland, many pecan growers sell their crop to ‘Stahmann Farms’ at Toowoomba where the nut processing facility is located. Macadamia growers in New South Wales and Queensland have the choice of several processors that can process macadamia nuts. Chestnut growers in the main chestnut growing area in north-east Victoria, can opt to send their nuts to larger growers who have established markets. Transporting nuts to market is also simplified in a popular horticultural area simply because there is a suitable transport network.
A nut orchard as a home and business When buying land for nut production, it is wise to consider whether it would be preferable to live on the orchard or live nearby. While it is idyllic to build your home amongst the nut trees, when the time comes to retire from nut production or move on for other reasons, you may be forced to move from your home. If, however, you purchase land for an orchard and a home nearby on a separate title, home life is less affected when it comes time to sell the orchard. Living off the farm also means that at the end of the working day, there can be more separation between work and home life.
Further reading Australian Nut Industry Council website http://www.nutindustry.org.au Horticulture Australia website http://www.horticulture.com.au/project Kenez, J. E. (1999). Dormancy, chilling and budbreak. Australian Nutgrower 13(3), 3. Knox, I. (Ed.) (1992). ‘Exotic Alternatives’. Agmedia. (Rural Industries Research and Development Corporation: East Melbourne.) website http://www.rirdc.gov.au/reports/index.htm Wilkinson, J. (1995). ‘Small Farming for Pleasure and Profit’. (Penguin Books: Australia.) Wilkinson, J. (1996). Getting started for small nut growers. Australian Nutgrower (10)1, 3. Wilkinson, J. (2003). The ideal soil. Australian Nutgrower 17(3), 3. Wymond, J. (1996). Getting started in the nut industry. Australian Nutgrower (10)1, 5.
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4 Propagation
While hazelnut trees are usually propagated by layering, all other nut trees grown for nut production are propagated by grafting or budding. Thus, a suitable variety is budded or grafted onto a suitable rootstock. Nut trees can also be propagated by cutting and micro-propagation. These propagation techniques are forms of vegetative propagation that ensure that the characteristics of the new tree will be the same as the tree from which the tissue was taken. This enables growers to select particular characteristics. Trees that have been grown from seed are variable and do not necessarily exhibit the characteristics of the parent. Seedling trees are therefore not suitable for commercial nut production.
Preparation of rootstocks and bud wood Rootstock varieties are generally selected for tree vigour, resistance to root disease and compatibility with the cultivar to be propagated, and in the case of grafted hazelnut trees, for lack of suckering. Wood of the chosen cultivar is selected for yield, nut quality, vigour, pollination characteristics, disease resistance and growth habit. The rootstock is very often a different species to that of the scion or bud wood. Some growers choose to plant rootstock seed in their orchard and later bud onto the growing rootstock seedling in situ. However, most growers purchase commercially budded or grafted trees from a reputable nursery or propagate their own trees. While planting nursery grown trees is more costly, the trees are usually at least one-year-old at planting and that saves a year or so of growing time. Also, tree growth is more uniform when an orchard is planted out with nursery-propagated trees than when trees are field-budded in situ. Nonetheless, rootstock seedlings grown from seed sown in situ develop a deep permanent root system. Generally, where rootstock seed is sown in the orchard, experienced propagators are contracted to do the field budding.
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Deciduous nut trees grown in a commercial nursery are generally grown and budded in nursery beds and offered for sale in the winter as bare-rooted stock. Evergreen trees such as macadamia are generally grown in pots in a sheltered environment, grafted or budded in the nursery and later offered for sale as potted trees. Bare-rooted deciduous trees are dug and are available for planting during winter dormancy, while potted evergreen nut trees are available most of the year. Trees grown for the collection of wood for use in propagation are known as mother trees. The exact identification of each mother tree is crucial to the correct identification of the propagated trees. The accuracy of identification throughout the nursery system is absolutely vital and it is one reason that growers should seek out reputable nurseries. The success of propagation is largely determined by the health of the mother trees and rootstock. Providing ideal growing conditions such as shelter from wind and optimum moisture and nutrition therefore is likely to produce the best success rate in propagation. Where the weather outdoors is too cool for vigorous growth, the nursery trees are best grown in a glasshouse or polyhouse, and where the sun is too hot the trees are best grown in a shade house. Before rootstock seed is sown it is cleaned of husk and stratified if necessary. While some seed such as macadamia seed, does not require stratification, seed of most deciduous trees is artificially stratified to replicate the natural cold climate cycle. This is done by placing the seed in a moist medium in a cool-room or refrigerator for about six weeks. The seed is then potted into potting mix or planted out into nursery beds. In frosty regions it may not be necessary to stratify seed artificially before sowing. Work to ensure the young seedlings are watered, fertilised, weeded and free from pests and diseases is crucial to the success of the propagation procedure. Rootstock seedlings are ready for budding or grafting when the trunk of the rootstock seedling is of an appropriate size: usually pencil to finger thickness.
Propagation techniques Budding Budding is done in the growing season and buds are taken from wood grown in the current season. There are different methods of budding but the most common methods used in nut tree propagation are patch budding, chip budding and T-budding. All involve placing a leaf bud onto the cambium layer that lies beneath the bark on the trunk of the rootstock seedling. Crucial to the success of budding is the vigour of both the mother tree from which the bud wood is taken and the rootstock seedling. Budding should not be attempted on rootstock seedlings that are not actively growing. Success is also determined by the quality of the bud, the speed of the operation, and the skill of the operator. Like grafting, budding relies on good contact of the rootstock and bud cambium cells. The time of budding varies between climatic zones and while budding may be more successful in tropical regions during spring or autumn, in temperate areas budding is usually carried out in summer when the night and day temperatures are most even and the growth is most vigorous. Good sap flow results in easy lifting of the bark and good
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callusing of the bud union. Bud wood is collected just prior to budding. Always look for plump leaf buds on newly ripened wood that is of a diameter approximately matching that of the rootstock trunk. Long neck buds are generally not used for budding. To avoid problems with large leaf petioles on bud wood (particularly on walnuts), the leaves on the bud wood to be used for budding should be trimmed back to the petiole a week prior to collection. When the bud wood is collected, the petiole will abscise creating leaf-free wood for budding and better seal of grafting tape. The bud wood is placed in a cool moist environment during transport. Budding is the preferred propagation technique where large numbers of trees are propagated because only one bud is required to produce each tree. To avoid drying, the bud is removed from the bud stick immediately before placing onto the rootstock. In hot climates, buds are usually budded onto the shady side of the rootstock trunk to reduce extremes of heat from the sun and produce a straight trunk as bud growth tends towards the light. In windy sites buds are budded onto the windward side of the trunk to reduce breakage of the fragile growing bud. Buds may start growing within a week or they may take a few weeks depending on variety and environment. The rootstock seedling can be headed back about a week after budding to stimulate growth of the bud. Side shoots growing on the rootstock may also be removed. After 21 days the bud should show signs of growth and the grafting tape should be removed. Sometimes buds may remain dormant for some months but generally there is growth within a few weeks. Buds that have not ‘taken’, look and feel dry and hard. If the season permits, a second bud can be tried. Patch budding. This technique is exact and more time-consuming than other budding techniques. Patch budding is used for species that are not so easy to propagate such as walnuts and pecans, because it gives a greater area of contact of the cambium cells. Large leaves are best removed prior to collection of the bud wood to ensure a better seal when taping (see above). Using a sharp propagation knife or a patch budding tool that has two parallel blades, a square patch of bark containing a plump bud is cut out of the bud stick. The patch is then carefully lifted and removed and a check is made to ensure the bud eye is present on the underneath surface of the bark. A matching patch of bark is then removed from the trunk of the rootstock seedling and the patch with the bud is quickly placed on the vacant patch of bark on the rootstock with the bud facing upwards. It is important that the bud is held firmly and taped into position. If necessary, a knife is used to trim the patch of bark to ensure a neat fit. If the bud patch is slightly smaller than the rootstock patch, firm contact of the cambium layers is assured. If the bud patch is slightly larger than the rootstock patch, the bud patch may bubble up and contact of the cambium would be reduced. The patch is taped firmly into position, leaving only the bud exposed. If the rootstock bark is rough, a grafting sealant may be needed along the edge of the tape to ensure a good seal. Chip budding. This is similar to patch budding but it can be done throughout the year and is a preferred method where the wood has thickish bark. Using a sharp knife, a cut is made down into the wood beneath the bark on the trunk of the rootstock (see diagram).
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Patch bud (left), T-bud (middle) and Chip bud (right).
A second cut is then made across the base of the chip so that the chip can be removed. A matching chip containing a bud is taken from the bud stick and placed firmly where the chip was taken from the rootstock. It is then taped into position and sealed. T-Budding. This method is common in almond propagation and other trees that are relatively easy to propagate. The leaves are removed from the bud stick and a short petiole can be left attached for ease of handling. A shield-shaped piece that contains a bud is cut from the bud stick; a T-shaped slit is cut into the bark of the rootstock; the bud piece is held by the petiole and it is slid down from the top of the T-shape behind the flaps of bark. The bud is held into position and sealed with grafting tape. T-budding may be done in summer using current seasons growth, in spring using bud wood collected during winter dormancy, or in autumn when the bud heals but does not grow until the following spring.
Grafting
A hot callusing tube is installed to assist grafting.
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Grafting wood that has more than one bud is known as scion wood. It is generally taken from dormant oneyear-old wood. In the case of spring or summer grafting of deciduous trees, pieces of scion wood are collected in winter, the ends are sealed with grafting wax and they are stored at 0–4°C °C C until required. Grafting may be done at various times but it is most often a winter operation. As warmth enhances the growth of cambium cells, hot callusing tubes are used for difficult to graft species such as
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walnuts. A hot callusing tube can be made of PVC piping with vertical slots that accommodate the trunks of the newly grafted rootstock. The tube can be heated via pumped air or a hot water pipe is installed down the tube to maintain a constant temperature. The hot callusing tube is secured along the row of growing rootstock seedlings and removed after callusing of the unions is apparent. Whip and tongue grafting. This method is used for young trees because the rootstock and scion wood must be of matching diameter. The rootstock is cut off diagonally, the base of the scion stick is cut off to a matching angle and a tongue or slit is cut vertically into the face of both diagonal cuts. The scion wood is positioned firmly on the rootstock so that the tongues ‘hook’ together and the cambium layers are in contact. The graft union is bound together firmly with grafting tape. Bark grafting. This method is generally used for top-working older trees (grafting established trees to a different variety) because the rootstock can be considerably larger in diameter than the scion wood. Bark grafting is therefore a common method used for changing a tree from one variety to another. The tree is first pruned back leaving a trunk one to two metres high, or large limbs can be cut back to stumps. On older trees, one or two low ‘nurse limbs’ are usually left attached to the trunk. Bark grafting of deciduous nut trees is generally done in spring or summer when the day/night temperatures are Whip and tongue graft. relatively similar. Two parallel slits are cut into the bark at the top of the trunk, the base of the dormant scion wood is cut off diagonally and inserted down behind the bark flap on trunk so that the diagonal cut is not visible. The bark flap and bud stick are held in position by one or two fine nails or staples and the cut face of the trunk is sealed with grafting paste. One or more grafts can be made in each trunk or branch. The newly grafted wood is best covered with newspaper or sisalation for protection from hot sun and cool night air. While top-working a tree causes loss of yield, the loss is temporary and the newly grafted tree will generally produce nuts in the second year.
Layering This method involves propagating stems while they remain part of the parent plant. Hazelnuts are the only nut tree propagated by layering. There are three main layering methods. Mound layering. This is the most common method used in hazelnut propagation. In spring when the new suckers have
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Bark grafting – scion wood and finished graft.
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Mound layering.
grown around the base of the mother tree, the weak suckers are removed and the strongest suckers are prepared to enhance root growth. One method is to girdle the stem of the sucker near the base by clamping it with a metal ring. Another method is to injure the bark and apply a root hormone compound. While girdling and hormone treatment are not essential, they increase layering success rate. The base of the growing suckers is then covered with a mound of friable soil or mulch-type material such as sawdust. The mound of mulch is kept moist and the mother plant is irrigated and fertilised to ensure optimum growth. Where conditions are favourable, roots grow from the base of the suckers into the mulch and each sucker may grow two metres in height. During winter dormancy, the mound of mulch is carefully removed and each sucker and its new root system is severed from the mother plant. The new trees are then ready for planting.
Tip layering. This technique produces new trees from older wood by layering suckers that are 2–3 years old. In spring when the suckers are in vigorous growth and the wood is flexible, the sucker is bent down until it is below ground level close to the base of the mother tree. The tip of the sucker is bent up at this point and notched at the bend, or the bark is scraped with a sharp knife and the injury is treated with rooting hormone compound. It is then secured to the soil with a strong peg and the tip of the sucker is tied to a stake to hold it in a vertical position. Friable soil or mulch is then mounded over the pegged down bend of the sucker and kept moist. During winter dormancy, the mulch is removed carefully and the rooted sucker is severed from the mother plant. Trees propagated from older wood should bear nuts sooner than trees propagated from suckers of one season’s growth. Trench layering. This technique produces many new trees from one sucker but new trees are small. In spring when a well-grown sucker is flexible, it is bent down to the ground and held in a horizontal position in a trench. The sucker can be notched, or bark scraped and treated with hormone compound to stimulate rooting. It is pegged down in the shallow trench and covered with friable soil or mulch such as sawdust. The mulch is kept moist and the mother tree is watered and fertilised to ensure optimal growth. Many new suckers may grow upwards from the buried sucker. In winter, the layered sucker is uncovered and cut into as many pieces as there are suckers, each with a separate root system. These new trees are small and may require growing on in a nursery bed for a year before planting out into the orchard.
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Cuttings Nut trees can be propagated by cutting with varying degrees of success where it is preferred that trees are grown on their own roots. Propagation by cuttings is sometimes used for rootstocks. Vigour of the mother plants is crucial to the success of this form of propagation. Wood suitable for cuttings is semiripened and is usually collected as one-year-old wood in summer or autumn. All leaves are removed and the wood is cut into lengths some 20–30 cm long. The base of each cutting is dipped in a root-promoting substance and inserted 60–100 mm deep into a propagating medium. Bottom heat is required to enhance callusing at the base of cuttings. The root system that develops from cutting-grown trees is more fibrous than the root system that develops when Semi-hardwood cuttings. a tree is propagated by seed.
Micro-propagation This method is performed in a laboratory situation using in vitro techniques. It is used to propagate rootstock, particularly hybrid rootstock, and own-rooted trees where very large numbers are required. Pieces of plant tissue, usually of tip growth, are taken from parent plants that have been grown under controlled conditions. These pieces are called explants. Explants are surface-sterilised before placing in a nutrient medium. The balance of nutrients and plant hormones in this medium determines the type of explant growth. During the first stage, the medium promotes shoot tip growth and then it is transferred to a multiplication medium where numbers increase rapidly. The explants are then divided, treated with a root promoting substance and planted in a propagation medium. The growing plants are gradually ‘hardened’ to a greenhouse environment and finally outside conditions.
Micro-propagation: Stem pieces are placed on a nutrient medium with gelling agent. Plant hormones in the medium stimulate axillary buds. Shoots are then divided into sections and re-cultured.
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Further reading Adem, H. (2002). Walnut trees grown in the field. Australian Nutgrower 16(3), 22. Alexander, D. Mc E., and Lewis, W. J. (1998). ‘Grafting and Budding Fruit and Nut Trees.’ (CSIRO Publishing: Melbourne, Victoria, Australia.) Allen, A. (1986). ‘Growing Nuts in Australia.’ (Night Owl Publishing: Shepparton, Victoria.) Australian Nut Industry Council Ltd website http://www.nutindustry.org.au Bennett, C. (2000). Quality nursery trees. Australian Nutgrower 14(2), 18. Bennett, C. (2003). High quality propagation material. Australian Nutgrower 17(4), 35 Dann, I. (1995). Field budding walnuts. Australian Nutgrower 9(3), 18. Dela Cruz, F., and Fletcher, R. (2002). Superior cashew trees. Australian Nutgrower 16(1), 10. Furneaux, R. (2000). Propagation for hazelnuts and walnuts. Australian Nutgrower 14(2), 21. Gathercole, F. (1996). Where to with rootstocks? Australian Nutgrower 10(4), 23. Kenez, J. E. (2001). Hazelnut propagators meeting. Australian Nutgrower 15(2), 27. Lewis, H. (2002). Walnut trees on their own roots. Australian Nutgrower 16(3), 24. Messina, J. (2002). Pistachio propagation. Australian Nutgrower 16(3), 25. Nesbitt, M. (2003). Grafting demystified. Australian Nutgrower 17(3), 29. O’Kane, B. (1999). Growing chestnut varieties for the consumer. Australian Nutgrower 13(4), 15. O’Kane, B. (2001). Top-working chestnut trees. Australian Nutgrower 15(2), 24. Stephenson, R., and Gallagher E. (2001). Selecting better macadamia varieties. Australian Nutgrower 15(1), 14. Wilkinson, J. (2001). Top-working walnut trees. Australian Nutgrower 15(2), 26. Wilkinson, J. (2002). Gray Plantations Nursery. Australian Nutgrower 16(3), 20. Wilkinson, J. (2002). Growing hazelnuts the Megalong way. Australian Nutgrower 16(4), 20. Wilkinson, J. (2003). Growing trees at Powell’s rootstocks. Australian Nutgrower, 17(2), 25.
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5 Planting a nut orchard
It has often been said that you plant nut trees for your grandchildren. This is an old myth and probably refers to seedling trees that can take more than 15 years to produce nuts. Modern cultivars usually produce a few nuts in the first or second year after planting and produce a harvestable crop by year six. This sounds exciting but before planting any trees there is work to do in preparing the soil, laying out the tree lines, installing irrigation, and establishing windbreaks.
Soil preparation Correcting soil problems before planting is relatively easy to do. Correction after planting may be impossible. Where the soil is deep and well-drained, of neutral pH and rich in organic matter, little soil preparation will be required and work before planting may be as simple as cultivation of the tree lines and weed control. However, where drainage is not adequate, soil is shallow or low in organic matter, considerable soil modification is necessary to ensure good tree growth and long-term production. The results of a detailed soil analysis and site survey will determine what orchard preparation work is required before planting. When surveying the site, contour levels and soil types are identified and different soil types are separated into different orchard blocks. This allows management operations such as irrigation and fertilising to be tailored to suit each particular block. Soil analyses by an independent soil laboratory should be undertaken to determine soil depth, whether deep-ripping is necessary and whether drainage is adequate or if soil modification to improve drainage is required. Soil analysis also determines whether the pH is high or low and what amount of organic matter and nutrients should be added to ensure optimum tree health. An analysis of the biological activity in the soil is available through the Soil Foodweb Institute (website http://www.soilfoodweb.com).
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The orchard site should be cleared of rocks and other obstacles that may cause problems with orchard machinery. If the site was once an old orchard or had large trees growing on it, the soil should be cultivated and all buried roots removed because these roots can become host to honey fungus (Armillaria spp.) that can cause root-rot in nut trees. Earth moving machinery may be required to level hollows and mounds and improve drainage. Sloping sites on heavy soil may require contour drains while low-lying sites may require underground drainage pipes to remove excess moisture. Another strategy to improve drainage is to add gypsum to the soil. Gypsum (calcium sulphate) causes fine particles (such as clay particles) to flocculate forming larger aggregates and larger pores in the soil. This facilitates better drainage. Good drainage is particularly important where rainfall is high during tree dormancy. Where soil depth is less than desirable or a hard pan underlies the topsoil, deep ripping can be undertaken to improve the soil structure. Ripping to a depth of at least one metre breaks up hard layers in the tree lines and has been shown to improve drainage and root penetration. Another soil modification technique is to increase the depth of topsoil using a road grader to move the soil from the inter-row onto the tree line. While mounding the treeline increases depth of topsoil, it may not suit mowing or harvest machinery designed to operate most efficiently on a level surface. Where the pH of the soil is below 6, i.e. the soil is acidic, lime should be spread on the site and cultivated into the soil. In acidic soils, high aluminium content can become toxic to plants and restrict the availability of important nutrients. In general, more lime is needed to raise the pH in clay soils than in sandy soils. While liquid lime products are available, the most cost-effective method of reducing soil acidity is to spread ground limestone. A high organic content is most desirable in orchard soils. Soil organic matter refers to the living and dead plant and animal material in the soil. Organic carbon is a measure of the organic matter in soil. Organic matter improves drainage in heavy soils, increases the water holding capacity in sandy soils and enhances the activity of soil organisms. Soil organisms also improve the fertility of the soil and create pores, maintaining a good soil structure. Soil organic matter can be increased by growing cover crops such as annual rye grasses, cereal and legume crops in the tree lines before trees are planted. Cover crops are generally sown over the whole orchard site in the spring prior to planting and then cultivated in before they set seed some months later. Covering the tree rows with straw and manure and allowing this to decompose before incorporating it all into the soil with a cultivator is an excellent method of increasing the organic content before planting. Many growers mulch around individual trees with lucerne hay or mulch the complete tree line by rolling out round bales of straw. This enhances tree growth and is an excellent way to reduce the weed growth around the tree, improve soil organic content and reduce loss of soil moisture. It is always wise to check beforehand that the mulch is not contaminated with troublesome weeds. Cultivation of the orchard site also assists with weed control. Repeated cultivation may be required where self-seeding weeds are a problem. However, some weeds may persist and require spraying with a systemic herbicide. It is always wise to eradicate troublesome weeds prior to tree planting.
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Orchard layout and tree density Layout of an orchard will vary according to the topography, the soil type, the type of nut tree to be planted and the intended management. Tree lines are usually set in a north — south orientation to optimise sunlight. Where the terrain is hilly, rows may be placed on the contour to optimise moisture penetration and reduce erosion. Whatever the intended tree density, ensuring sufficient space for mechanical activity between rows and at the end of rows is essential. Where the tree lines are not straight, row curving should be slight and tight corners should be avoided. Because nut trees take some years to produce crop volume, some growers plant their orchard at double density with the intention of removing alternate trees at a later date when trees mature. Another strategy to make use of orchard space in the early years and generate an early cash flow is to inter-plant nut trees with faster growing fruit trees or a fodder crop. Of course this introduces new management demands and care must be taken to ensure the growth of the young nut trees is not compromised by the presence of the short-term crops. In general, the best plan for a nut orchard is to plant the trees at the optimum spacing for that variety and site, and maintain ground cover growth so that the turf can be mown to add organic matter to the soil. In high density orchards the usual layout is parallel rows of trees with the inter-row or traffic lanes one or two metres wider than the spacing of the trees in the tree lines. Tree spacing in a high density orchard ranges from four to ten metres apart depending on the type of nut tree (see specific nut chapters for spacing details). High density orchards can be hedged when the canopies mature to maintain sufficient light penetration. Large growing trees such as chestnuts and pecans can be planted on the square or at wide spacings to ensure sufficient light penetration in the long-term. One advantage of planting on the square particularly for organic production, is that the orchard can be mown in both directions, largely eliminating the use of herbicides for weed control. When the orchard layout is set and the tree lines have been marked out, windbreaks can be planted and irrigation installed.
Windbreaks In windy sites plantations of tall vegetation will reduce wind and enhance tree growth. Space for windbreak plantations should be allocated in the orchard layout, be it around the perimeter or as subdivisional windbreak plantings. Windbreaks are best established well prior to planting of the nut trees to ensure immediate protection for the growing nut trees. The fastest growing plants for windbreak strips between tree rows in a young orchard are tall vigorous grasses such as Jumbo sorghum or maize in temperate regions and Bana grass in tropical areas. These grasses can be removed when the trees are mature. Where a permanent windbreak is required, the windbreak trees should not be too tall or they will rob the adjacent orchard of sunlight and moisture and falling leaves and sticks will obstruct harvest machinery. Dense shrubs that suit the local area are the most appropriate species for a permanent windbreak but they should be chosen carefully because some species may attract nut-eating birds or rats. Planting shrubby indigenous
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Plantings of Giant Sorghum are grown between every four rows of almond trees to provide wind protection for young trees.
species is likely to be the best solution and these species may also attract beneficial birds and insects.
Irrigation systems Designing an irrigation system to suit a particular orchard is extremely complex and best done by an engineer who specialises in orchard irrigation. Irrigation technology is constantly changing as new products are manufactured and electronic technology is improved. Factors to consider in the design include the terrain, the size of the orchard, tree density, long-term water requirements of the trees, water availability and cost, water quality, type of emitter and pumping distances. Factors to consider in choice of emitter include the soil type, type of nut tree, tree age, susceptibility to disease and water availability. The simplest design would be a level site where the water source is half way along the orchard row and the main supply dissects the laterals radiating out along the tree lines. However, seldom is an irrigation system so simple. Where water is to be pumped over long distances or the orchard is sited in hilly country, maintaining constant water pressure from one end of a line to the other requires special equipment. The cost of irrigation can greatly affect the cost of nut production and it varies according to water prices and pumping costs. Where electricity is installed at the pump site, pumping at night optimises the cheaper power rate. Where electricity is not installed at the pump site, diesel engines are required. Water pumped from the water source into a main pipe must be filtered to prevent blockages. Large capacity water filters are fitted to remove small and large particles that could block sprinklers and drippers and create mineral deposits in the line. Where water quality is not reliable, more than one filter may be required.
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In orchards divided into multiple blocks, the main supply line may branch into smaller diameter sub-mains and then into lateral lines that deliver the water along the tree lines. While it is costly in the initial stage, installing supply lines that have the capacity to irrigate for the life of the orchard is cost-effective in the long-term. Installing lines that are only sufficient to do the job when the trees are young usually proves to be false economy. In general, all main and sub main irrigation lines are laid underground and lateral lines down the tree rows are laid on the ground surface. There are numerous types of emitters and irrigation technology is constantly changing. In general, high density orchards are supplied with mini- or micro-sprinklers or drippers, while low density orchards of larger widely spaced trees may require larger capacity impact sprinklers to achieve sufficient coverage of the root zone. Where the supply and line capacity permits, sprinklers and drippers can be upgraded so that they deliver more water as the trees grow. The selection of drip or sprinkler systems is site specific. Drip emitters or pressure compensated drip tubes are fitted with pressure compensating devices to ensure equal distribution of water along the length of the irrigation line. Drip systems are preferred where: water supply is limited; water quality is less than desirable; low humidity is required to minimise fungal and bacterial diseases in the canopy; wind affects the spray pattern of sprinklers, and trees are young and root systems cover a small area. Orchard drip systems usually begin as one poly-line when trees are young and this is upgraded to two poly-pipe laterals as the root zone widens. The lines are laid along each tree line on the ground surface and where two lines are installed, one is positioned each side of the tree line.
Single line drip irrigation is adequate when walnut trees are very young.
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Mini- and micro-sprinklers irrigate a wider area of the root zone than drippers. They are preferred where: the root zone is wide and a large area is irrigated; the soil is sandy and soil moisture spread is limited; water supply is plentiful. Sprinkler heads range in capacity and coverage. Mini- and micro-sprinkler systems are usually supplied with a single line down the centre of the tree line. The capacity of this line is usually greater than it is for laterals supplying a drip system. The area wetted by the sprinkler can be upgraded as trees grow by changing the nozzle size or installing more sprinklers. Evaporation losses from sprinkler systems are considerably higher than they are in drip systems. Irrigation lines that cross traffic lanes must be laid underground, and where possible lateral lines along the tree lines are positioned so they are least obstructive to mowing and harvest machinery (see Chapter 5 for more detail). An option in mature orchards to keep lateral lines out of the way of machinery is to suspend the line from an above-ground wire that spans the length of the tree line and is supported at each tree. Constant maintenance is needed, particularly with sprinkler systems, to keep emitters free from weeds. This is usually done by spraying with herbicide. Weed growth in a young orchard is particularly vigorous because there is little shade from tree canopies. While weed growth around drippers is not as obstructive to the water delivery as it is with sprinklers, controlling the growth reduces moisture loss and blockages. It is important that emitters are positioned a distance from the tree to ensure water does not run down the trunk or pond around the base of the tree because this can cause root-rot disease. Sprinklers are usually positioned in the tree line half-way between the
Mini-sprinklers have been installed halfway between trees in this pistachio orchard.
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trees, or on either side of the tree some distance from the trunk. Sprinkler irrigation produces a spray mist that may rise into the tree canopy and increase humidity. Even where water does not splash onto the foliage, the increase in humidity may increase disease incidence. This can be particularly troublesome in almonds and pistachios. Drippers are installed at an appropriate distance either side of the young tree and if the lateral lines are designed to allow for increased flow, additional drippers can be installed as the trees grow. Placement of drippers should ensure soil is moist out to the edge of the canopy (drip-line). In mature orchards, each tree may require as many as 12 or more drippers evenly distributed around the root zone. In a young orchard where tree canopies are not shady, the delivery lines can become extremely hot in the sun and it may be necessary to schedule irrigation during the night or early morning. In low density orchards where the trees are large and widely spaced such as in some walnut, chestnut and pecan orchards, larger impact or pop-up sprinklers can be installed in the inter-row so that the entire orchard floor is irrigated. Other irrigation systems include underground ‘leaky hose’ systems but blockages are difficult to detect and even more difficult to fix. Portable irrigation lines may be suitable in some situations but flood irrigation is not recommended due to the large quantity of water required. For best tree health, growth, and nut production, adequate moisture should be maintained in a large root area of the tree. But how does one know how much water to apply to prevent soil drying or becoming too wet? While digging a hole in the orchard or taking soil core samples can provide a good indication of the moisture in orchard soils, this is time-consuming and likely to disturb the root system. There are many methods of determining when to irrigate and how much water to apply. The most commonly used method is based on soil moisture using monitoring devices. In large orchards, irrigation systems are very often computer operated; the irrigation scheduling is controlled by data collected by moisture sensors installed throughout the orchard. This data can be downloaded via a modem back to a central office where the irrigation schedule can be adjusted. However, in smaller orchards, manual soil moisture monitoring devices are installed at various points throughout the orchard. These points should represent the full range of soil types and tree maturity. The devices are inserted into the soil so that the reading is taken at different depths, e.g. 30 cm, 50 cm and 80 cm. The devices are read manually and the irrigation applied accordingly. It will be observed in time how the weather affects irrigation scheduling. In most regions, summer heat and wind has a dramatic drying effect on soil moisture and substantial rainfall is required to negate the need for irrigation. The simplest soil moisture monitoring device is a tensiometer tube that consists of an airtight water-filled tube with a porous ceramic tip that is buried in the ground. As the soil dries, water is drawn out of the tube through the ceramic tip and a partial vacuum develops within the tube. This is registered on a vacuum gauge. As the soil wets up after irrigation, the vacuum within the tube draws water back into the tube and the reading on the gauge falls. The tubes can be constructed from PVC pipe, with a ceramic tip and rubber stopper and read via a portable vacuum gauge fitted with a hypodermic needle. Alternatively, commercial tensiometer devices known as Irrometers™ (Irrometer Co. Inc., California, USA) have a vacuum gauge fitted to the head of the tube.
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Higher-tech soil moisture monitoring devices operate by various methods. Gypsum blocks measure soil water tension by the electrical resistance between two electrodes embedded in gypsum. Devices known as ‘neutron probes’ contain a radioactive source that emits neutrons. The neutrons collide with hydrogen atoms in the soil and the rate of collision is measured in counts usually over a set time period. There is a direct relationship between the number of hydrogen atoms and the soil water content. Other devices measure soil moisture via electrical capacitance sensors. These devices use a high frequency electrical field created around each sensor that extends through the plastic access tube into the soil to provide an accurate soil moisture measurement. The fact that the sensor is not in contact with the soil ensures the sensor is not affected by its surrounding environment. Another high-tech device is called a ‘Time Domain Reflectometry’ (TDR) probe. This technique relies on transmitting a pulse of energy into the soil. Most of the energy of the pulse propagates out into the soil, but a small portion will be reflected back. The speed at which the energy travels is influenced by the moisture content of the soil. Another method of determining when and how much water to apply is based upon plant water use. This is determined from meteorological data and depends on how long it takes for the calculated water use to deplete the reserves of water in the soil. The aim is to apply sufficient irrigation water to replace the water used by the tree since the previous irrigation. This is calculated from free demand for water and pan evaporation (Epan) where an exposed water surface is positioned in the orchard and its evaporation measured. Another method is evapotranspiration (ET). Here the plant water use is calculated from weather data such as wind speed, humidity, temperature and solar radiation.
Planting trees When the soil has been prepared, weeds have been removed and irrigation systems are installed, trees can be planted. Deciduous trees are usually planted as bare-rooted trees during winter while evergreen trees are purchased as potted trees and can be planted at any season but spring is usually the favoured time. Where there is risk of crown gall, it is wise to prevent infection of trees before planting by dipping the tree root system into a solution of anti-gall inoculant. There are also organic pre-planting dips that may protect trees from root-rot and this treatment may be worthwhile in areas prone to root-rot infection. When planting bare-rooted trees it is essential that the roots are kept moist at all times. When the trees arrive at the orchard they are ‘heeled’ into moist soil or sawdust, and during transport to the planting site the roots are covered with a moist material such as hessian. Most growers pre-dig the planting holes mechanically to speed the planting operation. Hand digging follows to ensure the planting hole is large enough to accommodate the roots without root bending. Long roots should be trimmed to fit and any damaged roots should also be trimmed off. Trees grown in containers should be cut out of the container to minimise disturbance to the root ball, and any bent or misshapen roots are pruned off. If the soil in the bottom of the hole is loose it should be compacted down to prevent the tree sinking after planting. The tree is held in the planting hole and soil is crumbled
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Bare-rooted trees are ‘heeled’ in to prevent root drying before planting. Here almond trees are heeled in at Century Orchard.
around the roots. The tree is firmed in so that it is planted at the same height that it was in the pot or nursery bed. The graft union should always be above the soil line. The trees are watered immediately after planting and in most regions it is necessary to stake the trees to protect them from wind damage. Stakes are secured in the ground beside the trunk and they need to be strong and of a material that will be durable until the tree no longer requires staking. Hardwood and cane stakes are commonly used but steel rod or piping is more durable and can be re-used. Trees are generally tied to the stakes using a soft but strong material or tape in a figure-of-eight tie. This ensures the trunk will not be damaged. There are conflicting ideas about pruning at planting. Where bare-rooted trees have been root-pruned before planting, it is wise to reduce the canopy size to balance this root reduction. Pruning of the leader is also recommended at planting to stimulate new growth. When delivered from the nursery, trees generally form a single whip shape and it is usual to head this back to a plump healthy bud. Some growers head back very hard reducing the leader by more than half while other growers may head back to the topmost good bud. Trees that are to be trained to a vase-shape may have lateral branches at planting and these can be selected at this time. In some instances, trees can be left until the following year before tree training commences. The need for tree training at planting depends upon the particular type of nut tree and also on the quality and shape of the trees delivered. Where rabbits are a problem or weedicide protection is required, the trunk of each tree can be fitted with a plastic or cardboard sleeve. Some types of nut trees in some regions also require protection from sunburn. White acrylic paint or shade sleeves are two options available for sunburn protection. (See the specific nut chapters for more details on planting.)
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Further reading Adem, H. (1995). Design of an irrigation system. Australian Nutgrower 9(3), 7. Adem, H. (2001). Cover crops to increase organic matter. Australian Nutgrower 15(2), 6. Adem, H. (2002). Early bearing and high yields. In ‘Proceedings of the Australian Nut Industry Council Conference’. pp. 71–73. (Australian Macadamia Society: Lismore, NSW.) Adem, H. (2002). Fertigation. Australian Nutgrower 16(3), 5. Agriculture Victoria, State Chemistry Laboratory, Werribee (1998). Soil and plant testing for horticultural crops. Australian Nutgrower 12(3), 10. Australian Nut Industry Council Ltd website http://www.nutindustry.org.au Black, J. D. F. (2003). Young trees under trickle irrigation. Australian Nutgrower 17(4), 19. Horticulture Australia website http://www.horticulture.com.au/project Kenez, J. E. (1999). Dormancy, chilling and budbreak. Australian Nutgrower 13(3), 3. Monson, T. (2004). Be bee-friendly during pollination. Australian Nutgrower 18(2), 6. NSW Agriculture (2003). Orchard Plant Protection Guide: Weed Management. Australian Nutgrower 17(3), 4. Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Van den Ende, B. (1999). Tree pruning and training. Australian Nutgrower 13(2), 3. Wilkinson, J. (2002). Soil moisture measuring techniques. Australian Nutgrower 16(4), 6.
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6 Managing a nut orchard
When the trees are planted and the irrigation system is up and running the real challenge begins.
Management of young trees The main aim with young trees is to achieve maximum tree growth and reduce the time to the first harvest. To do this the trees need optimum growing conditions and lots of tender loving care. To think that newly planted trees can be left to their own devices apart from ocassional weekend irrigation is nonsense. Success in nut production lies with good orchard management in the early years. It must be remembered that the root system of a young tree is limited and to support the growing canopy soil moisture and fertility must be adequate at all times. A young tree is sensitive to fluctuations in environmental conditions, to competition from weeds, and stress from wind and pests. If growth ceases during the growing season it may not re-start until the following season. To maintain adequate soil moisture the frequency of irrigation in a young orchard may be as often as every day or two during very hot weather, but water demand varies according to the age of the tree, the type of nut tree, rainfall, soil type, temperature and wind strength. In trial orchards, it has been shown that frequent applications of low doses of fertiliser throughout the growing season promote excellent growth of young trees. Frequency of application may be more often than once per week. It has been shown that frequent applications of nitrogen and potassium during the growing season will produce excellent growth in young trees. Of course promoting ideal growing conditions for young trees also creates ideal growing conditions for weeds. Weed control, however, is difficult around young trees because the trunk is green and the tree is susceptible to herbicide damage. Non-systemic or ‘knock-down’ herbicides are safest to use around young trees because the risk of
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permanent tree damage by herbicide contact is minimal. Using equipment fitted with spray drift protectors offers good protection, but, even so, it is unwise to use a systemic herbicide close to young trees at any time of year. It is also unwise to spray in windy weather. Orchard ground cover growth such as weeds, cover crops and pasture, is particularly vigorous in a young orchard because there is full sunshine and the moisture demand of the young trees is confined to a small area. Ground cover growth can be controlled with herbicides, however, mowing is preferred in a young orchard because of the susceptibility of young trees to herbicide damage, and also the mown turf increases the organic matter in the orchard. It is tempting to allow sheep or other livestock to graze and reduce the need for mowing the expanse of vegetation in a young orchard, but there is little doubt that the damage the animals cause to irrigation fittings and to trees exceeds any benefit. (See Management of the orchard floor below.)
Irrigation Irrigation is the number one task in both young and mature orchards because adequate soil moisture is essential for tree growth, nut yield and nut quality. As outlined in Chapter 4, the water requirements of a nut orchard vary with the type of nut tree, age of tree and the local climate and soil type. In fact the range of annual water requirements for high density orchards can extend from 4 Ml ha–1 to 14 Ml ha–1. Walnuts are often considered the most thirsty nut tree and pistachios the least thirsty nut tree. While all nut trees will survive without irrigation when grown on good horticultural land, irrigation is essential for production of a commercially viable nut crop. However, exceptions do occur. Macadamia trees in the high rainfall zone of coastal Queensland and northern New South Wales produce good crops without irrigation in good seasons, and chestnut trees in some growing regions produce well without irrigation in good seasons. However, even in favourable conditions, young macadamia and chestnut trees are like all young nut trees and grow best when irrigated in dry weather. Design of an irrigation system is best handled by an irrigation engineer. Factors to consider in the design include site levels of the orchard blocks and the length of the delivery lines, the pressures and volumes required for adequate distribution of water to all trees, the capacity required for the pumping system, and the capacity of the irrigation lines and emitters. Once this data is established and the irrigation system is designed, the first pipe can be laid. Generally, nut orchards are irrigated via under-tree sprinklers or drippers and the soil moisture in the root zone is monitored by soil moisture measuring devices. These devices range from simple tensiometer tubes to sophisticated computer-controlled devices that can be downloaded via modem back at the main office. (See Chapter 4 for an outline of irrigation systems and soil moisture monitors.) The root zone area of a mature nut tree can extend into the inter-row and the greater the area of root zone irrigated the greater the uptake of moisture will be. For best water distribution, therefore, emitters should be positioned so that the complete root zone, or
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Almond irrigation using drippers and daily pulsing. Note extensive root system, six metres wide, with feeder roots dispensed over entire area (C. Bennett).
Almond irrigation using drippers and irrigation every 2–3 days (without pulsing). Note concentration of feeder roots close to drip line (C. Bennett).
as much of the root zone as possible, is irrigated. This is easier to achieve with sprinkler systems because the distribution area is larger and sprinkler capacity can be upgraded to match the root zone area as the trees grow. Wetting the entire root zone is not so easy to
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achieve where drip systems are installed, especially in sandy soils where there is little outward movement of moisture in the wetted area around each dripper. Increasing the number of drippers will increase the wetted area. The frequency of irrigation can also be managed to maximise the outward movement of moisture around drippers. It has been found that ‘pulsing’ increases the width of wetted area and this is achieved by repeated short irrigations e.g. one hour on, one hour off, one hour on. The number of drippers installed around each tree is only limited by the capacity of the irrigation system and in a mature orchard the number may exceed 12 drippers per tree. Drip lines are best installed 50 mm beneath the soil surface, because where aboveground drippers are installed in two lateral lines, one either side of the tree line, mowing under the canopy is not possible. If mowing is desired, the irrigation lines must be moved to the centre of the tree line or removed completely. They may also need to be moved or removed before harvest to make way for sweepers and pick-up machines. Sprinkler systems that are positioned along the centre of the tree line can usually be avoided by mowers and harvest machinery. Laying all piping underground reduces problems with harvest and mowing equipment. One way of installing irrigation lines off the ground away from animals, mowers and harvest machinery is to secure the delivery line to a wire that is suspended along the tree line one metre or so above the ground. Both sprinklers and drip emitters can be fitted to the suspended line. The wire must be sufficiently secure to take the weight of a line full of water. In orchards of large trees such as mature walnut, chestnut and pecan orchards, growers may install pop-up or impact sprinklers in the inter-row to water a wide area of the orchard floor. Piping is laid underground to allow tractor access down the inter-row and in some cases the sprinklers can be disconnected and removed for mowing and harvest operations. Irrigation of the inter-row, especially when the orchard is young, may be used to grow a fodder crop that can be harvested to provide early cash flow. Use of soil moisture monitoring devices provides an insight into the moisture uptake of a tree. Experience may show that the depth of moisture required in the soil profile of a particular nut orchard may be less than one would expect for deep rooted trees. Very often it is found that the tree takes up moisture from the top half metre of soil only, and that soil moisture readings below a depth of 60 cm do not change significantly from one irrigation to the next. Installing soil moisture measuring devices at different depths in the soil profile from 30 to 80 cm, will show how deep the irrigation water should penetrate to effectively re-charge the moisture in the root zone. If soil moisture measuring devices are not installed, too much irrigation water may be applied that may leach nutrients from the root zone and cause root disease, or too little irrigation water may be applied and the root zone may remain dry. Severe fluctuations in soil moisture are detrimental to tree growth and nut yield and quality. Soil moisture readings should be accessed daily during the growing season to determine the required frequency of irrigation because daily weather fluctuations greatly affect plant water use. Growers soon learn the particular weather conditions that cause an increase in water demand. High temperatures, low humidity and wind are the three main factors increasing water demand. On the other hand, high humidity, low temperatures, cloud cover and calm weather will reduce water demand. While rainfall replenishes soil
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moisture, during the growing season a significant amount of soaking rain is required to circumvent irrigation. It is recommended that growers ensure adequate soil moisture down to a minimum depth of 80 cm at the start of the growing season because it is difficult to moisten soil at this depth during the growing season when the tree’s demand for moisture is high. Frequency and duration of irrigation scheduling therefore will depend on the tree requirements and the local climate. Of course in an orchard where there are differing soil types and tree ages, some sections of the orchard will require different irrigation schedules to other sections. Poor irrigation management can result in disease problems. Too much water can result in root and trunk rot that in severe cases may result in death of the tree. Irrigation systems should, therefore, be positioned so that water does not drain down the trunk or pond near the base of the tree. Sprinkler systems operate via spraying water droplets and in doing so the humidity in the tree canopy is increased. This increase in humidity and water splash on the tree foliage can increase disease problems, particularly in nut crops that are prone to fungal and bacterial diseases. Drip systems do not significantly increase the humidity in the canopy, so they are preferred in crops such as almond and pistachio. Whatever irrigation system is installed, weeds thrive in the moist growing conditions. Weeds growing around sprinklers are particularly troublesome because they obstruct the water distribution pattern. Weed control around dripper systems is less critical and control work is required less frequently than with sprinkler systems. Nonetheless, all excess growth under the tree canopy will rob the tree of moisture and should therefore be kept short, particularly during the growing season. Herbicides are the only practical way of controlling weeds around fixed irrigation equipment because most equipment is plastic and easily damaged. Mowing, mulching and slashing weeds either side of the tree line is possible where emitters and piping are installed along the centre of the tree line. (See Orchard floor management below for more detail.) Peak water demand in a mature nut orchard occurs during kernel development and oil accumulation but adequate soil moisture is also essential during bud initiation and flowering. The exact timing of these stages varies from one type of nut to another and from one variety to another. (See irrigation information in specific nut chapters.) Irrigation is reduced or ceased prior to harvest to avoid deterioration of nuts that fall to the ground and to reduce damage to the orchard floor by harvest machinery. Maintenance of irrigation equipment is required prior to the commencement of irrigation each season. This may involve unblocking and/or replacing emitters, upgrading the capacity of emitters or delivery lines, checking the water distribution of emitters, and servicing moisture monitoring equipment, pumps and filters. Lines may require flushing during the season to prevent blockages. Water is perhaps the most valuable commodity in horticulture and efficient water use is essential to minimise cost and wastage. Growers should try to ensure that the water storage or the allocated amount of water available for the season will extend at least until after harvest. Ideally, the amount of water available should more than cover the highest usage likely for the season. Where the stored or allocated quantity is not adequate, water saving measures should be put in place from the beginning of the season. Irrigation
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specialists can assist in advising growers on techniques to reduce water consumption without significantly jeopardising tree health, the developing crop and future crops. These techniques may include installing drippers instead of sprinklers, ‘pulsing’ dripper delivery by doing repeated short irrigations, regular weed control, increasing the organic content in the soil, and reducing wind in the orchard. (See Chapter 5.)
Tree nutrition and fertilisers The major elements essential to plant growth are nitrogen (N), phosphorus (P) and potassium (K) (or potash) and these make up the bulk of fertiliser requirements in a nut orchard. Three elements that are required in small amounts are calcium (Ca), magnesium (Mg) and sulphur (S). Trace elements that are required in very small amounts are iron (Fe), manganese (Mn), zinc (Zn), boron (B) and copper (Cu). The most commonly applied fertilisers in horticulture are high in nitrogen and potassium. Phosphorus and mixed fertilisers containing the full range of minor elements are generally applied on an annual basis. Specific trace elements are applied when they are known to be deficient. Different types of nut trees have different nutrient requirements but it is generally accepted that all nut trees have high nitrogen and potassium requirements during both the early growth years and the production years. Of course, fertiliser application will be less for trees growing in fertile organic-rich soil than it will be for trees growing in sandy soil low in organic content. Nutrient demand in mature orchards is also dependent upon the size of the crop harvested. Estimating the quantities of nutrients removed from an
Symptoms of potassium deficiency in hazelnut leaves (L. Snare).
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orchard when the crop is harvested is important in determining the nutrient requirement for that orchard. Less nutrients are removed when the hulls are left under the trees or spread back in the orchard after harvest. To avoid a decline in productivity and tree health the nutrients removed must be replenished. It has been estimated that the nutrients removed per tonne of crop harvested could approximate 8 kg nitrogen, 6 kg potassium, 2 kg calcium, 1 kg magnesium as well as trace element removal including manganese, iron, boron, zinc and copper. Nutrients are also removed from the system when trees are pruned and the prunings are removed from the orchard. The demand for different nutrients, particularly in bearing trees, varies according to the stage of tree growth and the stage of nut development. When a nutrient is deficient, there may be obvious visible signs such as leaf yellowing in the case of nitrogen deficiency, but leaf yellowing can also be caused by disease or inadequate moisture. The most accurate method of assessing the nutrient status of a mature tree is annual analysis of leaf tissue and this is done in conjunction with soil analyses. Leaf analysis involves collecting leaves and sending them to a laboratory for testing. Instructions for collecting the samples are given by the particular laboratory, but in general, a number of fully expanded leaves from each tree variety and from each orchard Table 2 Nutrient content of common fertilisers Fertiliser
Nitrogen %
Phosphorus %
Pottassium %
Sulphur %
Calcium %
Magnesium %
Straight inorganic fertilisers Urea
46
Sulphate of ammonia
20
DAP
19
Single superphosphate
24 20
3
8.8
11.0
Muriate of potash
20.0
50
Sulphate of potash
41.0
16.5
Lime
35–40
Dolomite
12–22
8–12
Gypsum
14–18
19–22
Organic fertilisers Pelleted poultry manure
3.0–3.6
1.6–3.6
1.0–1.6
Broiler litter poultry manure
1.4–1.5
0.6–2.4
0.6–1.9
Source of data: O’Hare et al. (2004). ‘Macadamia Grower’s Handbook.’ (Department of Primary Industries and Fisheries: Queensland.)
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block are collected in mid-summer. These leaf samples are labelled because results will vary according to tree age and variety and soil type. Leaf analysis is costly and there’s no point in collecting a mixed bag of leaves and expecting accurate results. By dividing the orchard into blocks of similar requirements, fertilising demands can be organised accordingly. (A table giving the desired nutrient levels is given in the fertiliser notes in each chapter on specific nuts.) By checking the results of the leaf analysis against the normal nutrient level for a given nut tree, the nutrient requirements of the trees sampled can be calculated. Analysis laboratories can supply this information and horticultural scientists can recommend a fertiliser regime. It is important that records be kept of all leaf analyses so that a history of an orchard block can be established. It is also important that the leaf samples are taken at the exact time of year every year as the stage of growth and time of year can greatly affect leaf nutrient levels. A complete soil analysis is usually conducted prior to soil preparation at planting to ascertain presence of hard layers, soil pH and salinity status as well as fertility and presence of disease. However, it is useful to conduct regular soil tests during the life of the orchard and the results should be used in combination with the leaf analyses when determining a fertiliser regime. The reason for this is that while soil nutrient analysis gives a general picture of soil fertility, it does not always reflect tree nutrient status. In addition, it is not uncommon for an element to be present in the soil but for various reasons, that element may not be available to plants. This could be due to unfavourable soil pH as discussed under ‘Soil preparation’ in Chapter 4. To have greatest benefit, small amounts of fertiliser are applied regularly through the growing season. This reduces leaching and provides the tree with a continuous supply of nutrients. The type of fertiliser applied can be adjusted to suit the stage of nut development or tree growth. For instance, during the growing season between early spring and autumn, fertilisers for deciduous nut trees may include a broad spectrum fertiliser, potash-rich and calcium-rich fertilisers and high nitrogen fertilisers. Some applications may be ground spread while others may be delivered through the irrigation system (fertigation). Factors that determine the actual formulation of a chosen fertiliser include its acidifying effect on the soil, the desired method of application, and whether a slow release fertiliser or highly soluble fertiliser is appropriate. Cost is also an important factor. Acidification caused by repeated application of certain fertilisers can be a problem in orchard soils particularly where the soil pH is lower than desirable. Nitrogen is available in many formulations and the acidifying effect of the different formulations varies. The solubility of the formulations varies also. For instance, while urea is an inexpensive nitrogen fertiliser to apply, the application of lime may be required to counter its acidifying effect. On the other hand, calcium nitrate is an expensive and highly soluble form of nitrogen fertiliser to apply but it does not have a significant acidifying effect on the soil. Some forms of nitrogen fertiliser are lime-coated to counter an acidifying tendency. The traditional method of applying granular fertilisers in a nut orchard is via a tractor-mounted spreader along the tree row. Both pelleted and granulated products are highly suited for ground spreading. However, most nut growers use a combination of
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methods to supply trees with nutrients. Fertigation is an increasingly popular method during rapid growth and nut development because delivery is quick and easy. Fertigation is the application of soluble fertilisers via the irrigation system. These fertilisers are dissolved in water and the solution is fed or injected into the irrigation system at the required rate. Fertigation is usually done toward the end of an irrigation event to avoid leaching of the nutrients. Spraying the foliage with a dilute solution of liquid fertiliser is also an option but foliar fertilising is time-consuming and expensive. It is therefore generally only used for applying trace elements such as zinc where a deficiency is identified, or where an unfavourable soil pH prevents the uptake of an element via ground application. The uptake of elements via foliar application is relatively rapid. Another option in maintaining tree nutrition is to apply organic fertilisers such as manures and composts. Organic growers work to feed the soil that in turn feeds the trees. Soil chemistry is very complex and a balance of the different elements is important to soil health as is the role played by soil organisms. Providing a favourable organic-rich environment for soil organisms is therefore most desirable. The organic content of soil is also important for maximising the water-holding capacity of soil, for improving drainage, and for its role in acting as a buffer in soil chemistry. For these reasons, growers strive to increase the organic content of orchard soil by the addition of mulch or by mowing the ground vegetation onto the tree line. Of course, mulching is seldom practical when trees are in production because decomposition may not be complete at harvest and the mulch can obstruct harvest machinery. While organic manures do not contain a high nutrient profile, the nutrients are available to plants over a period of time and they provide organic matter. Growers using only organic fertilisers generally include other soil fertility measures such as growing cover crops and applying soil enhancers (see Chapter 6). Whatever ground fertiliser is used, nutrients are not available to plants unless there is adequate soil moisture.
Canopy management Training the tree canopy includes pruning and hedging as well as using limb-bending techniques. Tree training is a controversial topic of discussion between growers because there are as many training methods as there are varieties of trees. Basically the aim is to develop a strong branch framework and maintain optimum light penetration in the canopy. A strong framework is established when trees are young. When growth slows as trees come into bearing, the focus of tree training turns to maximising fruiting wood and maintaining a desirable size and shape to suit the orchard spacing and harvest method. There are a few technical points that help to explain the reasons behind tree training: • Individual shoots gain vigour when the number of buds is reduced. • There are many dormant growth buds at the base of a branch that are stimulated when the branch is cut back. • Fruiting requires sunlight and to retain productivity throughout the canopy, sunlight must penetrate the canopy.
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Poor tree training during the early years has resulted in weak crotches in this walnut tree.
• Pruning consists of two main types of cuts: heading cuts where a branch is shortened, and thinning cuts where the whole branch is removed. • A pruning wound heals most rapidly if a branch is cut back to a very short stub rather than if cut flush at the join. • A wide angled branch is a strong productive branch; a neck bud produces a narrow angled branch that has a weak crotch. This latter type of branch will almost certainly break during the life of the tree in high wind or when loaded with crop. • Horizontal branches are more fruitful than branches that are vertically inclined. • Tree shaping is most effective when trees are in good health. In fact, tree training goes hand in hand with irrigation and tree nutrition management.
Training young trees Tree training begins in the first growing season when the intended tree shape is established. Natural tree shape is a varietal characteristic: each variety of nut tree will grow naturally to a particular shape. For instance, one variety of pecan may tend to grow pyramidal in shape and lend well to a central leader shape while another pecan variety may grow into a more weeping shape and tends naturally to have multiple leaders. While tree shape can be manipulated, it is always easier to work with the natural tree shape than try and produce a shape that is unnatural for that variety. Some nut trees will require little tree training while other nut trees will require continual training for the first 4–5 years. At planting, young trees generally form a single whip shape and it is usual to head this back to a plump healthy bud because this will stimulate vigorous growth. Once in strong growth, the secondary branches that form can be trained to encourage the desired tree shape. Pyramidal-shaped trees form a central leader with lateral branches radiating
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evenly out from that leader. Training trees to an open-centre or wine glass shape involves selecting about four main limbs that radiate out from the trunk. Where trees are planted at close spacings or are intended to form a hedgerow, the canopy is initially shaped to form a strong framework that will suit mechanical hedging. This may be a central leader or a modified open-centre. When the desired leader or leaders are selected, all other competing branches are removed by rubbing out buds that are forming in the wrong place, or by heading back young branches that are too crowded or compete with the leader. Neck buds produce weak branches and should be removed. Young branches that are growing at an acute angle should also be removed because these branches have a weak crotch and may eventually break in windy weather or when loaded with crop. Low branches below one metre on the trunk should be headed back or removed because these will hinder tractor access as the tree grows and obstruct tree shaking. Broken and crowded branches should also be removed. The ultimate shape desired of the tree should be kept in mind at all times (see specific nut chapters for more detail). While pruning of deciduous trees was traditionally done during winter dormancy, pruning of all young trees is done throughout the growing season to remove problems before they develop. Further shaping can be done in winter if required. Pruning is always done in dry weather to minimise the risk of disease. Once tree shape is established, the goal in training a young tree is to maximise tree growth and stimulate fruiting wood to produce a harvestable crop as soon as possible. One technique to stimulate fruiting wood is limb bending. This involves bending the lateral branches down to a horizontal angle while they are young and flexible. By continually bending the branches down, the growth tends to become more horizontal and more fruitful. This technique is used where producing a crop is more desirable than branch growth. When growth of a young tree is halted and no new growth develops despite favourable growing conditions, hard pruning may stimulate latent buds into growth. Where the branch formation is stunted and misshapen, it may be best to prune the young trunk off below the branch junction and develop a new trunk. The new leader should be tied securely to a stake until the growing point has strengthened. Wind can be damaging to young trees, particularly when the trees develop a large canopy before the trunk is of sufficient diameter to support that canopy. Stakes are secured in the ground beside the trunk at planting and the trunk is tied firmly with a soft but strong tie. The ties should be checked regularly to ensure they are not too tight, too loose or broken. Where wind is troublesome, windbreaks should be established prior to planting. Where wind damage is likely it may also be necessary to prune the canopy back to reduce the weight and volume of foliage. While tree training takes time, training young trees is most important. A badly formed young tree will never become a strong productive tree.
Canopy management in bearing trees The main aim in training mature trees is to maintain light penetration in the canopy to maximise nut yield and nut quality. While a dense canopy is an asset for maximum photosynthesis when trees are young, as trees grow and the canopy extends for many
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metres, the centre becomes dark and unproductive. Therefore, branches must be thinned or the canopy must be hedged to improve light penetration. In hedgerow orchards, mechanical hedgers cut back all branches to a certain distance from the tree centre. In popular horticultural regions this can be done by hedging contractors. Usually only one side of a tree row is hedged in a season to avoid substantial yield reduction. In some nut crops alternate sides are hedged every second season, but the frequency depends on the fruiting habit and vigour of the nut tree. Because nuts fall to the ground when mature, tree height is not an issue for ease of harvest, but it is an issue when orchards are intensely planted and the height of one row of trees shades the neighbouring row. In this situation the canopy tops are reduced to maintain adequate light throughout the orchard. Where an orchard is extremely crowded and shaded, removing every alternate row of trees may be a more permanent solution in reducing shading in the long term. In most mature nut orchards, the loaded branches tend to bow down under the weight of the developing fruit and this can prevent mechanical access along the orchard inter-row. A necessary task with mature trees is, therefore, to ‘skirt’ the canopy by removing low branches. Broken and diseased branches are also removed. Pruning is usually done immediately after harvest to minimise crop loss and it is always done in dry weather to reduce the risk of disease. Branches and leafy debris discarded during pruning is generally carted away from the orchard for disposal elsewhere. However, where the amount of debris is not large, mulching machines can be used to chop up the prunings in situ. This practice leaves the material in the orchard system and adds organic matter but the mulch should have decomposed by the next harvest to avoid mechanical problems. Most nut trees will produce commercial crops for at least two decades if tree health is maintained. However, there comes a time when tree age results in declining vigour and smaller nut size. To maintain an acceptable level of nut yield and quality, a replanting program may be required. Tree replacement is usually done in stages to ensure a continual level of productivity. Replanting is very often beneficial in the long-term too because the new varieties that have become available since the original planting, may be more productive at an earlier age and the nuts may have more marketable qualities.
Orchard floor management In a young orchard ground cover growth is particularly vigorous due to the open situation but as the orchard trees grow and cast shade, ground cover growth slows. When trees are young, the inter-row can be sown to pasture or fodder crop and harvested or kept mown. Maintaining a cover of vegetation in the inter-row is desirable in both young and mature orchards because it provides habitat for beneficial organisms, reduces dust in the orchard, provides valuable organic matter when it is mown, and erosion from wind and water is minimised. Another benefit is that the pores created in the soil by the grass roots improve moisture penetration and reduce compaction. As mentioned in the Chapter 4, it is usual to sow the orchard area down to some sort of pasture mix such as rye grass and clover prior to planting. Clover is a legume and is
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Ground cover vegetation is allowed to grow longer during the dormant season in this almond orchard.
valued for its nitrogen-fixing properties. However, pasture species tend to decline without irrigation in dry seasons and more drought tolerant weed species gradually take over. In mature orchards, maintaining a good cover of ground vegetation can be difficult where there is dense shading from the tree canopies and where irrigation emitters distribute water only along the tree lines. Lack of moisture for ground covers is seldom a problem in areas of high rainfall. Machinery traffic, particularly from harvest equipment, also reduces the cover of ground vegetation. The species of ground cover sown, therefore, should be chosen for its suitability to the particular location and drought tolerant species are best sown where the inter-row is dry. Orchards of evergreen trees are permanently shaded, while deciduous orchards allow light penetration to the orchard floor during the dormant season. Shade-tolerant species of ground cover are therefore particularly necessary in macadamia and cashew orchards. The ideal management of the orchard floor when trees are young involves maintaining a completely weed-free tree line to enhance tree growth and ensure irrigation fittings are kept clear. As mowing close to the trees is not usually a proposition due to the potential damage to trees and irrigation equipment, growth of weeds and all other ground covers along the tree lines is usually controlled by herbicides. All ground cover growth between the sprayed tree-line strips is best mown. As the trees mature, some growers increase the width of the sprayed strips along the tree-lines to match the growing root zone of the trees. Other growers prefer to keep the sprayed strip along the tree lines to a minimum and continue to mow between the sprayed tree line strips. In deciduous orchards ground cover growth is usually allowed to grow higher in the dormant season because, this can reduce soil wetness and improve vehicle access
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particularly in high rainfall areas. It also increases habitat for biodiversity in the orchard and improves soil structure. There is a trend towards maintaining a completely bare orchard floor to reduce moisture loss to weeds. While broad use of herbicides saves time and simplifies management, it is not desirable because complete lack of ground cover vegetation exposes the bare soil to wind and water erosion, the soil surface may cake and become impermeable, and biodiversity and organic matter is lacking. In the past some growers cultivated the inter-row to reduce ground cover growth but this can damage tree roots. Where ground vegetation is sprayed with herbicides, some perennial weed species persist and are extremely difficult to eradicate. For this reason it is wise to alternate the type of herbicide used. Herbicides are divided into groups that have a particular mode of action and each herbicide belongs to a particular group. This information is provided on the herbicide label. The recommended routine is to alternate the herbicide group used so that the mode of action varies. It is sensible when spraying any herbicide around trees to minimise spray drift by using a sprayer fitted with a spray dome or shield that covers the spray head. Herbicides can be divided into two types, systemic and non-systemic. Systemic herbicides contain a chemical that penetrates the vascular system of the plant that is sprayed, killing the whole plant down to the roots. Non-systemic, contact or ‘knockdown’ herbicides ‘kill’ only that vegetation that is contacted and after an initial ‘knockdown’, most perennial weeds will re-grow. Non-systemic herbicides are safer herbicides to use around young trees where the bark on the trunk is thin and foliage growth is low. Safety to the operator is also important. Both non-systemic and systemic herbicides are toxic to humans and some are extremely toxic and should be used with great care according to directions on the label. Systemic herbicides can be further divided into specific herbicides and non-specific herbicides. Specific herbicides that are systemic are formulated to kill or target certain types of weeds and they include products for broad leaf weeds, products for woody weeds and products for grasses. Non-specific herbicides that are systemic are formulated to kill all they contact and they include the most commonly used herbicide in orchards, glyphosate. While this product may result in a complete kill, it is most important that one product is not over-used because over-use can lead to chemical resistance and poor weed kill. Regular mowing of ground cover vegetation is time-consuming but it is the most environmentally friendly management for the orchard floor. While the prime reason for mowing the ground vegetation in an orchard is to reduce the amount of moisture loss, mowing also prevents weeds seeding, adds organic matter and maximises air flow in the orchard. A mown orchard looks great too and the pride and satisfaction one gains from creating a beautiful work place should not be underestimated. Frequent mowing is particularly important prior to harvest to produce a clean orchard floor and minimise the organic litter on the orchard floor that could interfere with harvest machinery. Grazing animals are sometimes combined with nut production with the idea of keeping growth down, utilising the orchard area fully and providing an early cash flow. While this may be tempting, livestock and orchard trees usually prove to be a
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troublesome mix because no matter how much pasture is available for grazing, livestock like to add nut tree foliage to their diet. This results in permanent damage to branches and poorly shaped trees. Another big problem with livestock in the orchard is damage to irrigation equipment and the time and expense required replacing emitters usually puts an end to the grazing idea. Tree guards offer some protection but to be high enough, the guards may restrict or deform tree growth. Electric fencing can be installed either side of the tree line to protect trees and irrigation equipment but this seldom guarantees protection. Finally, while manure from livestock improves soil fertility, the animals must be removed at least two months before harvest to prevent contamination of fallen nuts.
Controlling orchard pests Management to reduce the incidence of pests and diseases Pests and diseases are more prevalent when a plant is grown in large numbers such as in a commercial orchard. In recent years Integrated Pest Management (IPM) has improved management of pest problems and reduced the use of pesticides. IPM is based on understanding the factors that make an orchard vulnerable to pests and learning how to prevent an infestation, or, failing that, learning how to control the infestation before it is widespread. This involves identifying the conditions favourable to the pest, monitoring the pest in the field, and using effective methods for prevention and control. Factors that affect the chance of a pest infestation include the weather, the location of the orchard, soil moisture and the health of the tree. The variety of a tree also has an impact because susceptibility to disease is a varietal characteristic. Some varieties are therefore better suited to some regions than other varieties. The aim in reducing the incidence of pests and diseases in an orchard is to create an unfriendly pest environment. Many pests and diseases are more prevalent in a humid environment, therefore it is wise not to establish an orchard near the coast or in a low-lying valley where mist and fog are common. Growing almonds or pistachios on a coastal cliff top for instance is sure to bring on-going disease problems and a lifetime of frustration. It is also wise not to plant trees too densely because this decreases air circulation. As an orchard grows, pruning and tree thinning will assist in maintaining air circulation. Infestations of some insect pests, such as mites, are more prevalent in a dusty environment and this usually occurs on rows of trees adjacent to a dusty roadway or traffic lane. Naturally occurring beneficial insects can keep pest insects in check where there is ideal habitat for the beneficials. Planting windbreaks of local bush species and growing favourable ground covers in the orchard are two ways of increasing predator habitat. Very often, it is possible to use a biological control agent by introducing a particular beneficial insect that feeds on the pest. When introducing biological control agents, use of pesticides harmful to the biological control agent must cease. Infestations of insects and diseases can become devastating in a very short time, so orchard monitoring must be frequent to prevent an outbreak before it is widespread. Spraying of chemicals is an important tool in IPM. (See individual nut notes for control of specific pests and diseases.)
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Birds The most difficult pests to control in nut orchards are birds. From the time of kernel development in summer, nut-eating birds can visit the trees and reduce the crop to a carpet of dropped nuts and leaves. Birds arrive as soon as the kernel forms, well before nut maturity so the duration of bird control can be long and tiring. Some birds can also damage new buds reducing growth and nut set. Bird netting is seldom practical for nut orchards due to the vast area to be covered. Several species of birds are particular pests and arrive in great numbers and the same flocks of birds may return each year. Most pest birds are Australian birds that are protected wildlife, although permits to reduce numbers are available in some instances. Pest birds include ravens (commonly known as ‘crows’), sulphur-crested cockatoos, ganggang cockatoos, corellas and parrots. All nut crops except macadamia and cashew are prime food for these birds. Macadamias are protected from bird attack due to their hard shells and cashew fruit contain a toxic substance. Nut varieties that have a thin or soft shell are easier bird fodder than hard-shelled varieties but almonds, chestnuts, hazelnuts, pecans, pistachios and walnuts are all troubled by birds. Generally the softer the shell, the greater is the devastation and the greater the range of troublesome bird species. Methods of bird control include noise and visual deterrents and taste deterrents. Usually growers install one type of deterrent and this is backed up with occasional use of other deterrents. Noise deterrents include shot gunfire, riflefire, gun-fired ‘Bird Frite’ cartridges, gas-operated scare gun, permanently installed electronic scaring devices, radio alarms and model aircraft. Electronic bird scarers and gas-guns can be fitted with time clocks that can be set to operate between certain hours of the day. However, near residential areas, the noise can become a contentious issue and automatic noise deterrents may be prohibited or may not be worth the trouble from disgruntled neighbours. Where
Gas guns can be used in bird control.
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the orchard is remote from neighbours, automatic noise deterrents are most effective but they must be combined with shot gun and other deterrents. Most electronic bird scarers operate at regular intervals whether there are birds in the vicinity or not. However, certain systems (more expensive systems) can be fitted with radar equipment and operation is triggered when the device detects birds are present. Some electronic bird scarers operate via speakers mounted on high poles around the perimeter of the orchard. Much research has been conducted on the type of noise that is most scary to the different bird species. Noises used in bird deterrent equipment range from bird distress calls to gunfire and jarring screeching sounds. While most equipment is designed to deter a range of bird species, some deterrents can be made to deter specific bird species. I Recorded scare noises can be effective in bird control. have heard of growers recording their own scare noises and raucous music to play through the orchard and this may be loads of fun but its effectiveness in deterring birds is not guaranteed. Visual deterrents include reflective helium-filled balloons, reflective kites, flying hawks suspended on overhead lines and reflective windmills. Some growers have found these to be effective, particularly when used in combination with noise deterrents. Most of the pest bird species are cunning and quickly learn the distance of gunfire or become accustomed to the noise and visual deterrents. It is therefore essential to alter the pattern, change the type of ammunition and position of noise emission, and move the visual deterrents. Aeroplanes are also used to herd flocks of birds away from large nut orchards. Taste deterrents have not been commonly used as part of bird control management but they could be worthwhile. A bitter-tasting substance is sprayed onto the canopy as the first flock of birds arrive. While spraying the whole orchard would be an expensive exercise, there are usually a few trees favoured by the birds that could be sprayed or the perimeter row could be sprayed. On tasting the bitterness on the fruit, the birds become quite agitated and panic and leave the orchard. They seldom return for a second dose and follow-up sprays are usually not needed. Taste deterring products are non-toxic and are registered for use on food crops. Providing an alternate source of feed can assist in bird control also. More often than not when birds are sent away from an orchard, they fly over to the neighbouring orchard and remain in these trees until they are shunted back by angry gun fire of the neighbour. However, if the orchard is the only source of feed around, it is helpful to establish a decoy feeding site of grain away from the orchard and close to the bird’s favourite roosting
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place. Birds usually learn to associate farmers and their vehicles with the scare tactics and sometimes parking the vehicle in the orchard will be a deterrent for a short time, but like the scarecrow, the effect is not long lasting. The key with bird control is to learn the behaviour of the troublesome birds, get to know their movement patterns and their roosting places and be ready to strike as soon as the first birds arrive in the orchard.
Animals Tree-eating animals such as wallabies, kangaroos, possums and deer, as well as wandering livestock can cause havoc to young growing trees and appropriate fencing is essential. Rabbits too can damage young tree trunks. Some nut orchards, particularly those with dense canopies such as macadamia, harbour rats and these rodents can be devastating from a crop loss point of view and also from a health aspect. However, rodent numbers can be controlled or eliminated by removing undergrowth to reduce nesting places, and by installing traps and bait stations.
Chemical spraying to control pests and diseases in the canopy Tree diseases fall into three main categories: fungal, bacterial and viral. Mites and insect pests can also be controlled by chemical sprays. Diseases may be prevented or kept to an acceptable level by spraying the orchard trees with a protective chemical at susceptible times. Other diseases and most pests are sprayed with an appropriate chemical when field monitoring determines that there is a need to spray. The different chemicals used to control the different diseases are registered for use on specific crops. Complying with the recommendations of the label is essential to avoid contamination of a crop and prevent unacceptable levels of chemical residue in nut product. Certain nut trees are more prone to pests and diseases than others. Fortunately in Australia, we do not have the number of pest and disease problems that growers overseas have to contend with. It is crucial therefore, that imported plant material and orchard machinery is free from contamination and that strict quarantine regulations are adhered to. Most pests and diseases affect the foliage and developing fruit in the canopy of the tree and these are controlled via chemical applied to the canopy by air blast sprayer. These sprayers blast a fine mist into the tree canopy to cover all foliage with chemical. Good coverage of the canopy will depend upon the horsepower and capacity of the machine, the type of nozzles used and the speed of travel down the orchard row. While achieving full coverage of the canopy in an orchard of small trees is easier than achieving full coverage of large trees, all trees can be effectively sprayed given the right sprayer equipment. The equipment required for spraying large trees is high-powered and fitted with towers or special nozzles designed for tall canopies. Achieving good control of pests and diseases therefore begins with purchasing the most appropriate equipment for the orchard. To achieve an effective tree cover and efficient use of chemical, it is necessary to calibrate the spray equipment accurately and mix the correct concentration of chemical according to directions on the label. Of course chemical spraying is only one facet of controlling pests and diseases in an orchard. Spraying should be done in conjunction with other orchard management
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practices to optimise tree health. Reducing pest and disease problems may also involve changing the type of irrigation emitter to reduce humidity or wet foliage, or changing pruning techniques to improve air circulation. In popular horticultural regions, it may be possible to engage pest managers and spray contractors.
Pests and diseases in the tree roots and crown Unfortunately pests and diseases that affect the crown and roots of trees are very difficult to control. Improving drainage may reduce incidence of root-rot and various control methods have been tried to save trees from root and crown rot caused by species of Phytophthora but there is no quick fix. Cutting out rot-affected sections of the trunk and crown, and painting the wound with a paste made from a copper-based fungicide has been shown to be effective against some crown and trunk rot diseases. Applying a deep mulch of poultry manure and lucerne hay around the root zone of walnut trees affected by Phytophthora root-rot has improved tree health. Control of Phytophthora root-rot in some types of nut trees is controlled by applying a foliar spray of phosphorous acid (PA). Phosphorous acid has also been used as a trunk injection to control Phytophthora rootrot in chestnuts. All chemicals should be applied according to the directions on the chemical container. Armillaria, or ‘honey fungus’, is a root disease that can occur in orchards that are planted on land that was recently cleared. The fungus inhabits the rotting roots in the soil and moves onto the roots of nut trees. There is no effective control. Other soil-borne pests that are very difficult or impossible to control once established include root knot nematode and crown gall. Root knot nematodes, also known as eelworms, are microscopic. Crown gall is a bacterium. Both pests are soil-borne and soil tests should be conducted to ensure a site is free from infection before establishing an orchard. Root knot nematodes and crown gall cause lumpy growths on roots and both pests can be introduced into an orchard via infected plant material. Where there is risk of infection of planting stock, trees should be dipped before planting in appropriate treatment solution to protect them from infection. In some cases, treatment can be applied through the irrigation system.
Preparing the orchard floor for harvest Nuts fall from the tree when they mature. In most cases, the nuts are picked up from the orchard floor by pick-up machines that include vacuum harvesters, fingerwheel harvesters and rotary pick-up machines. All pick-up machines require a clean orchard floor to operate efficiently. Pistachio nuts are harvested by shake and catch machines that shake the trees and collect the nuts in a catching frame above the ground. In some chestnut orchards and orchards where trees are young or trees are few in number, nuts are shaken onto a ground sheet or picked up by hand. Whatever method is used, all harvesting operations are easier and most efficient when the orchard floor is clean and free of obstacles. The first task in preparing the orchard floor for harvest is to remove any hazards such as rocks and branches that may be lying under the trees, or holes made through wombat,
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rabbit, or fox activity. Holes and depressions can be dangerous for machinery operation, and because the sweeper and pick-up machine heads are some metres wide, nuts that roll into the depressions are not collected by the machine. Irrigation equipment positioned under the trees may need to be moved away from the path of machinery or removed completely. As mentioned under orchard floor management above, where there is ground vegetation, mowing is done regularly prior to harvest to ensure the turf is fine and decomposes quickly. Generally, irrigation is halted before harvest to ensure the orchard floor is firm and dry. This reduces soil damage by machinery traffic and also enhances nut drying, slowing the deterioration of fallen nuts. While nuts fall to the ground when they mature, nut fall can take many weeks and the small quantity of nuts that fall each day makes for inefficient pick-up. Therefore, in almond, pecan, pistachio and walnut orchards the trees are shaken with a tree shaker when the majority of nuts are ready to fall. Unfortunately, cashew, chestnut, hazelnut and macadamia trees are not shaken because shaking would bring down immature nuts. Tree shaking has many advantages. It allows growers to manipulate when the nuts fall, it concentrates harvest into a short period, nut quality is optimised because the nuts are not exposed to the weather while hanging in the canopy, and pick-up is most efficient. Where a tree shaker is used to shake the nuts to the ground, brittle wood in the canopy may fall down with the nuts, especially in older orchards, and it is usually necessary to do a stick pick up before a sweeper or pick-up machine is used. (See specific nut chapters for harvest details.)
Further reading Aarons, S. R. (2001). Soil biology. Australian Nutgrower 15(2), 7. Australian Nut Industry Council Ltd website http://www.nutindustry.org.au Bennett, C. (2003). Irrigation efficiency. Australian Nutgrower 17(3), 16. Bird Gard Australia (2000). Electronic bird control. In ‘Proceedings of the 2000 Australian Nut Industry Council Conference’. p. 12. (Place?:South Australia.) Black, J. D. F. (2003). Young trees under trickle irrigation. Australian Nutgrower 17(4), 19. Brown, P. (2004). Plant nutrition – an outline. Australian Nutgrower 18(4), 3. Byrnes, C. (1995). Chemical registration for nut trees. Australian Nutgrower 9(1), 12. Charlesworth, P. (2000). Monitoring soil moisture. Australian Nutgrower 14(4), 10. Crop Health Services, Victoria (1996). Sampling of specimens for analysis. Australian Nutgrower 10(4), 26. Dorahy, D. (2003). Fingerwheel harvesters. Australian Nutgrower 17(1), 10. Drew, H. (2002). The meaning of IPM. In ‘Proceedings of the 2002 Australian Nut Industry Council Conference’. p. 34. (Australian Macadamia Society: Lismore, NSW.) Drew, H. (2004). Critical issues in spray application in macadamias using ground-based air-assisted sprayers. Australian Nutgrower 18(3), 3–9. Falivene, S. (2004). Producers discover mix for fertigation success. Australian Nutgrower 18(4), 11. Firth, D. J. (2003). Organic matter and soil flora and fauna. Australian Nutgrower 17(3), 12.
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Guest, D. (1998). Effective management of Phytophthora. In ‘Proceedings of the 1998 Australian Nut Industry Council Conference’. (Ed. J. Wilkinson). pp. 33–35. (Australian Nut Industry Council Ltd:Bairnsdale, Victoria.) Hall, J. (2002). Chemical use approval. In ‘Proceedings of the 2002 Australian Nut Industry Council Conference’. p. 26. (Australian Macadamia Society: Lismore, NSW.) Hill, P. (1997). Effective tree pruning. In ‘Proceedings of the Australian Nut Industry Council Conference’. pp. 8–18. (Mildura, Victoria.) Hocking, G. (1996). Drip irrigation maintenance. Australian Nutgrower 10(4), 8. Horticulture Australia website http://www.horticulture.com.au/project Hudgson, B. W. (1999). Fertilisers for fertigation. Australian Nutgrower 13(4), 6. Malcolm, P. (2004). Leaf mineral concentrations in stone fruit are affected by root temperatures and phenology. Australian Nutgrower 18(4), 9. McMichael, P. (1995). Off-label and minor use chemicals. Australian Nutgrower 9(2), 7. McMichael, P. (1996). Chemical resistance. Australian Nutgrower 10(2), 25. Mitchell, P. D., and Goodwin, I. (1996). ‘Micro-irrigation of vines and fruit trees’. Agmedia. (Rural Industries Research and Development Corporation: East Melbourne, Victoria.) O’Connor, J. (1999). Fertigation methods and equipment. Australian Nutgrower 13(4), 3. O’Hare, P., Stephenson, R., Quinlan, K., and Vock, N. (2004). ‘Macadamia Grower’s Handbook.’ (Queensland Department of Primary Industries and Fisheries: Brisbane, Queensland.) Pudney, S., Proffitt T., Brown A., and Willoughby D. (2002). Soil moisture sensors. Australian Nutgrower 16(4): 12–17. Queensland Department of Primary Industries (1998). Efficient pesticide use. Australian Nutgrower 12(2), 3. Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Savage, J. (2002). Crows and cockatoos. Australian Nutgrower 16(4), 30. Slack, J., and Dirou, J. (2002). Nutrient removal in nut crops. Australian Nutgrower 16(3), 32. Temby, I. (1996). Nuts are for the birds. In ‘Proceedings of the 1996 Australian Nut Industry Council Conference’. pp. 12–18. (Albury, Victoria.) Van den Ende, B. (2000). Sunlight and orchard canopies. In ‘Proceedings of the 2000 Australian Nut Industry Council Conference’. pp. 31–36. (South Australia.)
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7 Organic nut production
What is organic agriculture? A commonly accepted definition of organic agriculture is ‘farming without the addition of artificial chemicals’ but organic agriculture is far more than this. The intention of organic farming is to encourage natural biological systems to maintain soil fertility and prevent pest and disease attack, while excluding the use of synthetic fertilisers and pesticides. An artificial chemical is a chemical that has been chemically processed, for example, natural rock phosphate is an acceptable addition on organic farms but superphosphate is not because the rock phosphate in this product has been processed with sulphuric acid to make it more soluble. The challenge in doing away with artificial chemicals is finding alternate management techniques and natural materials that work successfully in a particular orchard. While not using artificial chemicals may mean a reduction in input costs, it may also mean more physical work in weed control. In addition, it may mean that it is not possible to ‘push’ trees to their production limits using highly soluble fertilisers. Organic agriculture is not old-fashioned farming or hippie gardening but an agricultural system that combines the best natural methods with the best of modern science. Biodynamic agriculture was developed by the Austrian philosopher Rudolf Steiner in the 1920s. The aim in biodynamic agriculture is to treat a farm as a living system. The main farming principle is maintaining a healthy living soil by developing life-giving humus out of dead organic material. This involves using the horn preparation ‘BD500’ and other soil and plant activators. Another biodynamic principle is working to increase the cosmic formative forces that enhance plant and animal health and growth. Biodynamic farmers plant and harvest according to the phases of the moon.
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Can all tree nuts be grown organically? While all types of tree nuts can be grown organically, some nuts are easier to grow organically than others due to their particular susceptibility to pests and diseases. The key to successful organic production is selecting a site that optimises tree growth and nut yield and minimises pressure from pests and diseases. Another important factor is selecting varieties that show greatest resistance to pests and diseases. In most situations it is wise to learn to manage a small organic plot before converting a large orchard to organic management. Approved commercial organic fertilisers are available but where large quantities are required, on-farm compost making may be more cost-effective. On-farm composting of manure and plant waste requires heavy machinery including a front-end loader and manure spreader. Other essential machinery for organic orchards are mowing and mulching equipment. As one organic macadamia grower told me, the first thing you need to do when you manage an organic orchard is to go and buy a big mower. However, before deciding to become an organic producer, it is essential to research the market for organic nut product.
Why grow nuts organically? The three main reasons for growing nuts organically are: Economics. There is an increasing demand for organic produce and premium prices can be obtained. However, this premium price is crucial because yields in the short-term may not be as high as they can be under conventional production. It has been reported that a drop in income may be experienced during conversion to organic farming. Personal beliefs. Organic growers believe that growing nuts organically is more environmentally friendly due to the absence of toxic chemicals, reduced water usage and nutrient run-off and that organic agriculture is more sustainable in the long-term. Lifestyle. Organic growers prefer not to use artificial chemicals for health reasons and prefer to grow produce using natural methods. Food quality. Many people only eat food that is free from artificial chemicals. As well as being free from artificial chemicals, there is some evidence that food grown organically may be more nutritious than food that is grown by conventional methods.
Organic certification To ensure produce offered for sale as organic produce is grown and processed according to approved organic methods, organic farms must be certified by an approved organic body. Organic certification involves thorough inspection by a certifying body to ensure the farm complies with the approved standards. In addition to the initial certification fees, there are annual fees associated with maintaining organic status and these can be very costly for small-scale operations.
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Growers who intend to grow nuts organically can select land specifically for organic production and gain certification before planting begins. This has the advantage of ensuring the site and planting stock is suited to organic production. Alternatively, an existing orchard can be converted from conventional production to organic production. Certification is gained after a certain period of compliance. Although not strictly ethical, some growers convert to organic production when the trees are nearing production. This bypasses the difficulty of non-chemical weed control around young trees. Seven organic agriculture bodies are accredited certifying bodies by the Australian government through the Australian Quarantine Inspection Service (AQIS). The bodies accredited for production include: the Biodynamic Research Institute; Biological Farmers of Australia; National Association for Sustainable Agriculture Australia; Organic Growers Association; Tasmanian Organic Dynamic Producers; Organic Food Chain, and Safe Food Queensland. The National Standard for Organic and Biodynamic Produce was implemented in 1992 and developed by the industry in cooperation with AQIS. The National Standard allows access of Australian organic produce to the European market. The Organic Federation of Australia was developed in 1998 to promote greater adoption and consumption of organic and biodynamic food and fibre. There are two different levels of organic certification available to producers: Organic.
This is the top level or fully organic level.
In Conversion to Organic. This is the level for produce from farms in the process of being converted to organic status. Farms in this level are not considered organic until they have been farmed organically for about two years.
Planning an organic orchard Factors to consider when selecting land for organic production include: Climatic suitability. To minimise incidence of fungal and bacterial diseases inland areas that experience low humidity and lack of summer rain are chosen for deciduous nut trees particularly almonds, pistachios, walnuts and hazelnuts. Other climatic factors that can affect production of some types of nuts are freedom from frosts at and after flowering, excessive high temperatures during fruit development, rainfall during or before harvest, and damaging winds. Water supply should be adequate in quality and quantity. Soil suitability. Soil should have good drainage to minimise root problems but adequate moisture holding capacity to minimise the need for constant replenishing of nutrients and water. Detailed soil tests should be carried out to ensure the soil is free from chemical residues, pesticides and heavy metal contamination, and to ensure the soil type, soil pH, soil profile, nutrient status and biological activity is favourable. Biological soil analysis is available through the Soil Foodweb Institute, a laboratory that provides microbial assays of bacterial and fungal biomass, protozoa and nematode numbers and mycorrhizal root colonisation.
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Neighbouring properties. To reduce chances of contamination, select land that is remote from operations where there is heavy chemical usage. Other neighbouring features to avoid are heavy weed infestations and high populations of vermin that may damage trees or crops. Access to organic orchard and crop requirements. It is helpful to be situated where there is easy access to a supply of organic fertiliser and mulch material, and availability of orchard machinery, transport, processing facilities and markets. Factors to consider before planting include: Layout. For weed control purposes it is necessary to plant trees on the square so that the orchard can be mown both down and across the rows. Tree spacing should be adequate to ensure good air circulation and irrigation fixtures should be positioned so that they do not obstruct mowing operations. Planting alternating small blocks of each variety can also reduce the incidence of pests and diseases. Soil improvement. Before planting it is advisable to build up nutrients and organic content in the tree lines and eliminate all persistent weeds. This may require one or two years of preparation and include cultivation of green manure crops. Establishing a final ground cover of suitable legumes and grasses before trees are planted will ease maintenance and be beneficial to growing trees. Windbreak. To ensure wind is minimal when trees are young, plantations of suitable shrubs should be established well before nut trees are planted. Windbreaks also provide habitat for bees and beneficial insects and reduce dust. Varietal selection. Select the type of nut tree that best suits the local conditions then select the cultivars and rootstocks that are most disease resistant and best able to resist pest damage. While these varieties may not be the highest producers, natural tree health is paramount in an organic management system where artificial chemicals are not permitted. Varietal selection should also take into the market demand for each variety.
Managing an organic orchard While artificial chemicals are used to solve many weed, pest and disease problems in a conventional orchard, this is not permitted in an organic orchard. Organic growers must adopt clever techniques to develop optimum soil structure and fertility and solve problems by physical means or by approved chemical means. To be most effective, growers should develop a thorough understanding of the life cycle and habit of all weeds, pests and diseases that occur, and observe the most effective means of prevention and control. Therefore, it is wise to record the timing, nature and results of all management practices.
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Weed control One of the most labour-intensive operations is controlling the growth of pasture and weeds around trees. Weed management around young trees is particularly important as the trees are easily dominated by weeds. However, weed growth around young trees is most vigorous because the orchard floor is unshaded. Weed control is most time consuming in high rainfall regions. Methods to reduce weed growth in an orchard include: Mulching. Young trees should be mulched with a thick layer of weed-free organic material to suppress weed growth. The bonus is that this mulch improves soil structure, biological activity, moisture holding capacity and nutrient content of the soil. Be sure to keep the base of the trunk clear of mulch to prevent collar rot. Mowing the ground cover vegetation or inter-row crop in an orchard using mowers that throw the cut turf onto the tree root zone, will increase the organic material under the tree. Where nuts are to be ground harvested, mulch under mature trees may obstruct harvest equipment and contaminate the crop, so it should not be applied near harvest time. The source and contamination level of the organic mulch material must be approved by the organic certifying body before use. Weed growth can also be suppressed by weed mat material but this is not usually effective in the long-term. Mowing and brush-cutting. Slashing or mowing is the most frequent method used to control growth of ground cover vegetation in an orchard. While tractor-mounted slashers or mowers can be used down the inter-row, mowing close to the trees is best done with a smaller more maneuverable mower to reduce the risk of tree damage. To avoid leaving un-mown strips down the tree lines, organic orchard trees are usually planted so that the orchard can be mown both down and across the rows of trees. Brush-cutters can be used around trees if tree trunks are protected with solid guards. Irrigation emitters should be cleared of plant growth frequently but this is difficult to do mechanically without damaging the emitters. Thermal weeding. Killing weeds and ground cover growth by heat is permitted in organic orchards. Flame weeders that burn the growth must be used with caution especially during dry weather when growth and mulch material is highly flammable. Steam weeders are also used as an organic weed tool but as with flame weeders, great care should be taken around the tree trunk and root zone to prevent heat damage to the tree and plastic irrigation equipment. Solarisation. A pre-planting measure is to cover weeds growing in the area to be planted with sheets of plastic. The sheets are left so that the heat from the sun kills or ‘burns off ’ the weeds and ground cover vegetation. The plastic is then removed. Hand weeding. The safest method of weeding around the base of trees and irrigation equipment is by hand or by using a hoe.
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Grazing animals. Sheep and geese can be introduced into the orchard to assist with weed control. However, they can prove more trouble than they are worth because trees and irrigation equipment are easily damaged. Electric fences and tree guards can be installed to control grazing animals and protect trees from livestock but these are difficult to make completely animal-proof. Geese can be introduced to graze the ground cover vegetation in the nut orchard.
Tree nutrition The aim of organic nutrient management is to feed the soil thereby minimising nutrient inputs and nutrient losses from the soil ecosystem. When fertilising the orchard, organic growers aim to build up soil fertility, increase humus content and stimulate biological activity in the soil. The release of nutrients for plant uptake may therefore be a slow process. A nutrient budget that analyses the inputs (applied fertilisers, mulch, sod, nitrogen fixation) and losses (crop removal, leaching, volatilisation) from an orchard system allows growers to identify potential nutrient requirements. This analysis should be used in conjunction with soil analysis, fertiliser application records and the recommended nutrient requirements for the particular crop. To prevent contamination of the crop, organic fertilisers should not be applied to mature trees less than two months prior to harvest. Fertilisers used by organic growers include: Animal-based fertilisers. Animal manure such as chicken manure must be composted before use to reduce the risk of introducing diseases, antibiotics, or synthetic hormones to the soil and also to stabilise nitrogen. Un-composted manures may be permitted for use in the decomposition of green manure crops or straw. Blood and bone meal, meat meal, hoof and horn meal and fish waste are also permitted if the supply source is checked to ensure they are not contaminated. A compost made from four parts untreated saw dust or wood shavings to one part poultry manure is popular with many growers. The steaming heap is turned using a front end loader and the temperature in the heap is monitored to ensure it reaches the required 60°C. °C. C. This ensures unwanted bacteria and weed seeds are killed. Commercially prepared ‘organic fertilisers’ are permitted only if they are 100% organic. Plant-based fertilisers. Like animal based fertilisers, plant fertilisers are more effective when composted rather than applied fresh. In organic nut orchards, waste hull that is
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stockpiled after harvest is a ready source of material to mix with animal manure for composting. Green manure crops grown in the inter-row and incorporated into the soil also provide a valuable source of organic material and nutrient. Approved plant waste sourced from food and textile processors can be composted and added to the soil. Mushroom compost can be used if the source is approved. Seaweed, seaweed meal and pure seaweed products are permitted and make excellent organic fertilisers. Mineral fertilisers. Rock products may be added directly to the soil or added to compost heaps. The release of nutrients in rock products is accelerated by moisture, high temperatures and high biological activity. Where phosphate is required, ground phosphate rock may be applied and when calcium and magnesium is required dolomite may be applied. Ground untreated limestone and wood ash is also permitted. Gypsum of certain origins is permitted for soil conditioning purposes. Feldspar and potashbearing granites can be used as a source of potash, and ground granite and basalt provide a good range of minerals. Certain forms of trace elements can be applied with special permission. Activators. Approved organic bio-stimulants made at home or commercially prepared may be applied to stimulate biological activity in the soil. These include herb-based activators such as nettle tea, seaweed based liquids, wormcast juice, commercial organic preparations and biodynamic preparations.
Macadamia hulls can be composted for use as an organic fertiliser.
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Pest and disease control Ensuring a vigorous healthy crop is the best insurance against pests and diseases. However, approved chemical means of control are available for certified orchards but they must comply with allowable inputs under the organic standards. Fungicide/ bactericide preparations and certain insecticide products permitted for pest control include diatomaceous earth, quassia, soft soap, white oil emulsion and herbal preparations including natural pyrethrum. Products approved for disease control include sulphur, lime sulphur, copper sulphate, sodium silicate, herbal preparations and seaweed extracts. Details of all approved chemical preparations are available from the organic certifying body. To be most effective they should be applied after taking into account the level of disease, existing weather conditions, most effective concentration of the preparation, and the most effective method of application and timing of application. These common sense strategies are also applied in Integrated Pest Management (IPM), an approach used generally in horticulture to minimise chemical usage and ensure control methods are most effective. While the above products are permitted as pest and disease control agents, the aim is to develop management techniques that reduce dependency on these agents. Cultural practices that can be employed to reduce the impact of pests and diseases are numerous. Disease incidence can be reduced by ensuring good air circulation by judicial pruning, tree thinning and controlling ground cover vegetation. Humidity can also be reduced by use of drip irrigation instead of sprinklers. The wetting pattern of all irrigation emitters should be checked to ensure trunk and foliage is not wetted. Excessive wetting around the trunk and root zone can cause root and crown rot while wet foliage can increase incidence of fungal and bacterial disease. Dust can increase the incidence of mites and insect pests and practices to reduce dust in the orchard include ensuring permanent ground cover vegetation, reducing the passage of vehicles and sealing nearby road surfaces. Other cultural practices to reduce the impact of pests include the growing of a decoy crop and removing contamination sites such as broken branches, fallen nuts and other debris. Biological control methods are valuable in organic pest and disease control. Many of these methods use natural predators of the particular pest or disease. A particularly successful biological control program has been conducted at Stahmann Farms pecan plantation in New South Wales where pest insects including green vegetable bug have been controlled by introducing predator insects. Many predator species occur naturally and incorporating plantings of native vegetation into the farm plan to attract predatory insects and birds assists natural pest control. Biological control agents for certain nut crop pests are available from laboratories that specialise in biological control techniques. Mechanical control methods are also employed in nut orchards to reduce pest damage. These include light traps and sticky boards to trap flying pests, scaring devices such as gas gun and electronic bird scarers, and net covers to keep out birds.
Harvest and processing Tree nuts such as almonds, cashews, chestnuts, hazelnuts, macadamias, pecans and walnuts are harvested off the ground while pistachios are harvested by shaking into
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catching canopies. All nuts marketed as dried nuts are dried immediately after harvest before grading. Nuts such as chestnuts and fresh pistachios that are marketed fresh are immediately cooled after harvest before grading. The techniques used in the harvest and nut processing operations must comply with the standards set down by the certifying body and processing must be conducted in an approved facility. This includes cracking plants where nuts are sent off-farm for processing. While there is a perception that it is permissible for organic produce to look less clean than non-organic produce, there is no reason that this should be the case and the same low tolerance to marked or damaged nuts should be applied when grading. Second grade produce should be processed into value added products. The source of packaging materials should be checked to avoid risk of contamination. Produce labels should comply with the standards set down by the certifying body.
Markets The demand for organic produce reflects the number of farmers supplying the particular product and the number of consumers wanting to purchase that product. Markets accessed by organic producers include local farmers markets, organic wholesalers and distributors, organic retailers, organic agents at city markets, organic produce cooperatives, and mail order. Before selling through large wholesalers and exporters, it is sensible to find out what the payment arrangements are and check with the Marketing Authority to ensure the agent/wholesaler is an approved business. To comply with organic certification growers must accurately record all practices and procedures undertaken in the growing and processing of the product.
Further reading Kinsey, N., and Walters, C. (1999). ‘Hands-on Agronomy (soil fertility and plant nutrition).’ (Acres: USA.) Laffan, J. (2000). Organic Farming: Soils, crops, fruits and vegetables. (NSW Department of Agriculture: Orange, NSW.) Lampkin, N. (1990). ‘Organic Farming.’ (Farming Press Books and Videos: Ipswich, UK.) NSW Department of Agriculture (2004). Organic Fruit Production. Agnote DPI 190. Proctor, P., and Cole, G. (2002). ‘Grasp the Nettle.’ (Random House: New Zealand.) Wilkinson, J. (2002). Growing macadamias organically. Australian Nutgrower, 16(2), 38. Wood, D. (2002). ‘Organic Horticulture Starter Kit.’ (Saphire Coast Producers Association: Bega, NSW.) Zimmer, G. (2000). ‘The Biological Farmer’. (Acres: Australia.) In addition, websites to all organic certifying bodies are most informative.
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8 Success in business
Early research saves problems later The key to success in any new business venture is thorough research and when it comes to a horticultural project such as nut production, the research is extensive. There are cultural considerations and financial considerations as well as personal considerations. In making the decision about which crop to grow the first information you need is horticultural information. Find out as much as possible about all types of nuts, their cultural requirements, water requirements, pest and disease problems and every other aspect. A good start when gathering cultural information is to access as many relevant websites as possible, read as many books and research papers as possible and talk to technical experts and experienced nut growers. Once questions relating to site and nut variety requirements are answered, and the quest has narrowed down a particular nut crop, the next step is to join the relevant nut industry association. The various nut industry associations may have literature available to members that is not available to the general public. This may include an estimate of production costs, yields and farm-gate prices. Most associations conduct farm walks and seminars offering practical and technical information. Visiting other nut farms and talking to other growers also gives you a better idea of whether growing nuts is as you thought it would be. Of course one must take into consideration that no two orchards are the same. Having a good knowledge of markets is as important as having a good knowledge of the cultural requirements because there is obviously no point in growing nuts commercially unless you can sell them. Market information may be obtained from the nut industry body, from market analysis studies and through personal exploration of local retail outlets, wholesalers, processors and export opportunities. A thorough knowledge of current nut promotion programs, consumer demands, market trends and value-added products is also important.
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Research must also consider grower access to appropriate technical services and machinery support as well as processing requirements and facilities. In an area where a particular nut is widely grown, support services are likely to be good but these services are seldom available where the location is remote from a popular nut-growing region. Finally, and most importantly, is the research into the economic feasibility of the orchard. It is worthwhile seeking as much advice as possible from financial advisors, particularly advisors experienced in primary production.
Be serious about your purpose – lifestyle or business? The idea of growing nuts conjures up an idyllic life of working under shady trees and gathering beautiful nuts. Of course while these moments of glory exist, this is not the picture experienced day in day out on most commercial nut orchards where the working day can be long and hard and troubled by unforeseen problems. Indeed in making the decision to grow nuts, one has to be realistic and identify the actual purpose of the venture. If the nut orchard is to make a profit, it must be economically viable and to be economically viable it must be of sufficient size to justify the necessary capital costs particularly high-cost machinery and buildings. However, if the nut orchard is for retirement interest or as a part-time pursuit, then it may be wise to plant a small orchard of, say a couple of dozen trees that can be managed without the need for a range of expensive equipment. The key to success when developing a small cottage-industry-style orchard is to keep trees to a manageable number, bearing in mind that many of the management and harvest tasks will be manual and time-consuming. Small-scale orchards
An almond orchard in bloom (Wirthensohn).
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are the perfect solution for many part-time farmers and they can be lots of fun, a wonderful interest, and harvesting and marketing the product can be enormously rewarding as a family project. On the other hand, when deciding on a commercial nut orchard one must be realistic about personal ability in regard to available time, available finance, physical fitness and family support. What size orchard is appropriate for you, what income is required, is the orchard to be developed for investment purposes or is it a long-term farming project? Other questions that should be answered include what level of remuneration is required for the owner/developer’s time and whether the plan is to live on or outside the property? Management of a nut orchard is as time-consuming as you make it and it is easy to work day and night to get the jobs done. This of course is not practical and the project will soon become a burden. In fact many growers have found that having their orchard separate from home works well because it is easier to ‘switch off ’ after hours. Having the orchard site on a separate title also enables it to be sold as an operating business if and when the need arises, without disrupting the family home. Farms are like any other business and behind every farm gate there is a business structure in place to manage the financial affairs of the business. Before a new or additional orchard project is established there should be sound evidence that the operation has the potential to be viable. In addition, to be financially sound, an orchard business requires an appropriate level of equity, insurance against losses and attention to taxation law.
Ensure economic feasibility When conducting an economic feasibility study for a proposed orchard or orchard extension, information concerning all aspects of the orchard is required. A feasibility study should answer questions such as: What is the expected revenue? What resources are needed? What are the associated costs? How much profit will be made? It would also involve whole farm budgets and capital budgets, estimating yields, analysing profitability, assessing cash flows and risk factors. Be conservative in your estimates particularly in the number of years to production and yield per hectare. Farming is fun but it is not plain sailing because there are unpredictable elements to contend with, such as the weather, markets and government regulations. Having assessed the economic feasibility of a new project, a business plan should be prepared. This maps out the direction for the business and also forces one to sit down and think seriously about the reality of the business through the various stages of development. When applying for a loan, banks and other financial institutions require a properly prepared business plan. As with any business venture, a high level of equity is an advantage. There are alternative arrangements for owning and operating a business and advice from the home and small business associations would be useful. Advice also from an accountant experienced in primary production is essential in deciding the structure of the business — whether the business should take the form of a partnership, a company or a share-farm. There is no best arrangement and while a company structure may be financially and legally the most appropriate for one grower, a partnership may have tax advantages for another.
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Leasing an existing orchard or leasing land on a long-term basis may be an option worth considering. The land base and profitability of an existing orchard can be extended considerably by leasing neighbouring land. Leasing arrangements vary in regard to the level of responsibility for the lessee. In all situations, continually monitoring the financial status of a business is paramount if the business is to remain viable. This can be done by accurately calculating the gross margin, taking account of both obvious and hidden costs. If the gross margin reveals less profit than expected, an investigation can be made to determine possible solutions. It may be that the size of an operation needs expanding to become viable or it may be that costs can be reduced in certain areas, or management techniques can be changed to increase yield or market prices.
Taxation matters The rules concerning farm taxation are continually changing. To receive taxation benefits, all farming businesses must be judged by the Australian Taxation Office (ATO) to be in the business of ‘primary production’. For an orchard to be assessed as being involved in ‘primary production’, factors considered by the ATO include: the intention or potential to make a profit; the size and scale of the activity; whether the activity is carried on in a business-like manner; whether the taxpayer has previous experience in similar business activities, and whether the activity would be more properly described as the pursuit of a hobby or recreation. In addition to these criteria, it is an advantage if farm business records are accurate and include all farm income, and also if there is a regular time commitment to the operation, and the operation is well researched and has departmental guidance. The orchard, therefore, must be organised as a business and prove that it is a business to be classed as primary production for taxation purposes. Tax concessions available to businesses involved in primary production include ‘income averaging’, which permits primary producers to ‘average’ their taxable incomes over a five year period. The taxable income of a farm business is calculated by deducting the costs involved in production and maintenance and depreciation on capital items, from the gross income. Expenses involved in production and maintenance include wages and salaries to employees, hiring fees, power and fuel, insurance, bank interest, costs for repairs, running costs for office and orchard etc. Depreciation on capital items covers depreciation on structural improvements, machinery, office systems etc. A rebate is also available on the diesel fuel used for farm purposes. In July 2000 the ATO introduced significant changes with the introduction of The New Tax System. The main tax reforms this system introduced include a Goods and Services Tax (GST), Pay As You Go (PAYG) installments, the lodging of Business Activity Statements (BAS) and the requirement for all businesses to register an Australian Business Number (ABN). All businesses must be registered for GST in order to claim input tax credits for GST paid on things acquired in operating the business. In so far as the sale of nuts is concerned, unprocessed nut product is exempt from GST but valueadded nut snacks and baked products are subject to GST.
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The New Tax System also introduced changes regarding non-commercial losses. If you make a net loss in a business activity, you may, under certain circumstances, claim that loss by offsetting it against your income from other sources. Details of noncommercial losses are subject to change and up-to-date information should be checked with a tax accountant or accessed via the ATO website. GST on the sale of a property is not applicable when the farm is sold as a going concern; however, GST is applicable if the farming operation is not continued after the property is sold. Certain exemptions and/or rollover relief may be available to taxpayers depending on the past usage of the property and their future intentions for further business activities. Capital Gains Tax is applicable to the sale of properties if they were purchased after September 1985. The value of the farm improvements since the date of establishment or purchase is deducted from the sale value for Capital Gains Tax purposes. Thus, it is essential to keep accurate records of all improvements.
Insurance matters The purpose of insurance is to guard against losses caused by unexpected events such as fire, hail damage and accident. There are several types of insurance required when conducting a business such as an orchard. For instance, it is compulsory for employers to be covered by workplace injury insurance. It is also prudent to insure all items and structures critical to the operation, against fire and possibly theft. Crops can also be insured against crop failure. Public liability insurance should cover possible claims prompted by negligence on the part of the property owner. The possible claims could include claims from visitors for injury and claims from purchasers alleging belowstandard produce. Nut growers should practise self-insurance too by establishing fire breaks, maintaining machinery well, fitting safety protection on machinery and providing safety equipment and training for employees. Self-insurance also includes developing an emergency plan in case of flood, fire or accident. Specific advice should be sought from an accountant and insurance broker experienced in this area.
Management options Management of an orchard varies enormously according to the scale of the project. Small-scale orchards are often managed solely by the owner with extra help at harvest; larger orchards may be managed by a single orchard manager with seasonal assistance, while agribusiness projects may be managed by a team of specialist staff. Among the diverse range of management responsibilities, the three most timeconsuming orchard tasks through the year are irrigation, tree nutrition and pest control. The good management of these tasks largely determines crop yields and where the owner/operator does not have the time or knowledge for the on-going management in these areas it may be appropriate and cost-effective to engage an irrigation specialist to manage the irrigation scheduling. Similarly, it may be cost-effective to engage a
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horticultural pest specialist to manage pests and diseases in the orchard and a tree nutrition specialist to manage nutrition analysis and fertiliser application. One of the great benefits in growing a crop that is common to the area is having access to staff experienced in your particular crop, to skilled machinery contractors, processing and marketing facilities and transport. Being in close proximity to other growers also provides opportunities for sharing ideas and experiences. Engaging contract machinery operators to mow and control weeds in the orchard and harvest the nuts is particularly useful where the owner/operator is not mechanically minded or is without access to mechanical support. It also greatly reduces the capital cost when establishing an orchard and reduces the need for machinery sheds and machinery maintenance. Unfortunately problems can occur occasionally when hiring contractors and the contract work may not be as good or as timely as the owner/operator would wish. Where casual and permanent employees are engaged, employers should be aware of their responsibilities in regard to sick pay, holiday pay, accident insurance and superannuation. These responsibilities involve a degree of bookwork. Employee entitlements are subject to change and details should be checked with the appropriate department.
Developing a nut orchard in stages Developing a nut orchard in stages is essential for many projects but it is also sensible because each stage is undertaken as finance and time permit. For those new to nut production, staged development means the orchard grows with ones confidence and knowledge. It also means that over-capitalising can be averted if Stage 2 is not undertaken until Stage 1 is looking viable. In some situations Stage 2 can be financed from income from Stage 1 so that, in effect, the operation pays for itself. Before establishing a nut orchard, the first step a new grower should make is to plant some nut trees. These trees can be few or many in number, include different cultivars and rootstocks and they can be planted in a garden-type situation or nursery. The idea is to become familiar with the growth of your chosen nut tree and learn how best to manage the tree. These trees in time may become valuable mother trees for propagation purposes. The stages of development will be determined by the eventual size of an orchard. While it may be practical to plant all of a five hectare orchard in one season, larger orchards may be best established in blocks over a period of years. Planting only what is physically and financially possible at one time will ensure that full soil preparation and orchard preparation is achieved before planting. Very often, having learnt lessons from establishing Stage 1, changes are made in the establishment of Stage 2. A nut orchard is a long-term project but cultivation recommendations change in time. The most suitable varieties to plant also change as new cultivars and rootstocks become available. While nut trees are generally long-lived trees, yields and nut quality may decline after a couple of decades and replanting should be factored in to the orchard program.
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How many hectares should I plant? As mentioned in the section below on avoiding over-capitalising, the orchard should be of sufficient size to support the capital expenses incurred. As many growers discover, the equipment and facilities required to manage a two hectare orchard are little different from the equipment and facilities required to manage a 10 hectare orchard. Some recommendations suggest that 10 hectares is a minimum for the viability of certain nut crops while other recommendations suggest that 20 hectares is the minimum. This figure will vary according to tree density and will also vary from one situation to another, from one nut crop to another and from one region to another. Of course a nut orchard established on highly fertile land will most likely produce a crop earlier and yield better than an orchard established on marginal land. Another factor that affects the viable size of an orchard is the availability of contract harvesting equipment and outside processing facilities. This reduces on-farm expenses and in regions where contract growing arrangements are available, on-farm costs can be further reduced. While predicted yield figures are available for most nut crops, these should be used as a guide only and treated with caution. Seldom is it that conditions remain perfect for tree growth and nut production year in year out. Most importantly, the time taken to produce a harvestable crop varies, and yields, particularly early yields, can be quite variable between different cultivars. Finally, nut orchard establishment and management are incredibly complex and demanding and cutting corners may prove false economy. The most effective solution is to work within your particular limits regarding time and financial and physical abilities. In the long and short term, a well-managed 10 hectare orchard is likely to be more rewarding personally and financially than a poorly-managed 30 hectare orchard.
What machinery will I need? Like any farm operation, the equipment required to manage a 200 tree orchard is not a great deal different from the equipment required to manage a 2000 tree orchard. Similarly the equipment required to harvest and process the crop from 200 trees is not a lot different to the equipment required to harvest and process the crop from 2000 trees. The basic machinery essential in managing a nut orchard includes a tractor or tractors; mower, mulcher and herbicide sprayer for controlling growth on the orchard floor; air blast sprayer or sprayers for controlling pests and diseases; irrigation equipment; ground spreader and fertigation equipment for managing tree nutrition, and appropriate tree pruning equipment. Where birds are a pest, bird deterring equipment is also required. Then, of course, there is harvest equipment and because nuts are small in size bulk handling of the product is essential. Harvest methods vary according to the type of nut and the size of the orchard. For almonds, pecans and walnuts a tree shaker is essential and once on the ground the nuts are usually swept into windrows with a sweeper and picked up by a pick-up harvester. A tree shaker is not used when harvesting hazelnuts, chestnuts or macadamias but the nuts fall to the ground naturally. While hand harvest has been the norm for chestnuts in the past, chestnut harvest is now becoming mechanised. Hand
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harvest is seldom practical for macadamias and hazelnuts and mechanical pick-up machines are required. Pistachios are small in size and have an open shell so they are collected before they fall naturally from the tree. A tree shaker with catching frame is used and the pistachio nuts fall into the frame and are conveyed to a bin. On small orchards and orchards of young trees growers usually devise simple manual methods of harvesting nuts, however, manual methods are labour-intensive, physically demanding and very often do not enhance nut quality. From the harvester, some nut crops require hulling before drying. All nuts except fresh chestnuts and fresh pistachios are dried. This requires some form of silo or bin drying mechanism, and elevators to transfer the nuts from one operation to another. Nuts to be marketed fresh are taken from the harvester to a cool room. Both dried and fresh nuts must be graded before market, although on-farm size grading may not be required where nuts are sent straight from the drier to a processor. Nut grading machinery includes elevators, size graders, quality inspection belts and packaging equipment. Forklift equipment is also essential for transfer of nut bins and pallets. A machinery shed(s) are required to house orchard equipment and appropriate shedding is also needed for nut processing equipment. Machinery is an exceedingly costly but essential part of nut production. In large orchards, many of the nut harvest machines are sophisticated self-propelled units while in small orchards most machines used are tractor mounted. Purchasing secondhand equipment and having engineering skills to repair and modify equipment greatly reduces machinery costs.
Capital cost of orchard machinery is substantial.
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Avoid over-capitalising your investment While the financial status of each orchard project varies, ensuring the expenses incurred on capital items match the scale of the operation, avoids over-capitalising. Capital expenses may be reduced if land can be procured on a long-term lease; however, this is seldom an option. Minimising equipment purchases and using contract or hired machinery in the early development of a nut orchard may also be possible. The cost of planting stock varies according to whether the trees are propagated in situ or purchased from a nursery as ready-to-plant trees. One must factor in here the survival rate of trees and without appropriate expertise, propagating trees in situ may prove false economy. Hiring machinery or using contractors to carry out orchard maintenance such as weed control, may be the most economical solution in the early development of nut orchard. Using outside equipment and leaving the purchase of expensive capital items for one or two seasons will also mean the grower is more likely to purchase the most appropriate type of equipment. However, the purchase of some equipment is essential to orchard establishment. Equipment for irrigation, tree nutrition and canopy management is imperative for good tree growth. Frequent control of weed growth around the trees is also essential in a young orchard. Fortunately, high cost harvest machinery and processing equipment is not required until the trees are in production. The source of water supplied to an orchard varies from orchard to orchard. Water entitlements may be a saleable item until the trees require the full entitlement. Where a water storage dam is required, it may be possible to develop this storage in stages. Perhaps the safest strategy is to ensure the orchard is of sufficient size to justify all the basic capital expenditure required, to research your project thoroughly, and to enter the project with a high level of equity.
Ensuring early cash flow The better the management of young trees the sooner the trees will produce nuts. Time spent promoting trees to grow fast and develop a strong frame are the best investments one can make in a new orchard. If trees are well-managed it may be possible to achieve a harvestable crop in five years, while poorly managed trees may take 10 years or more. Of course, different types of nuts produce at a slightly different age. However, planting a large orchard of trees and trying to manage weed control, irrigation, fertilising and tree training on weekends, will not produce early cash flow or healthy trees. It is also true that the better the growing conditions are, the sooner the young trees will come into bearing. Where early cash flow is required, fertile soil, ideal climatic conditions and good management are essential. Unfortunately trees are unpredictable in growth rate, years to production and yields. There are no guarantees in farming and unexpected crop failure, damaging weather and market fluctuations are always possible. Tree spacing also affects cash flow. Where trees are planted 400 to the hectare, cash flow will be greater in the earlier years than it would if the trees are planted 200 to the hectare. Some growers choose to ‘double-plant’ trees and thin out some trees when overcrowding occurs. Inter-planting with a quick-producing fruit crop has also been tried.
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Growers can achieve an early cash flow before trees come into bearing by growing and harvesting a fodder crop such as clover or lucerne hay, in the inter-row.
Recording activities The day to day work on the farm can seem unimportant, but keeping a written or an electronic diary that records activities no matter how trivial they seem, is essential. It is almost impossible to remember exact flowering dates and irrigation scheduling through the season, or when and what fertilisers were applied or how trees were pruned, but this information is invaluable if we are to understand nut tree dynamics and learn how to improve production techniques. Weather should also be noted in farm records. It is useful to install weather monitoring devices such as a rain gauge and temperature data loggers that can be downloaded and a print-out made of the seasonal temperature fluctuations. This can be helpful later when assessing the reason for a particular pollination or nut quality problem. As well as providing accurate documentation, recording daily activities and observations also increases our awareness of what is actually happening, rather than simply making assumptions. Photographs are invaluable too in providing a record of orchard development and activities and they also provide a wonderful means of reflection. How else can we remember how much our trees have grown or appreciate how much work we have done, without recording their progress in pictures? Photographs also give a rewarding personal touch to the development of a nut orchard. Recording financial details are obligatory for any business and the business activity statements provided every quarter for taxation purposes helps to keep tabs on the current financial status. While being computer literate and familiar with business accounting software is not essential, having the business activity data on computer makes it readily available for other purposes, particularly funding applications. Where a grower is not able for time or other reasons to keep up to date with financial recording, the responsibility should be handed over to a bookkeeper or accountant.
Work to produce quality Working to produce quality nuts begins before the trees are planted. Both site selection and selection of appropriate cultivars and rootstocks is the first step on the road to nut quality. Good management of young trees develops strong healthy trees and minimises the time to nut production, and good management of bearing trees is usually rewarded by good yields and nut quality. There is little point in growing sub-standard product that is difficult to harvest, time-consuming to process and difficult to market. Indeed, good management is good investment and producing quality nuts is not only financially rewarding, it is personally rewarding and beneficial for the whole nut industry.
Further reading Australian Nut Industry Council website http://www.nutindustry.org.au Australian Taxation Office website http://www.ato.gov.au ‘Fact sheet ‘Non-commercial losses’.
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9 Almonds
Background The almond tree grown today originated from wild almonds growing in deserts and low mountain forests of central and south-west Asia from northern Syria and Turkey, to Iran and Iraq. From the bitter-seeded wild forms a sweet nut was selected and cultivated some 4000 years BC. Thousands of years later in the mid-1800s almonds were first cultivated as a commercial nut crop. In the years between 1965 and 1985 commercial almond plantings in Australia increased by about threefold and improved varieties and technology produced greater yields. Increases were profound too in the United States with great expansion of the cultivation regions in California. Plantings also increased in other almond producing countries including Spain, Italy, Greece, Morocco, Turkey and Portugal. Today the United States accounts for approximately 80% of world almond trade and produces more than half of the world almond supply. The next highest producer is Spain. Almond production in Australia was originally concentrated around the Adelaide region, but since the 1960s production has moved to regions further east along the Murray River and the average size of almond orchards has greatly increased. While some orchards remain in the Adelaide area near Langhorne Creek, Willunga, Angle Vale and Virginia, the main almond growing areas extend from Nildottie north-east of Adelaide in South Australia up the Murray River as far east as Boundary Bend in Victoria. Within this area the vast majority of almond orchards are located from Waikerie to Renmark in the Riverland, and from Mildura to Nangiloc and Robinvale in the Sunraysia region of Victoria. Almond orchards are also scattered in New South Wales at Finley and Darlington Point. Improved economy of scale in recent years accompanied by increased yields and the promotion of nut health benefits has led to the increasing attraction of almond production as an investment. The new enlarged industry base should provide increased funds for research and development.
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In 2004 Australia produced some 10 300 tonnes of almond kernel and while this is substantial, it is not large on a world scale. However, the Almond Board of Australia expects that by 2008, as new trees come into production, the national crop will double. The Almond Board of Australia is the industry body representing growers and processors and is based at Berri in South Australia. There are almost 200 members and levies provide funds for promotion and research programs. One of the current research programs is an Almond Management Trial and this has successfully shown that yields can be increased using improved orchard management techniques.
Botany The botanical name for almond is Prunus dulcis, however, this nomenclature has been challenged in recent years. Almond belongs to the same genus as cherry, plum, apricot, peach and nectarine. It is a deciduous tree with strong primary branches growing several metres tall in favourable conditions. In cultivation the tree rarely grows higher than five metres. There are two types of almonds: sweet almonds that are grown for their edible nuts, and bitter almonds that are grown for oil of bitter almond. The almond trees grown commercially are hard and soft-shelled varieties of sweet almond. Almonds belong to the Rosaceae family and therefore bear rose-like flowers with five white petals that are pinkish at the base. Almond trees have a leafy canopy through the growing season. The leaves are narrow and tapered with a glossy upper surface and slight indentations along the margin. Flower buds and leaf shoots emerge in late winter and early spring. Almond flowers are insect pollinated, primarily by bees. After fertilisation, the ovary at the base of the flower expands to form a fruit. The hull covering the fruit is velvety and soft green and as the fruit matures, the seed, shell and hull tissues differentiate. At full maturity the hull splits and the whole fruit falls to the ground.
Almonds belong to the rose family and the flower has a rose-like appearance.
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Almond fruit is covered in a green velvet hull.
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Specific requirements Soil Almond trees grow best in well-drained sandy loam. Good drainage is essential, so shallow clay topsoils over heavy clay subsoils are not suitable. Deep ripping is advised where a hard layer under the topsoil creates a physical barrier. Very sandy soils can be unsuitable due to wind erosion and poor retention of moisture and nutrients. If sandy soils are to be planted they should be improved before planting with the addition of large amounts of organic matter and regular mowing of ground cover vegetation to increase organic content. Almond trees prefer soil with a pH close to 7, but wider tolerance is extended by rootstock selection. Limestone layers are a problem in many almond growing areas and should be avoided where the top half metre of soil exceeds a pH of 8. Almonds are sensitive to saline soils and saline irrigation water. However, research in California indicates that growth and production are not impaired on soils having a salinity level less than 1.5 dSm–1 (the electrical conductivity of irrigation water is expressed in deci Siemens per metre at 25°C (dSm–1)) in the USA, and when irrigated with water that has a salinity level less than 1.1 dSm–1. This research is based on the premise that irrigation allows for sufficient leaching to prevent salt accumulation in the soil. A complete soil analysis is always recommended before planting. (See Chapters 2 and 4 for more cultivation details.)
Climate Winter chilling. Almond trees require a period of winter chilling to ensure good flowering and spring growth. While chilling requirements vary slightly with the almond variety, 300–500 hours of chilling below 10°C is required for commercial production. Frost. Frost is one of the greatest risks to almond crops especially during flowering and early fruit development in the late winter and early spring period. The sensitivity of almond flowers to frost increases as the flower matures and light frost at petal fall may decimate the crop. A moist soil decreases the severity of frost and irrigation via undertree sprinklers is often applied to reduce frost damage. The safest strategy, however, is to avoid planting in valley locations prone to air drainage and frost in late winter and early spring. Air drainage is a term that refers to a flow of cold air moving down a slope and creating a frost zone in the valley below. Humidity. Almond trees are susceptible to disease in humid conditions. Low humidity and dry weather particularly from spring to autumn, is essential for commercial almond production to keep disease pressure at a manageable level. Dry sunny weather at flowering also enhances bee activity and fruit set. A rain-free period in summer and autumn is crucial for the ripening fruit, and also for harvest to achieve nut drying and ensure nut quality. Hence almonds are best suited to inland areas where the growing season is dry.
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Water requirements. Because production of quality almonds requires a hot dry climate, there is a high requirement for irrigation during the growing season. The amount of water required varies on the locality and age of tree but as much as 14 Ml ha–1 has been quoted as an annual requirement for optimum production. Shelter. Strong wind is detrimental to both tree growth and nut set. Wind breaks should be established before planting as young trees are most susceptible to damage. Temporary windbreaks may be adequate and a crop of quick-growing sorghum between orchard blocks is an effective short-term windbreak. Although an orchard creates its own shelter when the trees are established and canopies are dense, branches on bearing trees are prone to wind damage when the crop load is heavy.
Location Like other nut crops, almond orchards are highly mechanised and the site should be reasonably level for easy management. Level sites are also required for bee hives during flowering. For efficient production, supply of bee hives should be easily accessible. The location should also have easy access for harvest contractors if required, processing facilities and markets. Nut-eating birds such as cockatoos, parrots and ravens can decimate an almond crop and require vigilant control. Orchards should therefore be isolated from residential areas to prevent problems with neighbours due to noise of bird deterrents and also machinery noise and chemical use.
Flowering and pollination The time of flowering depends on exposure to chilling and the warm weather that follows. Growth of flowers and first leaf shoots is made possible by the food reserves in the shoots and spurs. Because there is competition between flowers and leaves for food and moisture at flowering, a high fruit set may result in less foliage growth and vice versa. A heavy fruit set may also mean reduced nut size. Almond trees can become biennial bearing. Early spring frosts and wind and rain at flowering reduce pollination success and result in low yields. Fine sunny weather at flowering is therefore most desirable for optimum insect activity and fruit set. The honey bee is the most important pollinating insect and bee hives are brought into the orchard just before flowering. Banks of hives are placed in strategic positions through the orchard and maximum bee activity is reached when day temperatures reach about 21°C. A rate of at least six two-storey hives per hectare of orchard is recommended in commercial orchards. Bees usually forage no further than a kilometre from their hive and when blossom is abundant, this distance may reduce to 500 metres. However, groups of hives are best located approximately 100 metres apart in direct sun to maximise bee activity and bees must be provided with clean water close to the hive. It is safest to refrain from chemical spraying in the orchard during flowering. Bees transfer pollen from one flower to another flower. As almonds require crosspollination, the pollen must be transferred from the anthers of a flower of one variety to
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the stigma of a flower of another variety that is compatible. To be compatible the pollen must have the ability to result in fertilisation of the ovule. While there are some selffertile varieties available (i.e. the pollen of a flower has the ability to fertilise the ovule of the same flower) these varieties are not used in commercial production in Australia at this stage.
Beehives are brought in to the orchard to maximise pollination (T. Monson).
To maximise fruit set, it is essential to interplant the rows of main crop variety with a polliniser variety or varieties. A polliniser must be genetically compatible and show coincidence of flowering. The most common commercial main crop variety is Nonpareil and included with Nonpareil are one or more pollinisers such as Carmel, Price, Peerless, Ne Plus Ultra, Fritz and Mission. Bloom times of all varieties may vary according to location and season.
Orchard layout Tree rows in an almond orchard are usually about 6.5 metres apart to allow adequate machinery access. Tree spacings within the row are usually one to two metres less than the row spacing. However, there are many variations from widely spaced orchards of 7.2 m × 7.2 m giving 193 trees per hectare to orchards of 7.2 m × 3.6 m giving 386 trees per hectare. The usual ratio of pollinisor to main crop varieties is 1:1, however, two pollinisers are often included to ensure pollination if a polliniser fails to bloom well. Orchards usually comprise 50% Nonpareil and 50% polliniser A, or 50% Nonpareil and 35% polliniser A and 15% polliniser B. The pollinisors selected can include one pollinisor that blooms
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slightly earlier than the main crop and the other pollinisor slightly later than the main crop variety. The more synchronised the blooming is, the greater the fruit set should be. It is usual to plant pollinisors as a complete row to ease management and allow separate harvesting of each variety if required.
Almond cultivars A cultivar is the name used to describe a cultivated variety. Cultivars are selected for favourable characteristics including nut quality, tree growth and disease resistance. Almond cultivars can be grouped according to the type of shell: papershell has crumbly shells, soft shell has a soft but not crumbly shell, and hard shell is tough and difficult to open by hand. The main cultivar grown in Australian orchards is Nonpareil because the nut is favoured in the marketplace. Other varieties that bloom at the same time as Nonpareil are grown as pollinisors. Nonpareil is used as the industry standard. In the past, almond trees did not produce harvestable crops until at least year four but today trees usually produce a harvestable crop by year three due to improved growing techniques.
Some almond cultivars Butte. Semi-hard shell; excellent crop potential; late bloomer; pollinisor for Mission; spreading tree; small kernel size. Carmel. Papershell; popular pollinisor for Nonpareil; medium upright tree; high yields when young; long attractive kernel; late harvest. Fritz. Semi-hard shell; good cropper; once favoured pollinisor for Nonpareil but now not popular due to susceptibility to bacterial spot; kernel plump and shiny; upright vigorous tree; very late harvest. Mission. Hard shell; good cropper; medium-small but plump kernel but unsuited to blanching; late bloomer so avoids frosts; vigorous tree when young; upright branches; late harvest. Monterey. Soft shell; very good crop potential; late harvest; large long dark kernel; may produce double kernel. Morley.
Semi-hard shell; late flowering; medium small kernel.
Ne Plus Ultra. Soft shell; early bloomer; good cropper; large kernel but many doubles; smallish tree with spreading branches; susceptible to some diseases and not in favour. Nonpareil. Papershell; good consistent cropper; high shelling percentage; good flavour; medium size attractive kernel favoured by markets; poor shell sealing that may allow kernel staining during rainy seasons; large vigorous tree; early blooming and the industry standard against which others are compared.
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Padre.
Hard shell; good consistent cropper; medium small kernel.
Peerless. Hard shell; early bloomer and susceptible to frost; popular pollinisor for Nonpareil but limited market for kernel as it is variable in shape; nut sold as inshell. Price. Papershell; good cropper but tends to be biennial; popular pollinisor for Nonpareil; medium small kernel but many doubles; poor shell seal; nuts tend to form in clusters. Sauret #1. Poorly sealed papershell; good cropper; flowering similar to Nonpareil; elongated kernels. Sonora.
Papershell; medium large kernel; good cropper but tends to biennial bearing.
Almond rootstocks The almond cultivars desired for nut production are propagated by budding onto a suitable rootstock. The choice of rootstock is determined by the type of soil in the orchard and disease pressure of the locality. The rootstock is grown in nursery beds and the cultivar is budded when the rootstock is of suitable size.
Rootstocks Nemaguard peach. This rootstock is a cross of the common peach (Prunus persica) and Chinese peach (Prunus davidiana). It is propagated from seed and is popular because it is resistant to two common species of root knot nematode that can be troublesome in sandy soils. Trees on Nemaguard are vigorous but they do not tolerate poor drainage and they do not tolerate salt or lime in the soil. A lime-free depth of 800 mm is recommended. Peach × almond hybrid. To achieve this peach/almond cross, Nemaguard is often used as the peach component to introduce nematode resistance. This hybrid rootstock can be grown from cutting or tissue culture. It is a popular rootstock because it is very vigorous, it has deep roots, and shows drought tolerance and some tolerance of saline soils and limey soils. However, it does not tolerate poor drainage. Seedling almond. While this rootstock lacks the vigour of the two hybrids above, it is deep rooting and shows drought tolerance so it is a good choice for unirrigated orchards. It grows to a moderate sized, long-lived tree. It is known to be tolerant of lime and is reported to grow in soils with a lime-free depth of only 400 mm. However, seedling almond rootstock has no resistance to root knot nematodes that may occur in sandy soils.
Propagation Almond seed for rootstock use is stratified before sowing by placing the seed in moist sand or vermiculite in a refrigerator or coolroom. The required period of stratification
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varies according to the rootstock variety. Stratification time for peach seed is more than double that required for almond seed. After stratification, the seed is sown in nursery beds in early winter. When germinated, the seedlings are managed for maximum growth until late spring when they are budded. The cultivar buds are inserted as chip buds or T-buds (see Chapter 3 for budding details) at about 150 mm above the soil level on the south side of the trunk. The top growth of the rootstock is pruned back to stimulate bud growth and all sucker growth is removed. By the end of the growing season the trees should be well over one metre high. In early winter when the tree is dormant, it is dug for replanting in the orchard. It is always important to use virus-tested propagating material and ensure the identification of the variety is accurate.
Planting techniques Almond trees are planted during winter dormancy. Early winter is the best time because almond budburst can begin by late winter. After the soil is prepared (see Chapter 4), the irrigation system is installed and the orchard rows and tree spacings are marked out. In areas prone to crown gall, the bare-rooted trees are dipped in an anti-gall inoculant that protects them from Crown Gall. The roots of bare-rooted trees must be kept moist at all times during the planting process. The bud union should always be well above the soil surface after planting. Where rabbits are present and sunburn of the trunk is likely, tree guard sleeves are placed around the trunk at planting. The newly planted tree is headed back to a good bud at a height of about 900 mm. Purchasing quality nursery stock and subsequent good management of irrigation and fertiliser requirements will produce optimum tree growth. In many orchards, growers sow a crop of sorghum in the inter-row or every second or third inter-row, as a windbreak.
Newly budded nursery trees are managed for maximum growth.
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Tree guard sleeves placed around the trees at planting protect trees from rabbits and herbicide drift.
Management of young trees For maximum tree growth, weeds should be controlled regularly. This may involve a combination of hand-weeding around the trees and use of herbicide along the tree rows and around irrigation equipment. Adequate soil moisture and tree nutrition will ensure optimum growth. Frequent light applications of fertiliser produce best growth of young trees. While a high nitrogen fertiliser is commonly applied in a young orchard, an adequate balance of potassium is essential. Trials have shown remarkable growth rates from very frequent low-dose applications via a fertigation system. Tree training begins in the first growing season and further tree shaping is done during winter dormancy. Light pruning is recommended for young trees as it leaves a larger leaf area to support the growing tree. The aim is to maintain vigour and promote early fruiting. To form an open-vase shaped frame, four primary limbs are selected at a trunk height of 900 mm. Several secondary limbs are later selected at a height of about 1500 mm. Branches below 900 mm are removed to allow for mechanical harvesting. To promote fruiting, branches can be trained down to a more horizontal direction. Tree training is most successful when trees are growing vigorously. (See Chapter 6.)
Management of bearing trees Irrigation While the annual water requirement given for almonds lies between 1100 to 1400 mm a year, knowing when to water and how much water to apply is established by monitoring with soil moisture measuring devices. These devices are placed at different depths and the
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most active root zone depth is around 60 cm. While peak water demand in most almond growing districts is during December and January, spring and late summer moisture is also very important. An almond orchard is not irrigated for a short period prior to harvest to ensure a dry environment for falling nuts. Drip irrigation is the most efficient irrigation method for almonds and many drippers may be required per tree (depending on the capacity of the emitter) to ensure an adequate area of the root zone is watered. However, where watering of an inter-row cover crop is required, micro-sprinklers are more suitable. As the almond crop is ground harvested, it is important to install the irrigation lines and emitters in such a way that they do not obstruct harvest machinery.
Fertilising In a producing orchard the amount of fertiliser required depends upon many factors including the amount of nutrient removed from the orchard at harvest. A check of the nutrient status of the trees is established by conducting annual leaf analysis. Nitrogen and potassium are the nutrients most required in almond orchards and while any nitrogenous fertiliser can be used, urea or ammonium nitrate are often recommended. Application is most efficient through drip irrigation but ground application is also common. Nitrogen is applied before bloom, and during spring and summer. Commonly 200 kg of actual nitrogen per hectare is applied annually in a mature almond orchard. Leaf analysis has revealed that zinc is deficient in many almond growing areas and particularly in deep sands and shallow soils containing free lime. Zinc is most efficiently applied via foliar spray during spring. Superphosphate is applied in autumn and one application every few years has been sufficient in many orchards. To assess tree nutrient status, annual leaf analysis is recommended. Below is a guide to the desirable nutrient levels in almond: Element
Desirable level
Nitrogen
2.2–2.5%
Phosphorus
0.1–0.3%
Potassium
>1.4%
Calcium
>2.0%
Magnesium
>0.25%
Sodium
not >0.25%
Chlorine
not >0.3%
Boron*
30–65 ppm
Copper
>4 ppm
Manganese
>20 ppm
Zinc
not <15 ppm
* Critical values for boron deficiency and toxicity are being revised. Boron content of the hull >300 ppm is excessive. Leaf sampling is not effective to determine excess boron. Source of data: Micke (1996): 184, Table 5.4.
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Pruning Bearing trees are pruned as required to remove old wood and promote the production of new wood. The aim is to promote fruiting wood, allow light penetration into the canopy, maintain tree vigour and allow machinery access. Pruning cuts should be aimed at thinning branches and removing weak, crowded or badly shaped limbs. A clean trunk allowing efficient tree shaking is important to keep in mind. Long whippy limbs are more difficult for tree shaking than fully laden shorter limbs. Pruning should be carried out after harvest in autumn in dry weather to minimise the risk of disease. Some growers use hedging machinery to reduce the cost of pruning. Hedgers can be used to top the tree canopy and/or hedge the sides of the canopy but this will reduce nut yield the following season. Hedging is therefore not done on an annual basis and the long-term application of hedging is uncertain.
Pests and diseases Almonds are prone to a few pests and several diseases, particularly when humidity is higher than desirable. To minimise humidity, prune to maintain good air circulation, plant trees in locations of low humidity at wide spacings and use drip irrigation.
Pests Birds. Like most other nut crops, almonds are favourite food for birds, particularly ravens, parrots and cockatoos that can quickly decimate a crop unless bird control measures are put in place. (See Chapter 6 for control measures.) Bryobia Mite (Bryobia rubrioculus). This pest is more prevalent in dry dusty parts of an orchard. Leaves look pale from a distance and slightly mottled. Red powdery eggs can be found in the branch crevices from mid-summer to winter. Adult mites are tiny but can be seen without magnification. They differ from two-spotted mite by their long forelegs and absence of two spots. Control measures include reducing dust on traffic lanes and spraying trees with miscible oil during dormancy. Carob Moth (Ectomyelois ceratoniae). In spring and summer the grey adult moth lays eggs on nuts and particularly in mummies (nuts that remain on the trees through winter). The grubs bore into the nut and pupate. The moths hatch in spring to continue the life cycle. Moths can also emerge in stored nuts. This pest is reduced by practising good orchard hygiene, removing mummies and encouraging insect-eating birds into the orchard during dormancy. Curculio Beetle (Otiorhyncus cribricollis) and Fuller’s Rose Weevil (Asynonychus cervinus). These leaf-eating insects cause ragged edges on leaves of young trees and defoliation in bad infestations. The Curculio Beetle is brown and feeds at night. Fuller’s Rose Weevil is grey and feeds during the day. Spraying is usually not necessary.
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Diseases Anthracnose (Colletotrichum acutatum). This fungal disease infects developing nuts after fruit set and infected nuts may remain on the tree and show sunken orange lesions and subsequent gumming. Nuts are susceptible from the bud stage until harvest. Twig dieback also occurs and leaves may develop edge burn but remain attached. The disease is more prevalent in warm moist conditions and spores are spread by wind-blown water droplets. Chemical protection is routine in susceptible orchards. Bacterial Gummosis (Pseudomonas syringae). This bacterial disease causes wilting and death of trees or branches in early spring. It is more prevalent in cool humid sites. Infection can be caused through injury to the trunk and branches. Control includes pruning out infected wood and spraying with a copper-based fungicide at leaf fall and pre- and post-blooming. Bacterial Spot (Xanthomonas campestris). This bacterial disease results in holes in leaves like shothole, and gumming of nuts causing nut drop and ‘stick tights’ at harvest. Infection is spread via moisture such as wind-blown rain or irrigation spray. Bacterial spot can be severe in humid weather during summer and some almond varieties are more susceptible than others. Control is achieved by applying the recommended chemicals in conjunction with planting resistant cultivars, improving air circulation, reducing tree injury and removing infected material from the orchard.
Almond nuts showing lesions and gumming typical of Bacterial Spot (Scholefield Robinson).
Crown Gall (Agrobacterium tumefasciens). This soil or tree-borne bacterium causes galls to form on the tree roots and crown resulting in stunted growth and death of the tree. The tree may be infected in the nursery or in the orchard and it is most common in
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sandy soils. Crown gall infection can be prevented by dipping rootstock nursery seed before sowing and dipping bare-rooted trees before planting in anti-gall inoculant. Treatment can also be applied through the irrigation system. Hull Rot. This fungal disease can be caused by the fungi Rhizopus stolonifer or by the brown rot fungi Monilinia spp. Symptoms include death of shoots and spurs and nuts that are difficult to remove at harvest. It develops when there is rain between hull split and harvest and it can be severe where irrigation sprinklers wet the foliage. Hull Rot can therefore be minimised by improving air circulation in the canopy and reducing irrigation at hull split to ensure a dry canopy. Non-infectious bud failure (BF). This growth disorder is a genetic disorder and infection is transmitted via vegetative propagation. BF is also called ‘crazy-top’ and ‘muletail’ because bunches of shoots form at the tip of a branch. This symptom is particularly noticeable in early spring. Rough cracking bark on the branches can also occur followed by purplish cankers at the base of affected buds. Varieties such as Carmel and Nonpareil are more susceptible than other varieties and BF is more prevalent where summer temperatures are high. There is no control other than removing affected branches or affected trees and ensuring new trees are propagated from disease-free bud wood certified by the Almond Board of Australia. Rust (Tranzschelia discolor). This fungal disease causes yellow spots on leaves and rusty patches form on the leaf underside. Infection can result in defoliation and reduced tree health and it is more prevalent in moist weather. Control measures include spraying with recommended chemicals during the growing season and spraying post harvest with urea or zinc sulphate to defoliate the tree and prevent disease carryover. Shothole (Wilsonomyces carphophilus). This fungal disease results in small round holes in the leaves and gummy spots on the hulls causing the hull to stick to the nut. It is prevalent in wet weather and control measures include improving air circulation in the canopy, spraying with a copper-based fungicide at bud swell and after petal fall and also at leaf fall. Silver Leaf (Chondrostereum purpureum). This fungal disease causes leaves to develop a silvery appearance and it can be widespread in high rainfall regions. Trees may die eventually unless controlled. Control measures include removing infected material from the orchard, avoiding large pruning wounds, pruning only in dry weather and using a sealant on pruning wounds. Verticillium Wilt (Verticillium albo-atrum). This soil-borne fungus causes wilting of foliage in early summer and can remain in the soil for many years. Plants belonging to the Solanaceae family, such as nightshade, can harbour the fungus. Some varieties of almond are more susceptible than others. Infected trees may recover.
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Harvesting Almonds are the first of the tree nuts to be harvested beginning in late February for Nonpareil in some regions and continuing to mid April for late varieties. Harvesting is done by shaking the tree to ensure all nuts are down, allowing the nuts to dry, sweeping the nuts into windrows and picking up the nuts with a harvester. In preparing the orchard for harvest the floor is mown short or sprayed with a knock-down herbicide and cleared of branch debris and stones. Dry weather throughout the harvest operation is needed to avoid nut deterioration. When the hulls are splitting open and dry, the trees are ready for harvest.
Care of the bark on the trunk is important during tree shaking (Jubilee Almonds).
Before the trees are shaken, the inter-row is swept clean of nuts to ensure nuts from neighbouring varieties of almond are not mixed with the variety to be harvested. While tractor-mounted shakers can be used in small orchards most growers engage harvest contractors or own self-propelled shakers. Side-mounted shakers make the operation faster than front mounted shakers that have to back in and out to each tree. Care of the bark on the tree is important during tree shaking as bark damage can cause death of a tree or reduced tree health. Tree trunks are shaken and the fallen nuts mostly remain in the hull. The crop lies on the ground for a few days until it has dried sufficiently to prevent deterioration during storage. Fine weather therefore is essential to ensure quality kernel. Young trees that are too small for tree shaking can be knocked with a rubber mallet to bring the nuts down. When dry, the crop is swept into windrows with a sweeper. Most large growers use low profile self-propelled sweepers that fit under the branch canopy. The pick-up
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machine then drives down picking up the windrow of nuts and separating out any debris. The crop is elevated into a hopper on the harvest machine and off-loaded into trailers for transport to a bunker. The crop is stock-piled in the bunker until the harvest is complete and it can be trucked to the processor.
A pick-up harvester collects the windrowed crop (Jubilee Almonds).
The harvested crop is elevated to a bunker (Jubilee Almonds).
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Harvested crops are not safe to stockpile unless the moisture content is down to about 5%. At this stage the kernel will snap in half. At moisture levels higher than this the nuts will deteriorate due to mould and spontaneous combustion can occur. The stockpile is left uncovered unless temporary covers are needed for rain protection. Almond crops are bulky because of the amount of hull in the harvested crop. However, hulls are a marketable by-product and valued as a high-protein stock feed. Harvest is a dusty operation and when all is complete, the trees are irrigated. The different varieties of almond are usually kept separate because their end use is specific. The first variety to be harvested is Nonpareil followed by Peerless and Price, then Ne Plus Ultra, Carmel, Mission and Monterey and, lastly, Fritz. While yields vary considerably from cultivar to cultivar, there has been a steady increase in yield in recent years due to improve management techniques. Yields of four tonnes of kernel per hectare for mature orchards have been achieved with some varieties.
After harvest, almonds are trucked to the hulling plant for hulling and cracking. The bulk of the almond crop is marketed as kernel.
Post harvest The bulk of the almond crop is sold as kernel. While a few growers have their own hulling and cracking plant, most almond crops are transported to a central processor for hulling and shelling. There are large almond processing plants in the Riverland district in South Australia. Varieties that are marketed in shell are hulled and those marketed as kernel are hulled and cracked. After hulling, shear-roll machines crack the nuts and the shell is separated out and the kernel is then graded. Kernel sizes range from largest of 18 to the
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ounce down to 32 to the ounce. Kernel is trucked to a processing plant for further processing and packaging. Depending on demand, a percentage of product is valueadded by blanching to remove the membrane, or roasted and flavoured before packaging. Different varieties of in-shell almonds produce different kernel percentages. Crackout also varies with the season. As a guide, Nonpareil and Carmel head the list with a 65– 70% crack-out percentage followed by Price, Ne Plus Ultra and Fritz, then Mission and Peerless and lastly hard-shells at about 30–35% crack-out.
Kernel at the processing plant is conveyed for packing (Almondco).
Marketing Australian almonds are sold on the domestic market and an increasing percentage is exported. Most almond growers sell their crop to the larger processors who have established markets and product promotion. A small number of growers sell their product independently through local markets, wholesalers and retailers. The Almond Board of Australia expects that the annual crop will increase to 20 000 tonnes of kernel by 2008 as new extensive plantings come into production. This increased production is predicted to create an extra A$60m at the farm gate. Some almond product is imported into Australia but in the main this is a manufacturing grade product for use in baking and confectionery. The Australian industry produces high quality nuts and there is a growing export demand for quality Australian almond kernel. Prices received at the farm gate vary considerably according to variety and nut quality and competition in world almond markets is affected by government subsidies in the
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different producing countries. Currently Australian growers receive up to A$6.50/kg kernel. While the increased production worldwide is likely to affect future pricing, demand is also increasing due to greater promotion of the health benefits of nuts.
Further reading Almond Board of Australia website http://www.aussiealmonds.com.au Australian Nut Industry Council website http://www.nutindustry.org.au Bennett, C. (2001). Almond varieties in Australia. Australian Nutgrower 15(1), 9. Bennett, C. (2002). Good root system with drip irrigation. Australian Nutgrower 16(3), 12. Bennett, C. (2004). Almond management trial challenges current production knowledge. Australian Nutgrower 18(3), 22–23. Bennett, C. (2004). Almond nutrition – forget the recipes. Australian Nutgrower 18(4), 8. Gathercole, F. J. ‘An introduction to Commercial Almond Growing in Australia.’ (SARDI Loxton Centre for Australian Almond Growers Association: Loxton, South Australia.) Horticulture Australia website http://www.horticulture.com.au/project Jackson, J. F. (2004). Cross pollination is essential in almond orchards. Australian Nutgrower 18(2), 3–5. McMichael, P., and Pettigrew, S. (2004). Bacterial Spot on almond. Australian Nutgrower 18(2), 24–28. Micke W. C. (Ed) (1996). ‘Almond Production Manual’. (University of California publication 3364: California, USA.) Ohlendorf, B. L. P., and Strand L. L (2002). ‘Integrated Pest Management for Almonds’. (University of California, publication 3308: California, USA.) Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Sedgley, M., and Granger, A. (2000). Pollination of almond. Australian Nutgrower 14(3), 7. Wirthensohn, M. (2002). Breeding for quality in almonds. In ‘Proceedings of the 2002 Australian Nut Industry Council Conference’. p. 56. (Australian Macadamia Society: Lismore, NSW.)
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10 Cashews
Background The cashew or Monkey Nut is native to tropical America and north-eastern Brazil in particular. Cashew trees thrive in warm humid climates where there is an annual rainfall greater than 1000 mm and they grow from sea level to an altitude of 1000 m. Cashew is cultivated primarily in India, Brazil, Vietnam, Tanzania and Mozambique. Plantings have also been established in west Africa and Australia. Cashew trees are robust fast-growing evergreen trees that tolerate periods of drought. The nut that forms at the base of the cashew apple is highly valued as a roasted snack nut, in confectionery, and in cooking, but the apple also has value. Cashew apple juice is a popular drink in many communities and it can be fermented into a Madeira-like wine. The fruit pulp can be made into preserves, jelly, candied fruit and syrup. However, the cashew apple harvested from commercial plantations is discarded when the nut is removed due to lack of markets for apple products. It has been reported that in India alone approximately 1.25 million tonnes of cashew apple is wasted each year. The liquid enclosed in the shell is called cashew nut shell liquid (CNSL) and it is caustic. It contains cardol and anacardic acid and acts as a vesicant producing burn-like blisters when in contact with human skin. However, CNSL has many industrial uses because of its polymerising and friction-reducing properties. It also has a use as a waterproofing agent and preservative. When distilled and polymerised, the oil is used in varnishes, cements, tiles, lubricants and inks. It has also been used in tropical medicine. Commercial cashew production in Australia is in its infancy and Cashews Australia is the only commercial plantation at this stage. Planting began in 1989 on the Cashews Australia property near Dimbulah in north Queensland and tree numbers now total approximately 45 000. A second commercial planting is being established at Wildman River in the Northern Territory. Trial plots were first planted in the 1960s and 1970s by private and government interests in Queensland, Northern Territory and Western
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Australia. Two small plantings for varietal collection were established near Katherine during the 1990s and have not been developed further. A trial planting at Kunanurra in the Ord River Irrigation Area of Western Australia was abandoned due to low yields. The Cashews Australia plantation has been the pioneer plantation in Australia and has instigated research projects to improve commercial varieties and cultivation management. While there has been interest shown by a few investors in expanding cashew production in Australia, cultivar improvement is required to improve yield. However, the major limiting factor has been the difficulty of processing cashew product and the lack of a nut processing facility. Nonetheless, cashew production in Australia totalled 300 tonnes of nut-in-shell in 2004 and this is expected to steadily increase as new plantings come into bearing (Shearer, Shearer, personal communication). At present, most cashew product is transported to India, Vietnam and China for processing. The capital cost of establishing a viable cashew orchard is substantial. However, the minimum size of a viable cashew plantation would depend on the machinery required and on the processing and marketing facilities available. It has been suggested that a plantation of 200 ha is required to achieve sufficient nut volume to negotiate with overseas processors.
Botany Cashew (Anacardium occidentale) belongs to the Anacardiaceae family. Pistachio and mango also belong to this family and the cashew tree foliage is very similar to pistachio foliage. Cashew trees are evergreen and grow rapidly to form a large much-branched tree of some 15 m in height. The leaves are ovate and leathery and the inflorescence is polygamous having male, female and hermaphrodite flowers.
Cashew panicle with flowers (P. O’Farrell).
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Specific requirements Soil Cashew trees grow best on a deep well-drained soil and the preferred soil type is sand or sandy loam. They also grow on light clay soils where drainage is adequate. The required soil pH for cashew trees is slightly acid to neutral ranging between 5.5 and 7.0.
Climate Cashews grow best in tropical regions where there is a distinct wet and dry season and no frost. The climatic zone suggested in Australia is located north of 17°S latitude. Monthly mean temperatures during the day should be no less than 10°C. Cashews tolerate temperatures above 40°C. For successful nut production, the weather should be dry from flowering and nut set to harvest, a period that may last six months. Cashew trees can be damaged by wind and areas prone to cyclones should be avoided. Trees may require the protection of wind breaks on windy sites. Rain and water requirements. While cashew trees grow well in tropical regions without irrigation, for commercial nut production irrigation is required during the dry season and also during dry spells in the wet season. It has been suggested that the irrigation water requirement for cashew trees is 3.5 Ml ha–1 but this would vary according to age of tree, season and location.
Location Topography. Because cashews grow in areas of high rainfall, sloping land should be avoided to reduce the risk of soil erosion. Level land is also preferred for irrigation efficiency and it is beneficial for machinery operations in the orchard, particularly harvesting. Rocky sites are not suitable because the rocks damage machinery. Facilities. Because cashew processing is complex and expensive it is sensible for economic reasons that orchards are located close to a central processing facility. Close proximity to shipping facilities also provides greatest efficiency for the cashew product that is to be exported for processing. However, dried cashew product is robust and can be transported over long distances.
Flowering and pollination The flowering time of cashew trees extends over a few months and while in some locations flowering occurs in the mid dry season, flowering may extend beyond that in other locations. Each tree produces a profusion of flowers and they include three different types of flowers: staminate, pistillate and hermaphrodite flowers. Cashew is pollinated by insects, primarily ants and native bees, but in India it is reported that artificial pollination is required. Most flowers fall off prematurely but many remain to form fruit. The flowers are small, pinkish in colour, and narrowly trumpet-shaped with five small petals. They form in large panicles. After fertilisation, a purplish-coloured kidney-shaped fruit forms at the base of a green stalk and as it matures, this stalk-like
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structure, known as the cashew apple, swells to form a fleshy fruit. The cashew apple varies in size and weight ranging from less than 100 grams to over 500 grams. The cashew apple has a thin skin, is easily bruised, and as it matures the colour turns yellow (or red) and becomes fragrant.
Panicle with developing cashew nuts (P. O’Farrell).
Cashew panicle with mature fruit (P. O’Farrell).
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The cashew fruit at the base of the apple is enclosed in a dark brown skin covering the hard shell that contains the cashew kernel. The CSNL is contained within the mesocarp, an area between the outside and inside surfaces of the shell. When fully mature, the cashew nut and its cashew apple stalk fall to the ground. The time from fertilisation to fruit maturity can vary from two to three months depending on the variety, tree health and the daily temperatures during fruit growth.
Orchard layout Tree spacings vary mostly due to variety and amount of available land. Spacings of six metres between trees and rows eight metres apart have proved successful while 12 metre spacings have also been tried. Greater tree density may be appropriate where hedging of mature trees is intended.
Cashew cultivars Cultivar improvement programs have been, and will be, essential to the success of cashew production. Seedling trees are highly variable and research has identified selections and hybrids that are high-yielding, produce good quality nuts and are suited to Australian conditions. However, at this stage while private assessments are continuing, research by Government agencies has ceased. Preferred characteristics for commercial production include: site suitability; upright trees with good branching habit and a large number of terminal shoots; large nut size; kernel recovery of more than 30% and a minimum yield of 3.8 tonne per hectare. Cultivars reported to have potential include KAM 2, KAM 6, Guntur, 9/14, and TN 10203, 12310, 20216 and 21406.
Cashew rootstocks Rootstocks are raised as seedlings and the most vigorous specimens are selected.
Propagation Cashew trees can be grown by direct in-field seeding of germinated seed. Work to improve nursery propagation techniques has been conducted in Western Australia where the rootstock seed is cleaned of surface fungi and dirt before sowing, convex side uppermost, in pots or bags of sterile potting mix. Germination takes a couple of weeks in warm weather but can take over a month in cool weather. The seedlings grow rapidly and are ready for grafting within two months. Seedlings with straight stems are preferred. Wood for grafting of similar diameter to the rootstock is selected from selected mother trees. Leaves are removed to promote bud swell before the scion wood is pruned off the mother tree. The rootstock seedling is pruned back to about 10 cm from the base for grafting. Wedge grafting is the recommended method of grafting. A vertical cut is made in the rootstock and the wedge shaped base of the scion wood is inserted. The graft union
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is bound with grafting tape and covered with a plastic bag. Including leaves growing on the rootstock in the bag increases humidity and graft success rate. The grafted trees are kept in the shade and the bag is removed when the new leaves grow. The grafting tape is removed after about a month and the trees will be ready for planting in 3–4 months. The trees are placed in the sun to harden before planting out in the orchard. More recent methods of grafting have been adapted from Vietnam and these methods may produce a higher success rate.
Planting techniques Trees are usually planted in the dry season and spring during warm weather. Planting in cool weather can slow root development. Before planting, the soil is watered and the cashew trees are removed from the container taking care not to disturb the root system. The trees are planted into the planting hole and watered immediately after planting. Keeping the soil moist until the trees are established is essential.
Management of young trees Adequate soil moisture is important for growth of young cashew trees. Micro-sprinklers have proved to be more suitable than drip systems in most locations. To promote optimum growth, young trees are fertilised frequently with a fertiliser containing nitrogen, phosphorus and potassium. Other elements such as zinc may also be required in some soils. The nutrient status of the tree should be obtained via soil tests and leaf analysis. Weeds grow rapidly in the moist fertile conditions and regular weed control is required. Care must be taken not to contact the leaves of the tree with systemic herbicide. Mulching around the trees is beneficial. Tree training involves removing all growth below the graft. Some young cashew trees have been trained to a vase-shape but in the main, they are left to grow apart from the removal of lower branches to allow machinery access under the trees. To ensure machinery access, maintaining a clear trunk of one metre before branching is recommended.
Management of bearing trees With good management the time from planting to nut production can be as little as two years. Cashew trees do not require large amounts of water but irrigation during dry periods enhances nut yield and quality. Soil moisture monitoring devices can be used and water quality should be checked to ensure a salinity level of less than 0.8 dSm m–1. High iron levels in the water can cause blockages when drip irrigation emitters are used. Research has shown that the application of nitrogen can promote vegetative and floral development of cashew and that the timing of the application influences the timing of nut drop. Because it is important to harvest nuts in dry weather, working for a preDecember nut drop is desirable. This can be achieved to a certain extent by applying nitrogen during the growth phase (December to April in some regions). This results in pre-July vegetative and panicle development and a greater proportion of pre-December
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nut drop. Fertilisers can be applied via a fertigation system and trace elements are applied as a foliar spray when required. A pre-harvest clean-up of the orchard floor is necessary before harvest. This includes removal of low branches that would obstruct harvest machinery, and picking up fallen branches, old carry-over crop, and mowing. Tree training of mature trees is generally confined to removal of low and broken branches.
Pests and diseases Cashew trees have not been troubled severely by diseases in Australia but they are susceptible to a few pests. Most of these pests also occur in mangoes.
Pests Caterpillars. Caterpillars can feed on leaves and flowers but this is mainly a wet season event and damage has not been reported as severe. Mango-shoot Caterpillar (Penicillaria jocosatrix) feeds on young leaves mainly during the wet season. Flower Thrips (Frankliniella sp.). Thrips can damage the developing fruit and nut. Damage can be severe and control may be required. Fruit-spotting Bugs (Amblypelta sp.). These bugs may suck sap from young fruit causing fruit drop, and from young shoots causing the shoots to wilt and die. Control may be required. Leaf Roller (Anigraea ochrobasis). Feeds on young leaves mainly in the wet season. Mosquito Bug (Helopeltis sp.). This insect pest may cause serious crop loss. Research work has shown that the green ant is an important biological control against this and some other pests. Pink-wax Scale (Ceroplastes rubens). This scale insect sucks sap in leaves causing defoliation. Red-banded Thrips (Selenothrips rubrocinctus). These insects feed on leaves causing defoliation. Termites (Mastotermes darwiniensis). Giant termites can be devastating in sandy soils in Western Australia and the Northern Territory where they have been reported to cause death of trees. Termite damage has not been reported in Queensland cashew (Shearer, personal communication). Vermin. Pigs and bats have been reported to eat cashew crop but the most troublesome pest is the rat that can cause fruit loss during the fruiting period and damage to irrigation equipment.
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Diseases Anthracnose. weather.
This disease can be troublesome in wet areas or during periods of wet
Leaf Spot (Pseudocercospora anacardii). (Also called Cercospora Blotch.) This disease causes leaf spots and in severe cases trees may defoliate.
Harvesting Some cashew selections may begin producing nuts within 18 months of planting out. While time to nut production depends on location and growing conditions, under favourable conditions trees planted in an orchard at 8 m × 6 m spacing have been reported to reach full production in 5–6 years. Yields vary significantly according to variety, location and management. A yield target of 2.8 tonnes of raw nuts per hectare with a kernel recovery of 30% is suggested as a figure to produce satisfactory returns. This is equivalent to 14 kg of nut-in-shell per tree when planted at a density of 200 trees to the hectare. Dry weather is essential prior to and during harvest. As mentioned above, fertiliser applications can be adjusted to ensure fruit drop finishes before the arrival of the wet season. In dry weather during nut drop, the apple remains firmly attached to the nut at harvest but if rain occurs during nut drop, the apple may rot on the ground prior to harvest. The orchard floor is cleaned prior to nut drop. Traditionally cashew fruit is harvested by hand and the crop can lie on the ground to dry in fine weather but it must be harvested if the weather is wet. Cashews Australia is the only plantation in Australia to use mechanical harvesting equipment (Shearer, personal communication). Equipment similar to almond harvesting equipment is used to sweep the fallen product into windrows and a pick-up machine collects the product into bins. The harvest process is repeated over about three months until fruit drop ceases. The cashew nut remains firmly attached to the cashew apple and consequently the bulk of harvested product consists of cashew apple.
Post harvest After harvest the cashew product is transported to a cleaning belt for removal of debris and it is then conveyed into driers. Ambient air is used in the drying process and drying can take a few days. The dried product is then stored in a dry atmosphere protected from vermin, usually in silos, until it is processed to remove the nut from the cashew apple. The dried product will remain in good condition for a year under good conditions. Removing the nut from the cashew apple requires specialised machinery and a facility to do this has been developed at the Cashews Australia. As mentioned above, a caustic liquid known as CNSL is contained in the shell. This liquid is pale yellow to brown in colour and it can cause severe dermatitis and blisters to workers if it contacts the skin. Unfortunately there is no machine available at present to
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separate the kernel from the testa and shell. Therefore, all Australian product is sent overseas for hand shelling. Overseas processors are interested in volumes of 100 tonnes or more of raw nut.
Marketing Because of the current need to process cashews overseas, it is likely that growers would choose to join together for processing and marketing purposes. The Australian crop in 2004 totalled 300 tonnes of nut-in-shell. World prices for top quality kernel during the years 1999 and 2000, varied between US$4.15 and US$3.25 per pound (A$12.00 and A$9.40 kg). Prices received for Australian produce have not changed significantly in recent years and the price received is dependent on the recovery rate of the kernel and the currency exchange rates. A north Queensland farm gate price of A$1.63/kg nut inshell is considered average for product with a 30% recovery rate. This price is based on a wholesale price of A$7000 per tonne for kernel, less transport and overseas processing costs. While cashew nuts are high value nuts, large volumes of imported product is available at relatively cheap prices.
Further reading Australian New Crops website http://www.newcrops.uq.edu.au Blaikie, S., O’Farrell, P., Müller, W., Wei, X., Scott, N., Sykes, S., and Chacko, E. (2002). Assessment and selection of new cashew hybrids. Publication No. 01/177. (Rural Industries Research and Development Corporation: Canberra, Australia.) Cruz, F. S., and Fletcher, R. J. (1996). Identification of superior cashew trees for northern Australian conditions. In ‘Proceedings of the First Australian New Crops Conference, Gatton College: University of Queensland’. (Eds B. Imrie, I. Wood, B. Bray and R. Fletcher.) (Rural Industries Research and Development Corporation: Kingston, ACT.) Grundon, N. J. (2000). The Australian cashew industry: an information system. Publication No. 00/15. (Rural Industries Research and Development Corporation: Canberra, Australia.) Grundon, N. (2003). ‘Growing Cashews – before you start.’ (Queensland Department of Primary Industries and Fisheries: Brisbane.) Grundon, N., O’Farrell, P., Hinton, A., Kulkarni, V., Leonardi, J., Blaikie, S., Richards, N., Armour, J., Shearer, P., Duncan, I., and Hood, S. (1999). ‘Cashew Information Kit.’ (Department of Primary Industries: Brisbane.) Grundon, N. (1999). Growing Cashews – common questions. Project no. 5343. (Queensland Department of Primary Industries and Fisheries: Brisbane.) Hinton, A. W. (1998). ‘Cashew production in North Queensland – estimating profitability.’ Research project. (Department of Primary Industries: Brisbane.) Hyde, K. (Ed) (2000). Cashews Australia. In ‘Thirty Australian champions, shaping the future for rural Australia’. Publication No. 00/141, Project No. UCA 4A. (Rural Industries Research and Development Corporation: Canberra.)
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Kirkpatrick, J. (1996). Cashews – A new industry full of promise. Good Fruit and Vegetables 7, 11–14. O’Farrell, P., Armour, J., and Reid, D. (2002). The effect of nitrogen on cashew in north Queensland 1995–99. Web Publication No. W02/001. Website http://www.rirdc.gov. au/reports/NPP/w02-001.pdf (Rural Industries Research and Development Corporation: Canberra.) Peng, R. K., Christian, K., and Gibb, K. (2000). Implementing ant technology in commercial cashew plantations and continuation of transplanted green ant colony monitoring. Web Publication No. W04/088. Website http://www.rirdc.gov.au/reports/ NPP/w02-001.sum.html (Rural Industries Research and Development Corporation: Canberra.) Robinson, D. (1995). ‘Establishment of cashews.’ Farm note 7/95. (Department of Agriculture: Western Australia.) Robinson, D. (1995). ‘Propagation of cashews.’ Farm note 8/95 (Department of Agriculture: Western Australia.) Rural Industries Research and Development Corporation (1998). Sub-program 2.3, cashews. In ‘Report of completed projects in 1997–1998 and research in progress as at June 1998’. (Rural Industries Research and Development Corporation: Canberra.) Rural Industries Research and Development Corporation (2004). ‘The New Industries Handbook.’ (Rural Industries Research and Development Corporation: Canberra.) Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Sivakumar, A. (2002). Cashew in the international edible nut trade. In ‘Nucis Newsletter. Information Bulletin of the Research Network on Nuts’. (Food and Agriculture Organisation of United Nations, Centre international de Hautes Etudes Agronomiques Méditerranéennes: Reus, Spain.) Wickens, G. E. (1995). ‘Edible nuts.’ Non-Wood Forest Products 5 (Food and Agriculture Organisation of the United Nations: Rome.)
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11 Chestnuts
Background The chestnut genus includes thirteen species ranging from low shrubs to tall trees. The native habitat of chestnuts extends through woodlands of southern Europe, Asia, North America and northern Africa. Three species of chestnut are grown commercially throughout the world, but in Australia the species grown for the sweet nut is Castanea sativa. This chestnut is commonly known as Sweet chestnut, Spanish chestnut or European chestnut. It is native to southern Europe from Italy to Iran and north to Hungary. Sweet chestnut is also found in North Africa. Chinese chestnut, C. mollissima, from northern China and the Japanese chestnut, C. crenata, are also grown commercially in some countries for nuts and timber. Sweet chestnut is thought to have been first brought to Australia in gold rush times during the 1850s. Chestnut production is concentrated in north-east Victoria and currently 70–75% of the national crop is produced in this region. Chestnuts are also grown east of Melbourne, in central Victoria, around Orange and Batlow in New South Wales, the Adelaide Hills in South Australia and near Manjimup in south-western Western Australia. Chestnut growers in Australia total around 340 but a number of orchards are quite small. For cost-efficiency reasons, the average size of new chestnut orchards is increasing. The Chestnut Growers of Australia Ltd is the industry body that represents growers. This organisation arranges grower education activities, chestnut promotion, and administration of levy funds for research projects. Australia currently produces some 1200 tonnes of fresh chestnuts annually and the industry expects that production will increase substantially in the next few years. Traditionally chestnuts are a food most highly valued by Japanese, Chinese and Europeans. Currently domestic consumption in Australia matches production but small quantities of product are exported and the industry is working to develop new export markets.
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Botany The sweet chestnut (C. sativa) is a large deciduous tree with a dense rounded canopy of deep green serrated leaves. Chestnuts are monoecious producing separate male and female flowers on the same tree. Chestnuts are mainly wind pollinated and after fertilisation nuts form inside a spiny burr. During summer the burr swells to about the size of a tennis ball. At maturity in autumn, the burr yellows slightly and splits open. The nuts fall both free of the burr and enclosed in the burr. Most chestnut varieties produce more than one nut in each burr and as many as five. In France chestnuts that have more than 10% with multi-embryos are called ‘chataigne’, and nuts that have a single embryo are called ‘marron’. Marron are large, sweet, easy peeling nuts and are prized in Europe for use in sweet desserts. Unlike most nuts that are dried, chestnuts in Australia are marketed fresh like a fruit and stored under refrigeration. Each chestnut is enclosed in a tough brown skin that must be peeled off to extract the white starchy kernel. Covering the fleshy kernel beneath the skin is a brown membranous pellicle that can be removed during cooking.
Chestnuts form in a spiny burr.
Sweet chestnut trees (C. sativa) grow to some 30 metres tall and can live for centuries in favourable conditions. The species is not resistant to chestnut blight (Cryphonectria parasitica). Fortunately this fungal disease is not present in Australia but it decimated chestnuts in North America in the early to mid 1900s. The American chestnut (C. dentata), was widespread in North America and an important timber species until annihilated by chestnut blight. American chestnut grows to a large tree and produces sweet but small nuts. The Chinese chestnut (C. mollissima) is a smallish tree and is the main species grown commercially in China where there are a multitude of named varieties. Chinese chestnut is the most blight resistant species and the nuts are easy to peel. While Chinese chestnut
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Chestnuts in burr.
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trees produce large nuts in subtropical areas, reports indicate that trees grown in temperate climates produce small nuts of variable flavour. This chestnut has been used to introduce easy peeling characteristics in chestnut breeding programs. The Japanese chestnut (C. crenata) is also a smallish tree growing to around 15 m and it produces high yields from an early age. It also shows a degree of blight resistance and produces the largest nuts of any chestnut species. However, nut size and quality is highly variable from cultivar to cultivar and the nuts are difficult to peel.
Specific requirements Soil Sweet chestnut trees grow well in a wide variety of soils providing drainage is good. While deep sandy loam is most favourable, some commercial plantings have been successful on less favourable soils when it is enriched with organic matter. Chestnuts tolerate reasonably acidic soils but the preferred pH range is between 5.5 and 6.5. Chestnuts do not tolerate alkaline soils.
Climate Temperature. Chestnuts grow best in warm temperate regions at an altitude between 100–800 m. The trees tolerate extremely cold climates but their chilling requirement is not as high as most other deciduous nut trees. However, growth may emerge too early where the winter is mild and may be damaged by spring frosts, and at the end of the season hot summer weather at nut fall can reduce nut quality. Water requirements. Traditionally most chestnut orchards on fertile valley soils are not irrigated. However, this has changed because the market demand is for larger sized nuts. The preferred annual rainfall is 750–1000 mm but irrigation is essential in dry seasons for good growth of young trees and to ensure good nut size. Humidity. Chestnut trees are susceptible to root-rot and nut-rot and both diseases are more severe in humid weather. Nut-rot in particular can cause crop loss when the weather is foggy or rainy during the growing season and nut fall. Shelter from wind. Chestnut trees tolerate some wind but nut production is enhanced where the orchard is sheltered from prevailing winds.
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Location Planting chestnuts in hilly country is manageable where nuts are harvested by hand. However, where nuts are to be harvested mechanically, orchards should be reasonably level to accommodate the large pick-up machines. The more level a site is the more efficient all tractor work is. The preferred location of a chestnut orchard is accessible to cool-storage, processing facilities and markets. To prevent problems with neighbours, due to machinery noise, bird deterrents and chemical use orchards are best located some distance from residential areas.
Flowering and pollination Chestnuts are pollinated by wind but pollen is also thought to transfer to the female flowers via insect activity. Flowering is quite complex because two types of catkins are produced. The first catkins in spring are monosexual catkins and they hang vertically from the new shoot and shed pollen first, then the bisexual catkins develop and these are much shorter and smaller than the monosexual catkins. The female flowers on the bisexual catkin are slightly spiky and form closest to the attachment point of the catkin. The male flowers are ball-shaped and release pollen from tiny pollen sacks. Most chestnut trees are self-sterile so more than one variety is required for cross-pollination and subsequent nut set. One special feature of chestnuts is that pollen influences the characteristic of the nut produced. Therefore, the pollinisors planted in an orchard are crucial to nut quality. This phenomenon is known as ‘xenia’.
The bisexual catkins are shorter than the monosexual catkins.
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Warm dry weather at flowering is essential for good nut set because rain and humidity impede pollen transfer and successful fertilisation. Wet weather also substantially increases the likelihood of nut-rot disease (Phomopsis castanea). In fine weather, pollen can travel some 60 m to another chestnut flower, but in an orchard situation cultivars are planted in alternating rows to maximise the chances of pollination. The female flower is not receptive to pollen until about five days after the flower is in full bloom but it remains receptive for almost two weeks. To ensure good nut yields and nut quality, it is important to select a polliniser variety that is compatible with the main crop variety and both should flower at the same time.
Orchard layout
Chestnut flowers.
Tree spacing in a chestnut orchard depends on location and management. When planted too close, the trees will soon become over crowded especially in fertile soils, and when planted too far apart there will be too much wasted space particularly in the early years. Many growers have found that planting trees on a seven-metre diamond grid suits well in northeast Victoria. Where the growing conditions are very favourable and vigorous cultivars are planted, tree spacing may need to be greater than seven metres, and in less favourable conditions where growth is not expected to be vigorous, tree spacing could be reduced. The orchard layout should be suitable for access of machinery down the tree rows and around the head of the rows. Optimum spacing also allows good light penetration and good air circulation in the orchard when trees are mature. Pruning management is important to tree spacing. In an intensively planted orchard, annual pruning will be essential to avoid overcrowding while in a widely spaced orchard, pruning may not be necessary, depending on the variety. When deciding upon tree spacing, it must be remembered that chestnuts grow into large trees and can live for many decades. Planting trees on the diagonal rather than the This block of chestnut trees has been top-worked to a more favourable cultivar. square allows for tree thinning to reduce
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crowding because every alternate tree can be removed without complete disruption of the orchard layout. In most situations it is not necessary to alternate single rows of the main cultivar with single rows of a pollinisor. Most growers have found that planting one row of the pollinating variety every four rows of main crop is sufficient for pollination.
Chestnut cultivars Years ago chestnut orchards were based on seedling trees but this is no longer the case and most seedling orchards have either been replanted or top-worked to improved cultivars. The most popular chestnut cultivars today are Buffalo Queen, Red Spanish, Purtons Pride and De Coppi Marone. These four cultivars mature in this order extending harvest from early season to late season and they currently form the basis of the Australian chestnut industry. Some other cultivars are grown or have been grown and are included in the following list.
Some chestnut cultivars April Gold. Mid-season variety; large attractive shiny nuts; compact tree. Bouche de Betizac. European/Japanese hybrid bred in France; early season; large attractive nut; dark in colour; good flavour and peeling; prone to nut-rot some seasons. Buffalo Queen. Slow-growing open tree; typical central leader shape; can be pruned hard; early season maturity and first nut on the market so commands good prices; large nut size particularly when trees are pruned; excellent yields; 50% of nuts fall free of the burr; not very susceptible to Phomopsis or Phytophthora. Chiuso Peiso. Imported Italian marone type; mid-late season; easy to peel and excellent flavour. Collosal. Imported hyrid from USA; early to mid season; large but dull nut. De Coppi Marone. Late season maturity; strong growing bell-shaped tree; sweet nut and very easy peeling; excellent keeping qualities and most resistant variety to Phomopsis; 50% of nuts fall free of the burr. Fleming’s Beauty. Early maturing; light-coloured medium to large nut. Fleming’s Reliance. Early maturing; reliable bearing; dark-coloured good quality nut; thin skin. Knox Early. Early season attractive nuts. Luciente. Precocious bearer; sets large crops of nuts but nut size is small if tree is not pruned; excellent flavour and easy peeling nut.
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Menzies. Favoured as a rootstock because it shows resistance to Phytophthora root-rot; good size nut but looks dull; is hard to peel and poor kernel quality. Purtons Pride. Also called Emerald Gem; excellent nut flavour and easy peeling; tends to set large crops so tree needs pruning to maintain large nut size; tends to grow vaseshaped. Red Spanish. Also called Wandenberg; shy bearer so no pruning is needed; very large nut; matures early in season after Buffalo Queen; reasonable drought tolerance. Sword. Out of favour as nut is difficult to peel and is therefore not suited to the fresh market; may be suitable for processing; large dark-coloured nut that falls mid season; vigorous growing tree. Wandiligong Wonder. Out of favour as it is susceptible to Phomopsis nut-rot; good peeling; late bearer so receives good price; shy bearer so no need to prune.
Chestnut rootstocks Rootstock for grafting is grown from seed. In the past any vigorous chestnut variety was used as rootstock. Since it has been found that Menzies cultivar shows resistance to Phytophthora root-rot, Menzies has been the favoured rootstock. Seed is collected at nut fall and buried in moist sand until it has germinated. As soon as possible after germination the seed is carefully planted in a nursery bed and grown on. When the trunk is a good pencil thickness it is ready for grafting. This may be after more than one year of growth.
Propagation Chestnuts are not difficult to propagate if the rootstock and the mother wood are in good health. The rootstock and cultivar to be grafted should be varieties of the same species. When the rootstock belongs to a different species to that of the cultivar, incompatibility and subsequent graft failure may occur. The most popular method of propagating chestnut trees is shield or ‘T’ budding that is done during spring when the risk of frost has passed and the rootstock seedlings have come into leaf. Dormant bud wood is collected during winter and stored in sealed wrapping under refrigeration until required. Budding using freshly collected green bud wood can be done in late summer. Other methods of chestnut propagation include whip and tongue graft when rootstock and scion are of a similar size, and cleft graft when the rootstock is large. Bark grafting is a successful method of top-working trees and it is done in spring or summer. (See Chapter 3 for a description of all propagation techniques.) Top-working has been widely practiced in chestnut orchards and many large orchards have changed from unfavourable varieties to favourable ones with great success. Growers have developed their own particular technique for top-working and the most popular one is to cut the trunk off at about shoulder height in the growing season and
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immediately insert several prepared scion sticks under the bark. The scion sticks are collected in winter and sealed and refrigerated until required. Another method used to top-work chestnut trees is to cut the main branches back and allow the new growth to grow to about thumb thickness. This new growth can then be grafted with new scion wood using whip and tongue grafts. Chestnut propagation from cuttings has been tried using both summer wood and dormant wood, however, reports indicate that success rates have not been encouraging.
Planting techniques Young chestnut trees are planted during winter dormancy into well-prepared soil. Deep ripping of the tree line is advised where a hard soil layer underlies the topsoil or where the soil is compacted. Treating trees before planting with a solution of beneficial fungi helps prevent root disease. Tree roots may also need to be treated with anti-gall solution where there is risk of Crown Gall. Chestnut trees are generally planted in winter as bare-rooted trees. The roots are trimmed, the tree is planted at the same level it was in the nursery and watered well. Fertiliser is not usually applied until new growth appears. In exposed sites sunburn may be a problem on young trees due to the lack of shade caste by the small canopy. In this situation it is wise to paint the trunk and main branches exposed to the sun with white plastic paint. Rabbit-proof guards may also be required.
Management of young trees Weed control is essential around young trees but care should be taken to avoid damage to trees through mowing operations or herbicide treatments. Nitrogen fertiliser is applied to newly planted trees when they come into leaf. To maintain soil moisture, regular irrigation is recommended for young trees in the growing season, particularly during dry periods. While many chestnut orchards survive without irrigation, irrigation in dry periods during the early years will promote growth and reduce the time between planting and the first crop. The aim in pruning young trees is to establish a strong branch framework. Winter pruning is done in dry weather to avoid disease problems. Chestnut trees are generally trained to the vase shape, pyramid or central leader, and a popular technique is the Japanese technique of opening out the branch frame to maximise light penetration. Different cultivars lend themselves to different techniques. In the early years, the aim is to prune trees to develop a well-spaced branch framework.
Management of bearing trees Irrigation While chestnuts are reasonably dry tolerant trees, water stress will reduce growth, nut size and yield. Irrigation is therefore beneficial and the frequency of irrigation will be determined largely by soil type, climate and planting density. While many orchards were
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not irrigated in the past, the trend today is for irrigation to ensure good nut size. Ensuring adequate soil moisture during nut development from mid summer to harvest is critical to nut size and quality. Drip irrigation systems are seldom installed in mature chestnut orchards because the root zone is large. However, drippers are adequate for young trees and where water is scarce, multiple drippers may be the most cost-effective method for irrigation of mature trees. Micro-sprinklers installed between trees is a popular option. Knowing when and how much to irrigate can be determined using soil moisture measuring devices. (See Chapters 5 and 6.)
Fertilising A combination of soil analysis and leaf analysis is the best guide to deciding what and how much nutrient to apply to growing and bearing trees. When determining nutrient demand for bearing trees, the replacement of nutrients removed from the orchard at harvest is also taken into account. Fertiliser application will, therefore, vary considerably from orchard to orchard depending on soil type, tree age, tree productivity and presence of nitrogen-fixing ground covers. The main elements applied during spring and summer are nitrogen and potassium. Phosphorus and other minor elements are applied as required to ensure optimum flowering and fruiting. Leaf analysis has revealed a boron deficiency in some orchards but zinc deficiency is the most common nutrient deficiency reported. The table below is a guide to the desirable range of nutrients in chestnut (leaf sampling time, mid summer). Element
Desirable level
Nitrogen
2.4–2.9%
Phosphorus
0.14–0.3%
Potassium
0.8–1.6%
Sulphur
0.15–0.25%
Calcium
0.6–1.4%
Magnesium
0.25–0.7%
Sodium
0–0.1%
Chloride
0–0.3%
Copper
4–20 mg/kg
Zinc
17–100 mg/kg
Manganese
50–700 mg/kg
Boron
33–90 mg/kg
Source of data: Weir and Cresswell (1993).
Pruning Traditionally chestnut trees were not pruned regularly but in recent years pruning has become an annual routine in an endeavour to increase nut size. Pruning in mature orchards also improves light interception. Chestnuts have a high light requirement for
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fruit production. Annual pruning to increase nut size reduces crop size and this reduces alternate bearing tendencies where an on-crop year is followed by an off-crop year. While pruning may reduce nut yields in the short-term, it is important to establish a strong tree framework while trees are young. Some chestnut varieties grow naturally as a central leader while other varieties have more spreading branches. The aim in pruning is to head back branches to promote fruiting wood and to remove crowded or broken branches. Tree training has changed over the years and the vase-shape popular in some orchards is now out of favour. The Pyramid or central leader continues to suit many chestnut varieties and the aim is to remove any branch that competes with the leader and remove any radiating lateral branch that is too close to another branch. The lateral branches should be approximately one-third the diameter of the central leader. The strongest lateral branches form a wide angle to the trunk and narrow angled branches should be removed before they split and damage the trunk. Because nuts fall to the ground and foliar spraying requirements are minimal, chestnut trees can be allowed to grow as tall as the row spacing permits without causing shading. The most popular pruning technique today is based on the Japanese method demonstrated by Dr Araki in Australia in 1998. The technique is not to force a particular shape on a tree but to open out branches to maximise light interception. This includes allowing low branching to develop to promote early fruiting. Dr Araki’s method should begin in the first year of growth and continue regularly throughout the life of the tree. The initial aim is to promote a leader and two main branches in a balanced configuration. In following years, inward-growing branches are thinned to encourage the tree to spread out. In time the central leader can be removed and side branches from the two main scaffold branches will fill the space. Annual maintenance pruning involves cutting back a third of the previous season’s growth. While the height of the tree is controlled, branch spread is maximised. The aim of this technique is to promote maximum nut size and yield. Another method of chestnut pruning, called canopy pruning involves pruning back the fruiting wood produced by the tree in the previous season. This method is timeconsuming and not practical if trees are large. Where older trees have become crowded, light interception is reduced and yield will decline. In this situation heavy pruning can rejuvenate trees and chestnuts in good health respond well when some of the main branches are completely removed. Where an orchard is very crowded it may be necessary to remove alternate trees as well as thin out the tree canopy.
Pests and diseases Chestnuts in Australia suffer few pests and diseases. While root-rot and nut-rot can be troublesome, no pesticides are routinely used in most chestnut orchards. Birds can reduce yields in some areas. Chestnut pests overseas include chestnut weevils, gall wasp, chestnut codling moth and chestnut moth.
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Pests Birds. Rosellas, galahs and cockatoos eat nuts, dropping many on the ground, and they can damage buds. Crop loss can range from severe to minimal depending on the region. Vermin. Rabbits can be troublesome to young trees and tree guards may be necessary. Similarly, wandering livestock and wallabies may damage young trees in certain areas.
Diseases Chestnut Blight (Cryphonectria parasitica). While Australia is free of chestnut blight, the disease is the most serious threat to the chestnut industry. This disease decimated both native and cultivated chestnut plantings in North America. Root and Crown Rot (Phytophthora cambivora and/or P. cinnamomi). Commonly known as ink disease in Europe or crown root canker in America, Phytophthora root-rot has caused numerous tree deaths in Australia. It is a soil-borne fungus that attacks the roots and the roots release a sap that turns black through oxidation of the tannins and the root system gradually dies. This causes pale listless foliage and gradual death of the branches. Dieback usually starts from the top of the tree and it is not uncommon for trees to take several years to die. The fungus becomes activated in spring when the soil temperature increases. While poor soil drainage favours development of the fungal disease, trees in well-drained soils may also succumb. Symptoms are particularly visible during dry years. There have been many treatments trialed for control of root and crown rot. These include trunk injection of phosphorous acid (PA), foliar spraying of phosphorous acid, application of appropriate fungicide granules on the soil, and fungicide foliar spray. While some growers believe that foliar sprays of phosphorous acid are effective in controlling the disease, this has not been confirmed through research. Another method of control to have been trialed is applying organic matter around the root zone to increase the range of micro-organisms in the soil. The preferred mulch to apply is a heavy layer of organic poultry manure and lucerne hay. Weeping wounds on the trunk can also be treated by cutting away the affected timber and painting with a Bordeaux paste of copper sulphate and lime. Different chestnut cultivars show varying susceptibility to the disease and in recent years, growers have been planting trees that are grafted on Menzies rootstock that has shown some resistance. Dipping young trees before planting in a solution containing micro-organisms that are antagonistic to Phytophthora can also be beneficial. Phomopsis (Phomopsis castanea). This fungal disease causes nut-rot and is detected after harvest. It can cause serious nut loss when rain falls during harvest but in dry seasons most varieties in most areas do not show signs of the disease. While a number of fungi have been identified in nuts with kernel rot, Phomopsis is the major disease of concern. Phomopsis infection of burrs may occur after flowering and cause premature nut drop. It is thought that the disease may be present in chestnuts showing no sign of nutrot at harvest and could develop in the nut during storage. Affected nuts have a
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distinctive smell that many growers have learnt to detect. When contamination is detected, appropriate measures can be put in place to remove affected nuts before sale. However, nut-rot is not visually obvious unless the nut is cut open to show the discoloured grey flesh. Sale of affected nuts on the fresh market is extremely damaging to the whole chestnut market. For this reason chestnut varieties that are prone to Phomopsis are now out of favour and varieties that show resistance to the disease are promoted. It has been found that the incidence of nut-rot is reduced in harvested chestnuts when the trees are sprayed with a fungicide during summer, but there is no recommendation for this treatment. The current strategy is one of prevention by growing varieties that are not prone to the disease, by harvesting fallen nuts as soon as possible, cooling the nuts to coolroom temperature as soon as possible, and keeping storage time to a minimum.
Harvesting Chestnuts are the only nut to be harvested by hand on a commercial scale and rubber or leather gloves are used to protect hands from the spines on the burrs. Nuts in the burrs can be removed by rolling the burr under a boot to split the burr open. Hand harvesting however, is gradually being phased out because pickers are scarce and the labour costs are high. The delay in changing to mechanical harvest has been due to the difficulty in designing a mechanical harvester that does not damage the surface of the nut. Because the bulk of the Australian chestnut crop is sold fresh, the visual appeal of an unblemished shiny nut is important. Many harvesters have been trialed. The main method has been to
Chestnuts must be harvested carefully to retain their glossy appearance.
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sweep the nuts into a windrow and use vacuum machines to suck up the nuts and burrs via long hoses. Apart from the risk of scratching the nut, gentle mechanical separation is then required to remove leaves, burrs and other debris. A newly designed harvester has shown promise and is currently being manufactured. This harvester uses a system of brushes to pick up the nuts and burrs and convey them to a bin. The crop is then put through a de-burring machine to remove the burrs. While the harvester shows no detectable damage to the nut surface, the de-burring machine must be operated carefully to minimise the risk of surface blemish. The chestnut industry must mechanise harvest operations to remain sustainable and therefore some slight loss of visual nut appeal may have to be tolerated. The use of mechanical harvesters introduces new requirements in the orchard. Access for machinery and a clean level surface on the orchard floor is necessary for efficient pick-up.
This chestnut harvester is fitted with front wheel brushes that sweep the nuts into the path of the central pick-up brushes. These brushes are designed to minimise damage to the nuts. After pick-up, the chestnuts, both in and out of the burr, are conveyed into a bin at the rear of the machine. This bin can be tipped into a de-burring machine which removes any debris and elevates the nuts in burrs to de-burring rollers (George Turnbull).
Tree shakers have not been used for chestnut harvest in Australia because nut maturity extends some weeks and shaking may cause immature nuts to fall. Nuts that fall prematurely in the burr are often shrivelled and burrs may be difficult to open. However, with improved tree shaking techniques, there could be a place for tree shakers particularly at the end of the harvest season. Nuts that fall within the burr are protected from ground moisture and possible development of Phomopsis nut-rot. If the weather at harvest is warm to hot, fallen nuts can overheat, lose moisture and quality deteriorates. Similarly, nuts that lie on damp ground may also deteriorate. The aim, therefore, must be to harvest the nuts as soon as they fall and cool them immediately.
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Yields vary according to the season, the orchard and the variety. However, a figure of over 10 kilograms per tree has been reported for eight-year-old trees.
Post harvest When the harvested nuts arrive at the grading shed, some growers place them straight into the cool-room while other growers process the nuts to remove sub-standard nuts and debris before placing them in the cool-room. Generally chestnuts are containerised in fruit bins at harvest but a bin full of chestnuts takes some time to cool thoroughly. For this reason, some growers ventilate the bin of nuts with slotted pipes to assist cooling. Other growers dip the bin of freshly harvested nuts into chilled water as a pre-cooler. Before market the cooled chestnuts are graded. The chestnut grading line consists of a trash remover to remove any leaf, burr or other debris, a water bath to remove the blank floating nuts, a fan to reduce surface moisture, and an inspection line to remove substandard nuts. At this point the nuts can be returned to the cool room or conveyed to a size grader. In some countries nuts are graded according to the number of nuts to a particular weight but in Australia nuts are size graded by falling through holes that range from 25 mm to 41+ mm diameter. The size grader is generally one or two large rotating drums and the nuts are slowly fed into one end of the drum and they roll down a spiral until they fall through a hole and into holding bin below. The size grades are: Small, Medium, Standard, L1, L2, L3 and L4. The nuts are then packed into 5 kg boxes or 10 kg bags. A weight margin is usually added to allow for possible moisture loss. The moisture content of freshly harvested chestnuts is around 50% and loss of moisture and, therefore, loss of weight, begins soon after harvest. To minimise moisture loss, the humidity of cool rooms is set greater than 90% and the temperature is maintained at 0°C. Stored nuts are monitored closely for the development of surface moulds. Incidence of mould growth is reduced where controlled atmosphere is available because reduced oxygen levels reduce mould growth. It is recommended that nuts stored for more than two months should be stored in plasticlined hessian or polythene bags under controlled atmosphere cool-room conditions. In most orchards the chestnut crop is transported to market in refrigerated transport as soon as possible after harvest.
Marketing The market for fresh chestnuts in Australia is largely limited to people of Asian and European origin. At present most growers sell the bulk of their crop through the fresh markets in each state, however, some growers sell direct to retailers. The price of fresh chestnuts on the local market fluctuates according to supply and demand but generally large sizes exceed A$4/kg while small sizes can be well below that. The chestnut industry is working to develop additional markets as this is essential to sustain increased production. Export markets are being established and small quantities of fresh chestnuts have been exported to Japan and Singapore. However, fresh nuts
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become very expensive for the overseas consumer because the orders have been small and air freighted. Export via shipping container is more cost-effective and the chestnut industry is hopeful that larger orders for fresh processed chestnuts will be estabished. Large-sized chestnuts are favoured for the fresh market and the demand for small nuts on the fresh market has declined. Much work has been done in Australia into different forms of chestnut processing. One of the problems has been the development of a suitable peeling machine. Another problem is that while freezing the processed product is the most acceptable form of storage from a visual point of view because the pale chestnut colour is retained, freezing is expensive. When preserved via heat sterilisation and vacuum packed, chestnut products become an unattractive brown colour. Processing for chestnut meal could provide new market opportunities for small size nuts. Other processed products are chestnut puree and frozen, ready-to-heat, roasted chestnuts. It should be noted that in Japan, Australian chestnuts are highly regarded for their good flavour and quality appeal.
Roasting chestnuts on a commercial scale (J. Casey).
Chestnut production is increasing in Australia and the current annual crop of 1200 tonnes will be exceeded as new trees come into bearing. Yields per hectare vary greatly with orchard management, locality and variety but five tonnes per hectare is reported to be achievable under favourable conditions.
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Further reading Ahrens, G. (2002). Chestnut grove response to Dr. Araki’s technique. Australian Nutgrower 16(2), 27. Australian Nut Industry Council website http://www.nutindustry.org.au Berg, G. (2003). Chestnut Blight – a potential threat. Australian Nutgrower 17(1), 27. Casey, J. (2002). Value adding Australian chestnuts. Australian Nutgrower 16(3), 27. Chestnut Growers of Australia Ltd website http://www.chestnutgrowers.com.au Horticulture Australia website http://www.horticulture.com.au/project New Zealand Chestnut Council (1997). ‘Chestnut Growers Handbook.’ (Waikato: New Zealand.) O’Kane, B. (2001). Chestnut varieties for domestic and export markets. Australian Nutgrower 15(1), 24. O’Kane, B. (2001). Top-working chestnut trees. Australian Nutgrower 15(2), 24. Paterson, I. (2003). Chestnut meal – extension of shelf life. Australian Nutgrower 17(4), 29. Ridley, D. (Ed) (1999). ‘The Australian Chestnut Growers Resource Manual.’ (Agriculture Victoria: Myrtleford, Victoria.) Rural Industries Research and Development Corporation website http://www.rirdc.gov.au/reports/index.htm Washington, B. (1996). Phomopsis nut-rot. Australian Nutgrower 10(1), 7–9. Weir R., and Cresswell, G. (1993). ‘Plant Nutrient Disorders: Temperate & Subtropical Fruit and Nut Crops’. (Inkata Press: Sydney.)
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12 Hazelnuts
Background Hazelnuts grown commercially in Australia are cultivars of the European hazelnut, Corylus avellana. This species is native to temperate regions of Europe including Turkey, Iran and Syria, where it grows as a shrubby tree. Generally, European hazelnut has a short husk with the nut protruding while many other species produce nuts in a closed husk. Other hazelnut species include: American hazel, C. americana; Turkish tree hazel, C. colurna (that includes two varieties: var. chinensis or Chinese tree hazel, and var. jacquemontii or India tree hazel); Beaked hazel, C. cornuta (with the variety californica or Californian beaked hazel); Himalayan hazel, C. ferox; Siberian hazel, C. heterophylla; Giant hazel, C. maxima; Japanese hazel, C. sieboldiana; and Tibetan hazel, C. tibetica. The common name for all species of Corylus in Australia is hazelnut while in America species of hazelnut are called ‘filbert’. In the United Kingdom the name ‘cobnut’ is generally used to refer to varieties of European hazelnut and name the ‘filbert’ is used to refer to the Giant hazel that has a long husk covering the nut. Apart from European hazelnut, the only other species of Corylus that produces a nut valued for human consumption is C. americana. The different hazelnut species cross readily and this has resulted in many hybrid forms. Hazelnuts have been grown in Australia since the early 1900s. Renewed interest in growing hazelnuts commercially emerged in the 1970s and 1980s and new orchards were planted. Unfortunately the trees planted in many of these orchards were unsuitable varieties or proved not to be true to type and yields were disappointing. Much research was conducted to rectify the problem. In recent years, new interest in growing hazelnuts has been generated following a thorough overhaul of nursery techniques, the establishment of identifiable cultivars and the importation of cultivars from overseas. Hazelnut cultivars purchased from reputable nurseries now provide reliable stock and today the annual yield expected from mature trees is in the order of five kilograms per tree.
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Hazelnut orchards are scattered throughout south-eastern Australia but the main hazelnut producing regions are the Central Tablelands of New South Wales, northeastern Victoria, and Tasmania. While the average size of hazelnut orchards remains relatively small and present annual production totals around 20 tonne, some large orchards have been planted in the last five years and production should increase substantially in the next few years. The trend to new plantings continues as do research trials funded by Rural Industry Research and Development Corporation. Research into hazelnut production is based at Orange in New South Wales. The Hazelnut Growers of Australia Ltd (HGA) is the national industry body and this association represents and supports growers and organises educational activities during the year. The HGA also works to maintain quality standards and coordinate with researchers on hazelnut projects.
Botany The hazelnut trees planted in commercial orchards (C. avellana cvs.) are smallish deciduous trees growing to around three metres tall. They produce suckers forming a thicket of foliage if left unpruned. Leaves are rounded with finely serrated margins. Hazelnut trees are monoecious with separate male and female flowers produced on the same tree. Hazelnut species are self-sterile: pollen produced by the catkins on one variety does not fertilise the female flowers of the same variety. The male flowers or catkins emerge in winter, often several to a bunch, and they gradually elongate and release pollen. The female flowers emerge in a cluster on bare branches and are tiny and deep red in colour and topped with two curved stigmas. The female flowers are wind pollinated during winter and early spring but pollination is a long complex process (see below). Following fertilisation, the female flowers develop into nuts enclosed in a leafy husk and after the end of summer the husks turn from green to brown, the leaves turn golden brown and nuts begin to fall. While the trees lose their leaves in winter, flowering during winter indicates that while the trees are deciduous, they are not completely dormant. Hazelnut catkins and female flowers emerge in winter.
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Specific requirements Soil While hazelnuts will grow on a wide range of soils, for commercial production the preferred soil is a sandy loam with a pH of 6–7. Although hazelnuts produce a deep tap root, feeder roots are relatively shallow. Trees will grow and crop on shallow soils but trees planted on deep soils will grow significantly larger and produce greater yields. Soils should be well-drained and contain a good amount of organic matter. Light sands and clay loams should be improved with the addition of organic mulch, and hard set soils or soils reduced in depth by a hard layer should be deep ripped in both directions prior to planting.
Climate Temperature. Hazelnut production is confined to temperate areas experiencing a mild to warm summer and cool winter. The trees are not troubled by frost despite the winter flowering. In fact, hazelnuts tolerate extreme cold including snow and winter frosts down to –15°C. While high summer temperatures are no problem, exposure to hot winds can be damaging to growth and the developing crop. Chilling requirements. Hazelnuts require more hours of chilling than most other types of nuts. The chilling hours required differs from variety to variety but generally a period of 1200 hours below 7°C is adequate. Rainfall and water requirements. In many countries hazelnut orchards are not irrigated but this is seldom the case in Australia even where the annual rainfall tops 900 mm. For commercial nut production irrigation ensures adequate soil moisture for good growth of young trees and high yields and quality nuts from mature trees.
Location Sloping land that is too steep for mechanical harvesting and other orchard machinery is not suitable for commercial nut growing. As with most nuts, birds can devastate nut crops before harvest and a site that is not plagued by cockatoos and parrots and crows will reduce the need for bird deterrents. While access to processing facilities and markets is desirable, orchards should be isolated from residential areas to prevent problems with neighbours due to machinery noise, bird deterrents and chemical use.
Flowering and pollination Hazelnut flowering time varies greatly with the climate and trees grown in mild regions may flower for months while trees in cold regions may flower for as little as a few weeks. Male catkins usually precede female flowers and peak flowering periods of male and female flowers may not overlap on the same cultivar. Thus, it is vital in commercial orchards to plant other cultivars or pollinisers to ensure catkins are produced at the time the female flowers on the main cultivar are receptive. These pollinisers must also be
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genetically compatible with the cultivar for pollination to be successful. The genetics of hazelnut fertilisation is very complex. Briefly it could be said that to be compatible, the allele (an alternative form of a specified gene) of the pollen must be different from the allele of the flower it is pollinating. Therefore, different pollinisers are compatible with different main crop cultivars. When the catkin extends, pollen is shed and carried by wind to the female flower. The pollen grain of a compatible variety grows to the base of the style on the female flower within 4–7 days of pollination but development is then suspended and remains quiescent for 5–6 months. By early summer, the shell (or ovary) enlarges and a green husk forms around it. When the shell is about half its eventual size, the ovule develops inside and fertilisation can take place. If fertilisation is successful, the kernel develops inside the shell and a nut is formed. By early to mid autumn, the husk yellows and dries and the nut falls to the ground in or out of the husk. Nut drop in commercial orchards extends up to six weeks depending on the weather conditions. For successful nut production, cross-pollination is essential. It is wise to plant a number of different pollinisers to ensure fertilisation because the weather at flowering can alter the flowering times of the different cultivars. Unfavourable weather such as strong wind or persistent rain at flowering can reduce the chances of fertilisation but severe Hazelnut sprig with fruit. frost is not damaging and hazelnut flowers tolerate extreme cold.
Orchard layout For successful nut production the selection of pollinisers and the placement of pollinisers are critical. Tree spacing and direction of rows should take into account the direction of prevailing winds, sunlight interception, drainage and intended method of harvest. As nuts from different hazelnut varieties are kept separate at harvest, the main crop varieties should be planted with this in mind. Suggested systems include planting a polliniser at every sixth position in every third row, or planting entire rows of different polliniser varieties between a 3–5 row block of main crop variety. Because the number of pollinisers takes up valuable space that could be used for main crop variety, using quality pollinisers is recommended. In America, one polliniser to seventeen main crop trees can achieve successful pollination but in Australia the usual number of pollinisers planted is greater than this. Planting a few main crop varieties that can also act as pollinisers is efficient use of orchard space and improved yields per hectare are possible. However, some hazelnut
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cultivars are planted purely as pollinisers. Despite the fact that the nuts on these pollinisers may not be worth harvesting, the trees shed large amounts of pollen late in the season and extend the pollination window of the main crop varieties. Some growers recommend planting 20% pollinisers and as many compatible varieties as possible are included to maximise the pollination window. Orchard rows are planted in a north – south direction where possible to optimise sunlight. Tree spacing is an individual decision based on site, climate and management. Trees planted on a 4.5 metre grid equate to 493 trees per hectare while trees planted on a 6 m grid equate to 277 trees per hectare. Many growers find a 5.5 m grid is adequate for machinery access down the rows and allows for tree growth. However, while the trees are young, this spacing results in vacant orchard space. Double density planting is initially expensive but it is popular in some regions because it makes better use of the area throughout the life of the orchard. In double density plantings, trees are planted approximately 3.5–4 m apart and alternate trees down the row are removed when they start to become crowded after 10–12 years. Tree rows are usually about 5.5–6 m apart. Example of a high density planting layout: B
b
C
b
B
h
B
b
C
b
B
h
b
B
b
B
b
B
b
B
b
B
b
B
B
b
B
b
B
b
B
b
B
b
B
b
b
B
b
B
b
B
b
B
b
B
b
B
B
b
H
b
B
c
B
b
H
b
B
c
b
B
b
B
b
B
b
B
b
B
b
B
B
b
B
b
B
b
B
b
B
b
B
b
b
B
b
B
b
B
b
B
b
B
b
B
B, Permanent Barcelona b, Temporary Barcelona C, Casina c, Temporary Casina H, Hall’s Giant h, Temporary Hall’s Giant
In this example, the trees marked in lower case are to be removed 10–15 years after planting. The planting includes a polliniser ratio of one polliniser (Casina and Hall’s Giant) to 11 of the main crop (Barcelona). If rows are six metres apart and trees are three metres down the row at planting, after tree thinning the maximum distance for a main crop variety from a polliniser is approximately 10 metres.
Hazelnut cultivars Hazelnut trees begin to bear nuts from year three and at year six trees should be producing around 2.0–2.5 kg of dried nut-in-shell. Production from mature trees varies according to variety, location, and management but is likely to be in the range of 2.5–3.5 tonnes to the hectare.
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Correct identification and reliability of the stock source of both main crop cultivars and pollinisers is essential to be sure of successful yields. Occasionally in the past, problems have arisen with some hazelnut cultivars that were not true to type, however, this problem will not occur if all new stock is purchased from a reputable nursery. To ensure reliability, all cultivars are propagated vegetatively from reliable mother stock. In selecting main crop cultivars there are many factors to consider. Different cultivars produce nuts that are suited for different markets. Some cultivars produce large nuts for the in-shell market while other cultivars produce small nuts for kernel and confectionary. Other factors to consider include genetic compatibility, and climatic suitability particularly regarding chilling hours. The shell of different hazelnut cultivars varies in size, colour and shape, and kernel also varies in size, shape, in the thickness of the pellicle (skin covering the kernel) and the ease of removing the pellicle.
Some hazelnut cultivars Atlas. An Australian selection; vigorous spreading tree with large round nuts suitable for in-shell market; fibrous pellicle; thin shell; early flowering. Barcelona (Oregon). A selection from USA forming an upright vigorous tree; round nut suitable for the in-shell market; fibrous pellicle; mid-season flowering. This cultivar is also called Fertile de Coutard, Aveline de Provence or Castanyera. Pollinisers suggested include: Casina, Butler, Jemtegaard #5 and Hall’s Giant. Butler. A selection from USA for in-shell market; forming an upright tree; oblong nut; non-fibrous pellicle; mid season flowering. Pollinisers suggested include: Barcelona, Ennis, Casina, Willamette, Lewis, Hall’s Giant. Casina. Spanish selection; moderate vigour; small nut for unblanched kernel market or confectionery; mid to late flowering. Pollinisers suggested include: Hall’s Giant, Butler, Ennis, Willamette, Lewis, Jemtegaard #5. Daviana. A selection from England; upright tree with few suckers; medium size oblong nuts; attractive round kernel with easy to remove pellicle; mid-season pollen shed; late female bloom; a polliniser for Barcelona, Butler, Tonda, Romana. Ennis. A popular selection from USA; erect vigorous tree; high yielding; large round nut; thin shell; excellent for inshell market; non-fibrous pellicle; mid season pollen shed; late female bloom. Pollinisers suggested include: Willamette, Butler, Hall’s Giant, Casina, Lewis, Jemtegaard #5. Hall’s Giant. German selection often grown as pure polliniser; sheds large amount of pollen late in the season; upright tree with few suckers; low yielding but large round nut for in-shell market; also called Merveille de Bollwiller and Geant de Halle. Gunslebert. Medium oblong nut with thin shell and strong flavour; fibrous pellicle that is difficult to remove.
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Jemtegaard #5 (J5). Grown as pure polliniser shedding large amounts of pollen late in the season; pollinates Barcelona, Ennis, Casina and Hall’s Giant; low yielding but produces large round nut for in-shell market. Kentish Cob. English selection; large oblong nut with flattish sides; large sweet kernel with deep groove; pellicle difficult to remove; also called Du Chilly, Longue d’Espagne or Webbs Prise. Lewis. Selection from USA; small round nut suited to kernel market; high-yielding; pellicle slightly difficult to remove; pollinates Ennis, Casina, Butler, Willamette, Hall’s Giant. Negret. Spanish selection; small erect tree; small nut; good kernel for blanching and confectionery; early season flowering; polliniser suggested: Tonda di Giffoni. Red Avelline. Spreading bushy tree; small oblong nuts similar to White Avelline but with chestnut brown shell; pellicle is deep red; early season flowering; nuts remain in husk. Segorbe. French selection; upright tree; medium to large nut; good blanching and use in confectionery; early season pollen shed; mid season female bloom. Tokolyi Cosford. Australian selection; vigorous grower; medium size round nut with fibrous pellicle; kernel blanches well and late flowering; also called Brownfield Cosford. Tonda di Giffoni. An Italian selection; smallish nut but good kernel for blanching and confectionery; pollinisers suggested include: Willamette, Oregon Barcelona and Hall’s Giant. Tonda Romana. An Italian selection; upright spreading tree; smallish nuts but quality kernel for unblanched markets; mid to late season pollen shed and mid-season female bloom; pollinisers suggested include: Segorbe and Barcelona. Tonollo. Australian selection; vigorous grower; medium size round nut with fibrous pellicle; kernel blanches well; early pollen shed; mid-season female bloom. Victoria. Australian selection; grows few suckers; high yielding; medium size flat-sided nuts; early season pollen shed and mid-season female bloom. Wanliss Pride. Australian selection; spreading tree; high yielding; large plump nuts suited to in-shell market; early flowering; performs well in mild winter climates; sometimes known as Wanlis Pride and Wandils Pride. White Avelline. Australian selection; spreading bushy tree, with small long sweetflavoured nuts that remain in the husk; early flowering.
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Willamette. Selection from USA with moderate vigour; smallish round nuts; good blanching; suited for in-shell or kernel markets; early flowering; pollinisers suggested include: Tonda di Giffoni, Casina, Hall’s Giant, Butler, Ennis, Lewis. Woodnut. Australian selection; grows with few suckers; high yielding; medium size conical good flavoured nuts; late pollen shed; mid-season female bloom.
Hazelnut rootstocks The hazelnut industry in Australia is based on trees propagated in stool beds and by layering. Very few cultivars are grafted onto rootstocks. However, grafting trees onto nonsuckering rootstock would eliminate the need to continually remove sucker growth from around the base of the tree. The species developed as a non-suckering rootstock is the Turkish tree hazelnut (C. colurna), however, this rootstock tends to over-grow all but the most vigorous cultivars. Transplanting problems can also occur because the root system of the Turkish tree hazel tends to consist of a main tap root with very few lateral roots. Hybrid rootstocks are being developed to circumvent these problems.
Propagation Correct identification of the mother tree and reliability of the source of the mother tree will ensure the propagated tree will be true to type. This is most important with hazelnuts because of the need for genetic compatibility. Also correct timing of pollen shed and receptivity of the female flowers must be reliable for successful nut production. Under no circumstances should hazelnuts for nut production be propagated from seed. The simplest and most common method of hazelnut propagation is mound layering, but tip layering and trench layering techniques are also used. Other propagation techniques include grafting, cuttings and tissue culture. Different hazelnut cultivars are suited to different propagation methods. For instance, some cultivars do not sucker readily, some cultivars sucker readily but do not produce roots readily and others produce suckers that are not flexible enough to bend down. In grafting hazelnut trees, grafts are very slow to callus compared with most other fruit and nut trees. Therefore, providing heat via a grafting tube or heat collar is required to assist callus growth. Sealing the graft union is also necessary to prevent drying. The usual grafting technique used is the whip and tongue graft. As the main aim when grafting hazelnuts is to eliminate suckering, the rootstock mother trees have no suckers for layering so the rootstock is usually grown from cuttings or possibly tissue culture. Propagation by cuttings would be an excellent method of propagating hazelnut cultivars on their own roots and propagating rootstock trees. However, the success rate experienced has been poor. Some propagators have found that the best rooting is achieved from cuttings of firm wood taken in late summer. The cuttings are treated with rooting hormone compound, placed in a coarse medium and provided with bottom heat, overhead misting and good aeration. However problems arose with ceased bud growth and rot at the lateral bud points, and while some roots formed by autumn, no live growing point remained.
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Planting techniques Before planting all weeds are removed and this is particularly important for hazelnut orchards because weeds are difficult to control amongst the low sucker growth that is readily damaged by herbicides. In general, fertilisers should not be applied to newly planted trees. However, incorporating superphosphate into the planting area before planting has been shown to assist tree establishment. Irrigation systems are installed prior to planting. Both drip systems and micro-sprinklers are suitable in hazelnut orchards. Hazelnut trees are planted during winter dormancy. Trees usually arrive from the nursery as bare-rooted whips and roots are kept moist by covering with moist mulch or friable soil. After the tree lines are marked out, the planting holes can be dug. Holes should be at least 250 mm in diameter to accommodate the roots comfortably. A mound is formed in the bottom of the planting hole and the roots are spread out over the mound before filling the hole with soil. Because the combination of hazelnut cultivars is so important to pollination, it is wise to permanently label each tree row, or individual trees where the main crop is interplanted with pollinisers. This saves problems should a tree die and need replacing. To encourage a single trunk rather than a multi-stemmed bush, the top of the tree can be trimmed off at planting. About five good buds are left at the top of the whip and the lower buds can be removed carefully with the fingers. To protect the trunk from sunburn, it can be painted with a white plastic paint that is diluted with water 1:1, or it can be covered with a cardboard or plastic sleeve. Solid tree guards may be required where rabbit protection is needed. It is also beneficial to mulch around the tree to retain soil moisture. Hazelnut trees do not usually require staking.
Management of young trees As most hazelnut trees sucker and the young trunk bark is green, spraying herbicides is not advised. Spray drift from a contact herbicide onto the trunk or sucker growth can burn the tissue and spray drift from a systemic herbicide can kill the tree. Most growers control weeds in the tree line by using a combination of mulching around the base of the trees, mowing down either side of the tree lines and inter-row, and carefully using a nonsystemic herbicide away from the tree. However, some hand weeding is inevitable around the tree trunk and sucker removal is usually done at the same time. A brush cutter can be used but great care is needed to ensure there is no damage to the bark on the trunk or trunks and irrigation equipment. For optimal growth, the soil must be kept moist during the growing season. Mulch will help retain moisture but irrigation is essential during dry weather. Trees are usually fertilised with a high nitrogen fertiliser soon after bud burst in spring. There are three methods of tree shaping: single trunk trees; multiple (2–4) trunk trees; and multistemmed bushes. The most desirable of these in commercial orchards is the single trunk tree. To establish single trunk trees, all sucker growth is continually removed. To establish multiple trunk trees, allow two or three robust well-placed suckers to grow and allow these to form trunks beside the main trunk. Having more than one trunk forms a strong tree for windy sites, however, multiple trunks must be kept free of low branches to allow
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weeding and easy harvest of nuts. If many suckers grow to form a multi-stemmed bush, weeding and harvesting nuts becomes extremely difficult and is not practical for commercial orchards. Multiple sucker growth also creates a crowded canopy and causes shading.
Hazelnut trees can be trained to multi-trunk trees.
Initial canopy training includes pruning in late winter and removal of suckers during summer. For best light penetration and ease of management, four to six well-placed branches are selected to form an open vase shaped framework. This canopy shape allows good light penetration and air circulation.
Management of bearing trees Irrigation Irrigation schedules should be managed according to soil moisture measuring devices. In dry weather during the growing period, young trees may require weekly irrigation but in sandy soil or in very hot weather irrigation may be required more frequently.
Fertilising Tree nutrition is best managed according to leaf and soil analysis. Many factors including the nutrients removed in the crop at harvest affect nutrient requirements. In most orchards, nitrogen and potassium are the main nutrients required by growing and producing trees. Potassium deficiency and excess symptoms can show as scorching of
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the leaf edge. Other nutrients that may be required include phosphorus, magnesium and boron. The trace element boron is usually applied as a foliar spray in spring. While nutrients such as nitrogen and potassium are generally ground spread down the tree lines as granular fertilisers, organic manures can also be spread in this way, and nutrients can be applied using soluble fertilisers through the irrigation system (see Chapters 5 and 6). Leaf and soil analysis is conducted to ascertain nutrient levels and the fertiliser program required. The table below lists the desirable range of nutrients in leaf samples of hazelnut: Element
Desirable level
Nitrogen
2.2–2.5%
Potassium
0.8%–2.0%
Phosphorus
0.14–0.45%
Calcium
1.0–2.5%
Sodium
<0.01
Magnesium
0.25–0.5%
Sulphur
0.12–0.2%
Boron
30–75 ppm
Copper
5–15 ppm
Zinc
15–60 ppm
Source of data: Weir and Cresswell (1993).
Pruning Pruning of the canopy is done in late winter after the catkins have shed their pollen. Because hazelnuts bear on one-year-old wood, care must be taken not to remove too much of the potential crop. Once a vase-shaped canopy is established, the shape is maintained by removing inward-growing branches, crowded and broken branches. An annual light pruning is more desirable than a less frequent heavy pruning because heavy pruning may result in loss of yield. All sucker growth is removed from single or multiple trunk trees and this process is continuous. Suckers are easiest to remove when small. Sucker growth reduces as the trees age.
Weed control Growth of ground cover vegetation is vigorous in irrigated orchards and continuous mowing is required through the growing season to reduce the height of grass in the interrow. Spraying the tree lines and around irrigation emitters with herbicides should be managed carefully to ensure trees are not damaged. All ground cover vegetation in the orchard should be kept short through summer to reduce competition for moisture and ensure a clean floor for harvesting.
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Pests and diseases Pests Aphids. Small green aphids can be found on the underside of young hazelnut shoots and leaves. They suck sap and leave a residue of honeydew. Sooty mould can form on this honeydew. Aphids are usually found in spring and if infestations are severe, spraying with an aphicide may be required to prevent a check in growth of young trees and reduced yields in bearing trees. Big Bud Mite (Phytoptus avallenae). There has been some evidence of this pest in Australia but it is not widespread. This mite is a small eryophid mite that feeds on and within leaf and flower buds and catkins causing enlarged buds during summer. The enlarged buds open prematurely and dry out before falling from the tree. When pistillate buds are attacked, nut production fails. Cultivars that form loose buds are more susceptible to big bud mite than cultivars that form tight buds. Control is difficult but it has been reported that spring aphid sprays reduce mite populations. Birds. Cockatoos and various parrots love hazelnuts and can quickly decimate a crop. While birds are seldom a problem when the trees are young, they soon arrive when nuts are produced and bird deterring measures are essential (see Chapter 6 for bird control measures). Caterpillars. Various grubs may eat the leaves and immature nuts but spraying is seldom required. Mammals. Rabbits and hares can ring-bark young trees and wandering livestock, kangaroos, wallabies and deer can cause severe branch damage to trees in their endeavour to eat the green foliage. Foxes eat nuts on the ground. These pests are most troublesome where the orchard is located close to bushland or forests. Good fencing is essential and tree guards around young trees may also be necessary. Other insects. These include green vegetable bugs, white fly and grasshoppers. Scale insects. This pest can infest young shoots and severe infestations can result in dieback. Scale is controlled by spraying the canopy with white oil during winter dormancy but not during the period when catkins are shedding pollen. White oil can also be sprayed before bud burst in early spring after pollination. Tree borer (Cryptophasa melanostigma). The larvae of this moth bore tunnels into the woody tissue and can ringbark trunk or branches. If the webby sawdust damage is detected early, the hole can be treated with an appropriate insecticide before the tree is permanently damaged.
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Diseases Fortunately the most serious disease of hazelnuts, Eastern Filbert Blight (Anisogramma anomala) does not occur in Australia. Hazelnuts are relatively disease-free in this country, although two diseases may develop and require control in humid or rainy conditions. Hazelnut blight (Xanthomonas corylina). This bacterial disease causes spotting on the husks and lesions on leaves particularly at the leaf tip. Dieback of buds and new shoots can also occur and if infection is severe, young trees may die through trunk girdling. Trees growing in humid locations and trees stressed by poor growing conditions are most at risk. Hazelnut blight can be prevented or reduced by spraying the whole canopy with a copper-based fungicide/bactericide at budburst and again in autumn as leaves begin to fall. Hazelnut blight is seldom a problem where the humidity is low and air circulation is good. Application of copper spray also prevents lichen growth on the tree. Botrytis R (Botrytis cinerea). This fungal disease occurs on the husk and shell of the nuts causing browning of green husks and shell from pre-maturity until after harvest. The disease is seldom a problem in dry seasons.
Harvesting Hazelnuts mature from late summer to early autumn depending on the variety and the location. As the husks yellow, nuts begin to fall and are ready to harvest. Some varieties fall free of the husk and others fall in the husk and require de-husking. Preparation of the orchard floor continues through summer to prevent harvester problems due to a build up
Small finger-wheel harvester for hazelnuts (R. Bean).
Nuts are swept into a windrow in this orchard of single trunk trees. (P. Wheelwright).
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of mulch material. Orchards managed as rows of single trunk trees are the easiest by far when it comes to harvesting. To ensure best quality, hazelnuts should be harvested from clean dry ground and transported to the dryer as soon as possible. In dry weather nuts can remain on the ground for some days without loss of quality, however, both kernel and shell deteriorate rapidly when left on the ground in moist conditions. The hazelnut crop matures gradually and to avoid immature nuts falling, tree shakers are not used early in the harvest season. The fallen nuts are raked manually or mechanically swept into windrows to ease pick up. Harvesters include rotary pick-up, finger-wheel and vacuum pick-up machines. While sweepers and rotary machines require a clean level surface to operate efficiently, finger wheel machines will pick up nuts from slightly undulating terrain. Vacuum harvester hoses can be used on most surfaces and will extract nuts where multiple trunk trees are grown. Young orchards are harvested by hand.
Post harvest The harvested nuts are de-husked and cleaned by hand or mechanically using de-huskers, trommel tables, trash removing drums or hand work via a conveyor. Where possible, blank nuts and nuts with shrivelled kernel are blown or floated off. The cleaned nuts are immediately placed in a dryer. The type of dryer used varies according to the scale of the operation. Most dryers operate via fans blowing air up through the nuts in a silo or bins. Mesh bottom bins can be moved around via fork lift while elevators are required to load nuts into silos. Other types of dryers include tunnel driers, tower dryers, drying rooms and de-humidifiers. Where dryers are installed in an enclosed room, good ventilation is required to ensure moist air is not being recycled. Instruments to measure humidity and temperature are essential for efficient nut drying. These instruments are used to monitor the air at the entry and exit points of the dryer to ensure the humidity
of the in-going air is sufficiently low for Recirculating silo with dehumidifier (Alstonville Steel).
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efficient drying, and to ensure the nuts are not subjected to high temperatures. Many growers have found that ambient air will dry nuts efficiently when large capacity fans are installed in the dryer. It has also been found that when the humidity of the ambient air is greater than 70%, application of some heat to the ingoing air reduces the humidity sufficiently to achieve nut drying. The temperature of the air going into the dryer should be monitored closely. When high in moisture in the first phase of drying, nuts are more readily damaged by heat than when in the last phase of drying. Some growers dry their nuts at temperatures up to 36°C in the late phase while other growers dry at temperatures no greater than 20°C at the beginning and no more than 25°C in the late phase. Drying at low temperatures will ensure best nut quality. (Nut drying is a complex process and technical manuals should be consulted.) The moisture content of harvested nuts can be as high as 20% depending on the weather and locality, and the aim is to reduce moisture content down to 8%. Some processors require a maximum moisture content of around 6%. At 8% moisture content the shell and membrane is quite crisp. The dried nuts are stored in a cool-room or cool situation in a vermin-proof silo or store room. Nuts are graded in a size grader that usually consists of a long drum sheeted in perforated stainless steel graded from small perforations to largest. The nuts pass through the rotating drum falling out in the appropriate holes into bins beneath. Roller size graders may also be used. The following sizes are standard in Australia for hazelnut-in-shell: Small
up to 13.00 mm
Medium
13.01–18.00 mm
Large
18.01–19.50 mm
Very large
19.51–22.00 mm
Giant
over 22.00 mm
Source of data: Hazelnut Growers of Australia (1997): Appendix B.
Sized nuts pass over an inspection line where any defect or damaged nut is removed. Inspection belts are generally fitted with bars that roll the nuts over for full inspection. Nuts are then weighed and packaged into bags or boxes. Hazelnut varieties destined for the kernel market are cracked and all shell is removed. While some growers install their own cracking facilities, other growers transport their nuts to a processing facility. Small nut cracking machines include the use of drum, cone or disc crackers along with aspirators and vibration tables that separate shell from the kernel. All nut processing facilities must satisfy appropriate health regulations.
Marketing Australia imports some 2000 tonnes of hazelnuts annually, mostly as kernel. While this could provide huge scope for import replacement, locally grown product receives a price premium because it has superior flavour. Some imported product is priced at a level
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lower than the present cost of local production. The major hazelnut producing countries are Turkey and Italy that produce some 70% of world production. Hazelnut production in Australia currently totals around 20 tonnes but this is increasing as new plantings come into production. The bulk of this production is marketed as in-shell hazelnuts for local niche markets such as gourmet food outlets, farmers markets and fruit shops. Nut-in-shell has potential for export to out-of-season fresh markets in the northern hemisphere. The market for kernel includes specialist confectionery and baking. For all in-shell markets, the nuts must be large and attractive, and the major markets for kernel require kernel that is easy to blanch and has good flavour. The confectionery market requires kernel that is round and sized between 11–13 mm, or, 9–15 mm. All hazelnut product should be light in colour and be clean and free from mould and shrivelled kernel.
Further reading Australian Nut Industry Council website http://www.nut industry.org.au Baldwin, B. (2000). Selecting pollinators for a hazelnut orchard. Australian Nutgrower 14(3), 16. Baldwin, B. (2001). Hazelnut hybrids and cultivars in Australia. Australian Nutgrower 15(1), 26. Baldwin, B., Gilchrist, K., and Snare, L. (2003). Hazelnut Variety Assessment for Southeastern Australia. Publication No. 03/141. (Rural Industries Research and Development Corporation: Orange, NSW.) Baldwin, B. (2004). ‘Hazelnuts in the New Crop Industries Handbook’. (Rural Industries Research and Development Corporation: Canberra.) Bean, R. (2003). Minimal cost harvesting. Australian Nutgrower 17(1), 21. Hazelnut Growers of Australia Ltd (1998). ‘Hazelnut Growers Handbook.’ (Hazelnut Growers of Australia Ltd: Bathurst, NSW.) Hazelnut Growers of Australia Ltd website http://www.hazelnuts.org.au. Hazelnut Nursery Propagators (1999). ‘The Hazelnut Story.’ (Jaywest International Pty Ltd: Sydney, NSW.) Horticulture Australia website http://www.horticulture.com.au/project Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/htm Salvin, S., Bourke, M., and Byrne, T. (2004). ‘The New Crop Industries Handbook’. Publication 04/125. pp. 393–403. (Rural Industries Research and Development Corporation: Canberra.) Snare, L. N. (2003). ‘Hazelnut Production.’ Agfact H3 1 49. (NSW Agriculture: Orange.) Snare, L. (2004). Hazelnut leaf nutrition. Australian Nutgrower 18(3), 13–17. Weir R., and Cresswell, G. (1993). ‘Plant Nutrient Disorders: Temperate and subtropical fruit and nut crops.’ (Inkata Press: Sydney.)
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13 Macadamias
Background Macadamias are evergreen Australian trees named after the Australian scientist Dr John McAdam. They grow in subtropical rainforests of northern New South Wales and Queensland. Indigenous Australians called the macadamia nut ‘Kindal Kindal’ and while it has been valued as a food for thousands of years, it is only recently that the nut has become the most commercialised bush food. Other names for macadamia nuts include: bauple nuts (because they grew near Mt Bauple), bopple nuts, and Queensland nuts. The first macadamia plantation was established in northern New South Wales in the 1880s but difficulties encountered in cracking the tough shell thwarted development of the industry. Macadamia trees were introduced to Hawaii in 1882 for windbreak plantings and it was there in the 1930s at the University of Hawaii that the commercial potential of the nut was developed. Hawaii soon became the world’s largest producer of macadamia. Commercial orchards were planted in Australia and in 1954 the first mechanised processing plant ensured a viable industry. During the 1970s and 1980s large new plantings extended throughout the high rainfall coastal areas, however, the varieties grown took some eight or nine years to produce an economic crop. Improved varieties were essential for the success of the industry. In 1974 the Australian Macadamia Society was formed and a voluntary levy on growers provided funds for research that included the development of high-yielding hybrids. By the year 2000 Australia was the leading producer of macadamias and production continues to increase as new plantings come into bearing. New technical developments also continue to improve processing efficiency and nut quality. Other macadamia producing countries include Hawaii, South Africa, Kenya, Malawi, Brazil, Guatemala and Costa Rica. The Australian Macadamia Society is based in Lismore in northern New South Wales and has some 800 members. However, macadamia production extends from southern Queensland to northern New South Wales. The major centres of production are: the
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northern rivers region of NSW to the Queensland border; from Gympie and Cooroy to Bauple north of Brisbane; southern Queensland; central Queensland to Bundaberg; far north Queensland on the Atherton Tablelands; the mid north coast of New South Wales; and Western Australia. With production in the order of A$140m at the farm gate and almost A$100m in exports to more than thirty countries, the industry generates considerable funds for extensive promotion and scientific research programs. The outlook is positive and new plantings of macadamia are being established. The increase in production is expected to continue as new orchards come into bearing.
Botany Macadamias belong to the Proteaceae family along with grevilleas and banksias. There are seven species of macadamia endemic to Australia and two are grown for their edible nuts. Cultivars of Macadamia integrifolia are grown commercially and are known as the smooth-shell macadamia. Macadamia tetraphylla is known as the rough-shell macadamia and is often grown in gardens or as rootstock. It has pink flowers and larger, more deeply toothed leaves than M. integrifolia and the leaves retain their spines as they age. The native habitat of M. integrifolia is north of the Queensland/NSW border, while the native habitat of M. tetraphylla is south of the border and it therefore grows well in cooler regions. The macadamia tree is an evergreen tree growing some 15 m tall in forests but usually not more than 10 m in an orchard situation. The trees have a dense rounded canopy of dark leathery leaves. The leaves of M. integrifolia are slightly toothed and pale in colour when young and are arranged in whorls of three. Leaves on M. tetraphylla are sharply serrated, a pinkish colour when young, they are arranged in whorls of four, and the raceme of flowers can be up to 30 cm long. Flowers of M. integrifolia form on a drooping raceme 10–15 cm in length and contain up to 200 white flowers. Macadamia flowers are pollinated by insects. After fertilisation the ovule forms a small green ball that enlarges during summer. When mature, the husk splits and the nut falls to the ground. Macadamia integrifolia is the species grown for commercial nut production and is the focus Fruit and flowers of Macadamia integrifolia. in this book.
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Specific requirements Soil Macadamias grow on a range of soil types but the preferred soil is well-drained loam. While the root system is not deep, the trees perform best on deep soils that are rich in organic matter. Sandy soils can be improved with the addition of mulches, cover crops and manures prior to planting. Clay soils that become water-logged in wet weather are not suitable. A slightly acid soil with a pH of 5.5–6.0 is desirable.
Climate Temperature. The temperature range for maximum growth and production is between 20–25°C. Frost is damaging to trees, particularly new growth and the flowers, and temperatures below –1°C 1°C may kill young trees. High temperatures on the other hand, may reduce foliage growth of young trees, cause premature nut drop and leaf burn, and reduce nut growth. Humidity. While macadamia is a subtropical tree, prolonged wet weather will increase the incidence of disease, particularly blossom blight. Wet weather can also cause problems with pollination and harvest. Therefore, planting trees in fog-prone valleys should be avoided and maintaining good air circulation in the orchard is beneficial. Shelter from wind. As macadamias are forest trees they grow and yield best in sheltered sites. Where trees are exposed to wind, windbreaks should be established prior to tree planting. Rain and water requirements. Unless the rainfall is reliable and 1200 mm or more falls annually, irrigation will be required to maintain growth and production. A store of five megalitres per hectare is said to be necessary for irrigation in some areas. Irrigation is particularly important for establishing young trees and to maintain soil moisture in dry seasons during fruiting. Water quality is important; macadamias do not tolerate salinity.
Location While some macadamia orchards have been planted on hillsides, the steeper the slope, the more difficult and less efficient harvesters and other tractor machinery will be. In choosing a site, consideration should be given to the distance to processing facilities and markets. However, orchards should be isolated from residential areas to prevent problems with neighbours due to machinery noise and chemical use. Orchards adjoining bushland areas may be troubled by large populations of rats and other vermin
Flowering and pollination Peak macadamia flowering is in August and September. Each flower bears both male and female parts and the tubular floret with four stamens is attached to a petal-like sepal. The ovary has two ovules and bears a long style with a small terminal stigma. The style forms
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a loop in its mid-section and pollen is shed within the flower on top of the stigma a day or two before the flower opens. Because stigma receptivity does not coincide precisely with pollen release, in most cases pollen for fertilisation must come from another flower. While single trees produce nuts, more than one variety of macadamia is planted in commercial orchards to ensure cross-pollination. Cross pollination produces more nuts, increases the percentage of first grade kernel, and improves kernel recovery and nut size. Macadamia flowers are insect pollinated. Once fertilised, the ovary swells to a globular fruit with a finely pointed tip. Fine weather that enhances bee activity is important for optimum pollination and bee hives are brought into the plantation during flowering. Factors that affect pollination include weather conditions at flowering and moisture stress on the tree. It has been suggested that a minimum temperature of 18°C during the flowering period will produce maximum yields. After pollination some of the developing fruit falls from the tree. This is known as premature nut drop. The remaining fruit develop singly or in clusters of up to 12 and enlarge over summer. Macadamia nuts are mature on most cultivars by the end of March and nut drop continues from March through to September and as late as October for some cultivars. The pattern of nut drop depends on the cultivar; it can be early, mid or late season.
Orchard layout To maximise sunlight, it is recommended to orientate tree rows in a north–south direction. However, when macadamias are grown on hilly terrain, this may not be possible. On undulating ground, the orchard layout should take into account soil drainage and erosion control, particularly in high rainfall regions. Where excess surface water is likely, most growers plant the trees in rows across the slope at a gradient of 2–5%. On slopes greater than 8%, rows may need to run up and down the slope for safe machinery use. Rows that are not straight may present problems for finger wheel harvesters. The aim when planning tree spacing is to achieve maximum yields over the life of the plantation. While the ideal tree spacing varies with the location, variety and management system, for an early cash flow many growers plant macadamia trees four metres apart in rows seven metres apart giving 357 trees to the hectare. However, where growing conditions are favourable, this spacing will become crowded and require more intensive canopy management than wider spaced trees. Planting trees five metres apart in rows ten metres apart giving 200 trees to the hectare will accommodate more wide-spreading varieties and support the expected 50 year life of the trees, but it will also leave a large part of the plantation unproductive in the early years. At least two varieties are required in each orchard block to ensure adequate crosspollination. Planting only one variety in each row simplifies harvest and other management operations. Plantations can be planted with single rows of alternating varieties, in blocks up to 10 rows wide. Recent research has demonstrated that adequate pollen flow is achieved across five tree rows. Planting in blocks improves management operations that may be variety specific. Layout patterns range from:
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Macadamia cultivars While yield will vary with the season, variety, location and management, by year five most improved varieties should produce one kilogram per tree or 300 kg of nuts in-shell per hectare. By year eight yields would be expected to have increased to 1.8 t ha–1 and by year twelve yields should have increased to around 4.5 t ha–1 and eventually may peak at over 6 t ha–1. Research has indicated that genetic compatibility between varieties can affect yields and kernel quality. Hence it is important to select compatible pollinating partners (see cultivar descriptions below). Extensive work has been done to produce a range of high yielding cultivars and to assess the performance of these cultivars in different regions. Some hybrids resulting from varieties of M. integrifolia × M. tetraphylla have been most successful. Desirable characteristics of cultivars include strong tree growth, low incidence of pests and diseases, low incidence of sticktights and premature germination of nuts, reduced years to bearing, high kernel quality and desirable market requirements.
Some macadamia cultivars The following list is a summary of the main cultivars and their characteristics: 246. Large spreading tree and industry standard; extended heavy flowering; mid season harvest; average kernel size 2.0–2.7 g; 30–36% kernel recovery; compatible pollinisors include: A16, Daddow, A4. 660. Upright tree; late flowering; very early harvest; nuts mainly fall free of husk; average kernel size 1.8–2.2 g; 33–39% kernel recovery; compatible pollinisors include: A16, A4, 849, 246, 814. 344. Upright dense canopy; prone to nut borer and latania scale; mid season flowering; early harvest; average kernel size 2.1–2.4 g; kernel recovery 30–34%; compatible pollinisors include 814, 849, 246, Daddow. 741. Open upright tree; late flowering; early harvest; average kernel size 2.1–2.7 g; kernel recovery 34–48%; compatible pollinisors include: 814, A16, 849, A4.
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A4. Open spreading tree; precocious bearer; heavy late flowering; prone to rat attack; mid season harvest; average kernel size 2.8–3.3 g; 40–45% kernel recovery; compatible pollinisors include: 741, Daddow, 246, 849. A16. Small upright tree; precocious bearer; late flowering, late harvest; average kernel size 2.4–2.9 g; 38–42% kernel recovery; compatible pollinisors include: 741, 246, Daddow, 814,849. A38. Upright open tree; mid season flowering; mid season harvest; average kernel size 2.7 g; kernel recovery 36%. 814. Open upright small tree; low tolerance to husk spot; late flowering; early to mid season harvest; average kernel size 1.7–2.1 g; kernel recovery 34–38%; compatible pollinisors include: 741, 246. 816. Upright tree; late flowering; early to mid season harvest; average kernel size 2.7–3.5 g; kernel recovery 39–45%; compatible pollinisors include: 741, Daddow. 842. Open upright tree; extended flowering, mid season harvest; average kernel size 2.1–2.5 g; kernel recovery 35–42%; compatible pollinisors include: Daddow, 814, 344, 246, 849. 849. Spreading tree; late flowering; mid season harvest; average kernel size 2.5–3.1 g; kernel recovery 40–45%; compatible pollinisors include 741; Daddow, A4. Daddow. Dense spreading tree; prone to nut borer; low tolerance to husk spot; midlate flowering; mid to late harvest; average kernel size 2.2–2.5 g; kernel recovery 35–39%; compatible pollinisors include: 741, A16, A4, 246, 849.
Macadamia rootstocks Currently the cultivar Hinde (H2) and less commonly the hybrid Renown (D4) are the most common rootstocks used. These rootstocks are relatively easy to graft and have proven vigour. Research is continuing into improved rootstock varieties. Rootstock seedlings may be 18 months old when ready for grafting.
Propagation Macadamia trees are often grown from seed for garden purposes but ungrafted seedlings are not planted in commercial plantations. While macadamias can be propagated by cuttings, the industry in Australia is based on grafted or budded trees. For budding and grafting, rootstock seed is germinated in sand with the split side down so that the root grows straight down into the sand. After germination, the young seedlings are transplanted into pots and grown on in a shade house. When the seedlings are ready for grafting the scion wood is collected from proven mother-tree stock. To
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maximise grafting success, the mother tree needs to be cinctured six weeks before collecting the wood. The propagation techniques mainly used in macadamia are side graft that can be done in autumn or early spring, and patch budding that is the preferred method in northern regions. Grafted and budded trees are ready for planting out at about two years of age. In South Africa many macadamia trees are propagated by cutting but trees planted in Australia are generally grafted or budded. Trees grown from cutting have the advantage that sucker growth is true to type but trees are more surface rooted than grafted trees (see Chapter 4 for propagation details). Diagonal side graft
Planting techniques Because macadamias are grown in regions that are likely to experience heavy rain, engineering advice may be required to design a total drainage system to control run-off and prevent waterlogging and erosion. Where the terrain is not steep, the drainage system required may be simpler with contour drains above the plantation and shallow drains between the tree rows. The location, size and type of drains should take into account all management operations, particularly harvest machinery. When earthworks are complete, it is wise to sow a suitable pasture or ground cover to bind the soil and prevent scouring and exposure of tree roots. When trees are young and shading is not an issue, a wide variety of legume and grass species can be grown. Windbreaks of shrubby Australian trees such as Leptospermum and Melaleuca species assist greatly in reducing wind damage to trees. In some plantations bana grass has been planted as windbreaks for young trees but this grass can become uncontrollable and harbour rats and the grass should be removed before trees come into bearing. Tall trees that shade the orchard and drop limbs are not suitable for windbreak plantings. Before planting it is important all weeds are removed from the tree lines because macadamia trees are evergreen and shallow-rooted and they are particularly susceptible to herbicide damage. Where rainfall is inadequate or unreliable, an irrigation system will be necessary. If possible, trees are planted when the soil is moist and the weather calm to prevent drying of the newly transplanted trees. Trees can be planted in autumn but, where frost is likely, trees are best planted in spring. Macadamia trees arrive from the nursery in pots or planter bags. The trees are watered before transplanting and the planting hole is dug so that it is slightly larger than the pot. If the roots are matted in the pot, they should be loosened or cut so that they can be spread out in the soil as the hole is filled in. The tree is positioned in the planting hole so that it is at the same depth as it was in the container. The graft or bud is positioned to face the direction of the prevailing wind
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to reduce wind damage. Branches that compete with the leader are pruned off and where necessary, the trunk is painted with white acrylic paint particularly on the side exposed to the sun, to prevent sunburn. Tying the trees to stakes is not advised because it can result in trunk damage and weak root growth.
Management of young trees Frost can damage young trees and during winter in frost-prone areas, covering the tree trunks with an insulating sleeve made of sisalation or cardboard gives protection. The sleeve also offers some protection from herbicide sprays and rabbits. Weed growth around young trees should be controlled regularly by careful herbicide treatment down the tree lines or by a combination of hand weeding around the trees and mowing. No herbicide spray should come in contact with either the bark or foliage of trees. To avoid tree damage, spraying is done during calm weather and spray drift protectors are fitted to herbicide sprayers. Foliage should also be removed from the lower part of the trunk. Where trees are mulched, the mulch material should be kept clear from the trunk or collar rot may result. While the inter-row strip can be cultivated when trees are young, to avoid root damage the soil should not be cultivated within at least one metre of the trees. After the newly planted tree has its first flush of growth, small amounts of high nitrogen fertiliser are applied around the root zone throughout the growing season. Fertilisers can be applied through the irrigation system or as ground application prior to irrigation. It must be remembered that macadamias are members of the Proteaceae family that have a low requirement for phosphorus. Young macadamia trees are trained to a central leader and the leader and two side branches that form a wide crotch are left to form the initial tree frame. All other branches, low branches and suckers, and branches with a narrow crotch are removed. If no side branches occur between about 50 and 80 cm on the trunk, the top can be headed back to induce side branching.
Management of bearing trees Irrigation Irrigation schedules vary significantly between growing regions. Where rainfall is reliable, irrigation may not be necessary while in low rainfall areas irrigation is essential to ensure good yields and maintain tree health. Adequate soil moisture is particularly important between flowering and nut maturity. Moisture stress during the time of oil accumulation can be particularly damaging to nut quality. Soil moisture measuring devices should be used to determine irrigation schedules.
Fertilising The application of fertilisers is determined by leaf and soil analysis and the nutrients removed in the crop at harvest are also taken into consideration. From year four onwards, samples of mature leaves from the second whorl of leaves are taken in spring before the
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new spring growth. The following table lists the desirable range of nutrient levels for macadamia. Element
Desirable level
Nitrogen
1.4–1.5%
Phosphorus
0.08–0.10%
Potassium
0.4–0.7%
Sulphur
0.16–0.25%
Calcium
0.5–0.9%
Magnesium
0.07–0.10%
Sodium
<0.02%
Chloride
<0.05%
Copper
4.5–10 mg/kg
Zinc
6–15%
Manganese
100–1000 mg/kg
Iron
40–200 mg/kg
Boron
40–75 mg/kg
Source of data: O’Hare et al. (2004): 27.
The timing of fertiliser applications is as important as the rate of application. Nutrients should be applied in frequent small doses and at least four applications should be made through the year. Applying nitrogen in summer is generally avoided. Organic manures and mulches are best applied immediately after harvest to avoid problems with harvest machinery and reduce the risk of microbial contamination of the nuts. Many growers apply a combination of synthetic and organic fertilisers. (See Chapter 6 for more detail on tree nutrition.)
Pruning As trees mature the branches are weighed down with the crop load and they can reduce machinery access down the row. Low branches must be removed to improve access and remove risk to the machine and the operator. This pruning is called skirting and it is usually done using hedging machines. In closely planted orchards or where tree growth is vigorous, the orchard becomes crowded reducing light penetration, air circulation and
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Hedging macadamia to reduce shading (D. Huett).
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access. Penetration of foliar sprays is also less effective. To avoid crowding, a pruning or hedging program should be undertaken to shorten side branches and increase the gap between the canopy rows. Side pruning is best carried out after harvest with a hedging machine. An annual light prune is preferable to heavy pruning. The pruning material can be mulched while green and fresh and left in situ to decompose or it can be removed from the orchard. While tree thinning can also reduce over-crowding, research has shown this is uneconomic.
Ground cover maintenance In high rainfall areas, a covering of vegetation on the ground is important for control of soil erosion. However, the dense evergreen canopy shades the orchard floor reducing ground cover growth. The species of ground cover sown, therefore, must be shade tolerant. Low-growing species are ideal for they compete less for moisture, they require less mowing and better accommodate harvest machinery. Incorporating legume species assists in maintaining nitrogen levels in the soil. Research trials have identified sweet smother grass and Amarillo pinto peanut as the most appropriate species.
Pests and diseases Major insect pests include: Flower Caterpillar, Fruit-spotting Bugs and Nut Borer. Most common diseases include Blossom Blight, Husk Spot, and Trunk Canker. Maintaining an Integrated Pest Management (IPM) system is recommended in all orchards. Close monitoring of the tree status is critical for successful management and this can be done by qualified pest management consultants or independently by growers who know what to look for and the appropriate time of treatment. IPM combines biological, cultural, physical and chemical control methods. In all IPM systems, chemical use is kept to a minimum and when a pest requires spray treatment, it may not necessarily mean the whole orchard requires spraying.
Pests Flower Caterpillar (Homoeosoma vagella). These caterpillars are most active during the main flowering period. The eggs are laid usually before buds open and the larvae eat both buds and flowers preventing nut set. When insecticides are required, spraying should be done at night when bees are absent and care should be taken to avoid using chemicals that harm bees. Other insects to damage flowers include flower thrips (Scirtothrips sp.). Leaf beetles and caterpillars. Various leaf-eating insects may occasionally damage young foliage. Nut Borer (Cryptophleba ombrodelta). The eggs of this pest are laid on the husk and the larvae that hatch tunnel into the developing nut and feed on the kernel. Most severe infestations occur during summer and result in premature nut drop and poor nut quality. Chemical sprays must be applied before the borer enters the husk. Some macadamia varieties are more susceptible than others.
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Rats. While birds such as cockatoos can be troublesome with some thin-shelled cultivars before harvest, rats are the major nut-eating pest and these rodents can cause significant crop loss and damage. The main pest is the black rat (Rattus rattus) that can be distinguished from native rodent species because its tail is longer than its body. The key to preventing rat damage is to put in place a range of rat eradication procedures. Control measures include removing all undergrowth such as bana grass in and around the orchard, keeping the orchard floor clean of fallen nuts, removing any rat nests in trees or on the ground and maintaining permanent bait stations around the orchard. Bait stations can be made by placing rat poison in a car tyre that is covered with a sheet of corrugated iron. Sap-sucking insects. Insects that suck sap from young foliage and fruit weaken the tree and may distort growth. They include aphids, particularly Black Citrus Aphid (Toxoptera citridicus), Latania Scale (Hemiberlesia lataniae), Felted Coccid (Eriococcus ironsidei), and Fruit Spotting Bugs (Amblypelta nitida). Both adult Fruit Spotting Bugs and nymphs suck the sap from developing fruit reducing nut yield and quality. The severity of an infestation can be determined by calculating the percentage of damaged fallen fruit. Chemical control may be required for severe infestations. Other foliage pests include Leaf Miner (Acrocercops chionosema) that is difficult to control without a systemic insecticide. Twig Girdler (Neodrepta lutotactella). The adult of this native pest is a white moth that is active at night. The brown larvae shelter in tunnels of saw-dust covered webbing and they skeletonise leaves and eat bark of stems that results in ringbarking and stem death. These grubs may also tunnel into nuts.
Diseases Blossom Blight (Botrytis cinerea). The spores of this fungus are dispersed by wind and in rainy weather during winter and spring. It is particularly severe in crowded orchards where air circulation is poor. The new flowers turn brown within days and the withered flowers may either drop or remain attached to the tree and develop grey mould. Control is achieved by improving air circulation and spraying with the appropriate fungicide at the first sign of infection. Husk Spot. This disease causes yellow to brownish spots on the husks of full size nuts causing premature nut drop. Incidence can be severe on some varieties in poorly ventilated orchards or in humid or damp locations. Disease incidence may be reduced by removing all crop from the orchard floor after harvest. Spraying can be effective if appropriate fungicides are applied as a preventative spray at monthly intervals after nut set or as soon as the nuts are infected. This is usually some weeks before the tan-coloured spots are visible. Another disease that may damage nuts is called husk rot. Root-rot. There is more than one fungal disease that causes root-rot and subsequent dieback of foliage and tree death. Cinnamon fungus (Phytophthora cinnamomii) is the most common cause of dieback. First signs are usually sparse yellowing foliage and
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stunted growth. This may be followed by death of one or more branches or the whole tree. While some success has been achieved by treating affected trees with appropriate fungicides, prevention is the best method of attack. Ensure the orchard is well-drained and the soil contains a high level of organic matter. Also avoid the use of machinery that may damage roots or the lower trunk because wounds may become an entry point of infection. Also ensure water does not pond under the tree. A related disease called Collarrot (Phytophthora cactorum) results in rotting of the bark at the base of the trunk. This can be prevented by keeping mulch clear of the trunk and ensuring water does not pool near the trunk. Armillaria root-rot (Armillaria mellea) can be a problem on land that has been recently cleared. The fungus rotting the old roots left in the ground invades roots of the tree crop. Armillaria fruiting bodies look like honey-coloured toadstools and they can be seen on the soil surface particularly during autumn and winter. Infected trees eventually die.
Harvesting Macadamia nuts are mature when the inside of the husk changes from white to brown. Macadamias fall both in and out of the husk. Nut fall is prolonged and can extend from February to October depending on the location of the orchard and the variety grown. To ensure efficient pick-up by harvest equipment, the orchard floor is cleaned of sticks and stones and it is mown prior to nut fall. The most popular harvester used is the finger wheel harvester. The disks roll along the ground picking up nuts and other nut-size objects. These harvesters operate best on level land in straight rows but they can operate on sloping country and in rows that are gently curved. The nuts are combed out of the finger wheels and conveyed into a bin via auger.
The finger wheels on the harvester are fitted in sections and can be replaced when necessary.
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Macadamia nuts are harvested every few weeks during the harvest period but the timing is weather dependent. Using machinery in the orchard after heavy rain is not possible on hilly terrain. However, best nut quality is achieved if the nuts are picked up as soon as they fall as nut quality deteriorates when fallen nuts are exposed to hot sun and wet ground. A few varieties of macadamia fail to fall when mature and to assist nut fall, these varieties may require tree shaking or spraying with the chemical Ethephon that causes nut abscission. Tree shaking and chemical abscission to assist nut fall can be used to hasten nut fall of all varieties toward the end of the harvest season.
Post harvest Macadamia nuts are dehusked straight after pick-up to avoid nut deterioration from overA ‘pre-cleaner’ auger can be fitted to the fingerheating. On arrival at the shed, the newly wheel harvester to remove debris. harvested crop passes over a conveyor where foreign debris such as sticks and stones are removed and the nuts then proceed to the dehusking machine. After dehusking, all damaged, discoloured, sprouting and immature nuts are removed before the nuts are elevated to a drying silo. Many growers separate out immature nuts by passing the crop through a flotation tank but this requires experience because some mature nuts may also be floated off. While immature nuts can be separated off via a blower that has the advantage of not wetting the nuts, problems may occur because mature nuts can also be separated out. Immature nuts must be removed because the kernel darkens during roasting and deteriorates during storage. Macadamia nuts may have a moisture content greater than 20% at harvest. Moisture content must be reduced as soon as possible to prevent kernel deterioration. Most growers install on-farm nut silos fitted with forced air fans. In some cases fans are fitted with heating equipment. In the first stage of nut drying ambient air is pumped through the nuts and the temperature of this air is kept low to prevent browning of Macadamia nuts in-shell and kernels.
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the kernel. When the moisture content of the nuts is down to around 10%, the drying temperature can be increased. If heat is used to speed drying, the thermostat should be set to ensure the drying temperature remains below 30°C. Humidity metres can also be used to check the humidity of the in-going air. If the humidity of ambient air is higher than about 60%, heat may be needed to raise the temperature slightly to reduce humidity. Where the drying silo is installed in an enclosed shed, it is important that the circulated air is discharged outside the shed away from the air intake. Nuts can be stored in the silo under fan-forced air for short periods at 10% moisture content, but in some situations nuts may need to be dried down to a lower moisture content. At 10% moisture content, about half the nuts will rattle when shaken. The dried nuts are elevated from the silo into trucks for transport to the processor. Care should be taken during all nut transfer operations to ensure the nuts are not dropped from a height that will fracture the kernel inside the shell. The processor will advise how different varieties of nuts should be delivered. The oil content of mature macadamia kernel is greater than 75% and the kernel has a specific gravity less than water.
Processing Most growers arrange to consign the harvested crop to a processor. The price paid for nut-in-shell is determined by quality factors such as kernel recovery, percentage of first grade kernel and the percentage of reject kernel. High levels of reject kernel will reduce nut price considerably. At the processing plant, the macadamia nuts are cracked and the separated kernel is cleaned and graded. The cracking machinery uses sheer rollers to slice the tough shell from the kernel and the kernel is then separated from the shell fragments. It is most
Final hand inspection of macadamia kernel (G. Hargreaves).
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important that all trace of shell is removed and the kernel is tested for microbiological contamination. The kernel is size graded and colour sorted before cool storage. The percentage of kernel packaged as fresh or sent for further processing and roasting is determined by market demand. Like all nut processing facilities, macadamia nut processors are subject to quality accreditation to ensure the product is of a very high standard. While there are adequate processing facilities to shell and process all macadamia product grown in Australia, a percentage of nut-in-shell is sent to China for hand cracking.
Marketing Production totals fluctuate from year to year. In 2004 macadamia production in Australia exceeded 40 000 tonnes of nut-in-shell. Almost all this product is processed and sold as kernel. Most growers sell their complete crop to the processor who processes and markets the nuts as the demand requires. The nut price and conditions set by the processors may change from season to season but in recent years farm-gate prices have been between A$2.50/kg and A$3.50/kg for nut-in-shell at 10% moisture content and 33% kernel recovery. While the market for nut-in-shell is small because macadamias are so difficult to crack by hand, some growers package and sell nut-in-shell at local markets or niche shops. Another option is to send the nut out to be cracked and processed, and arrange the marketing of the kernel independently. To achieve top returns, quality management is essential at all stages of nut production and processing. Australia supplies around 40% of the kernel traded in world markets. Export of kernel has been estimated at around 8000 tonnes. In 2003, Japan was our largest market at 1962 tonnes followed by the domestic market at 1700 tonnes. The third largest market in 2003 was Europe and the USA was fourth largest. Macadamia production in Australia is increasing and will continue to increase as new orchards come into bearing.
Further reading Australian Macadamia Society website http://www.macadamias.org Australian Nut Industry Council website http://www.nutindustry.org.au Cox, J., Van Zwieten, L., and Ayres, M. (2002). Macadamia husks make compost. Australian Nutgrower 16(1), 38. Drew, H. (2004). Critical issues in spray application in macadamias using ground-based air-assisted sprayers. Australian Nutgrower 18(3), 3–9. Firth, D. J., and McFadyen, L. (2000). Ground covers for erosion control. Australian Nutgrower 14(2), 13. Horticulture Australia website http://www.horticulture.com.au/project Huett, D. (2002). Hedging – Lessons learnt. Australian Nutgrower 16(4), 39. Huett, D. O. (2003). Efficiency of foliar fertiliser application to macadamia. In ‘Proceedings of the 2nd International Macadamia Symposium’. Tweed Heeds, Australia, 29 September – 4 October. pp. 161–163. (Australian Macadamia Society: Lismore, NSW.)
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Kowitz, Y. and Mason, R. (2001). Drying macadamia nut-in-shell on farm. Australian Macadamia Society News Bulletin 28(4), 45–46. McFadyen, L. M. (2003). Canopy management in macadamia. In ‘Proceedings of the 2nd International Macadamia Symposium’. Tweed Heeds, Australia, 29 September – 4 October. pp. 139–144. (Australian Macadamia Society: Lismore, NSW.) Moncor, M. W., Stephenson, R., and Trachoulias, T. (1982). ‘Macadamia flowering’. Tropical Fruit Research Station Report 1982–1983. p. 23. (Department of Agriculture: Alstonville, NSW.) O’Hare, P., Stephenson, R., Quinlan, K., and Vock, N. (2004). ‘Macadamia Grower’s Handbook.’ (Queensland Department of Primary Industries and Fisheries: Brisbane.) O’Hare, P., Loebel, R., and Skinner, I. (2003). Growing macadamias in Australia. (Queensland Department of Primary Industries: Brisbane.) Rhodes, J. (1986). Macadamia pollination. Australian Macadamia Society News Bulletin 13(4): 1–4. Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Stephenson, R. (2001). Selecting better macadamia varieties. Australian Nutgrower 15(1), 14. Vithanage, V., Meyers, N., and McConchie, C. (2004). Maximising the benefits from cross pollination in macadamia orchards. Australian Macadamia Society News Bulletin 31(2), 41–42. Wilkie, J. (2002). On-farm drying using humidity metres. Australian Nutgrower 16(1): 26.
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14 Pecans
Background Pecan trees are native to North America, growing in woodlands in the Mississippi Valley from Indiana and Illinois to Kansas and Texas, and at higher altitudes south to central Mexico. Not surprisingly pecans are known as the American nut and are pronounced ‘p’khan’ in their home country. However, they are usually pronounced ‘peekan’ in Australia. Commercial plantations of pecans extend beyond their native range into New Mexico, Arizona, Alabama, Georgia, Florida and North and South Carolina. Pecans are also grown commercially in Australia, Brazil, China, Israel and South Africa. The first commercial pecan plantation in Australia was established by Deane Stahmann in 1963 near Gatton in Queensland. Stahmann Farm’s larger plantation, ‘Trawalla’, near Moree in New South Wales, was established in 1971. ‘Trawalla’ has achieved some of the highest yields in the world and accounts for approximately 90% of Australian production. Stahmann Farms has led the way for the Australian pecan industry and their processing plant at Toowoomba provides processing and marketing facilities for the whole industry. Pecan plantings in Australia are expanding by about 10% per year. In addition to Stahmann Farm’s pecan plantation at Moree in New South Wales, orchards extend from the Hunter Valley and Nelsons Bay north of Sydney to the mid north coast near Kempsey, and the north coast of New South Wales. In Queensland pecan orchards are located at Munduberra, Gympie, Atherton Tablelands and Beaudesert. Pecan growers total approximately 100 and plantings exceed 180 000 trees covering 1500 hectares. An orchard planting of 20 hectares has been suggested as a minimum to ensure long-term viability. The Australian Pecan Growers Association Inc. is an active industry group formed to represent and support growers and improve pecan production through educational and research activities.
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Botany Pecan trees are also known as hickory trees and they belong to the walnut family Juglandaceae. In fact, the pecan grown commercially for nuts was originally classified as a species of walnut, Juglans illinoensis, but was renamed Hicoria pecan and finally Carya illinoensis. There are about 25 species in the Carya genus and all are large deciduous trees growing over 20 metres tall in forests. They have attractive pinnate foliage that turns golden in autumn. In cultivation trees rarely exceed 20 metres tall. Pecan trees are monoecious producing separate male and female flowers on the same tree. Male flowers are produced in catkins largely formed from lateral buds on one-yearold shoots. The female flowers are borne on the current season’s growth in small terminal green spikes. Like the walnut, pecans are wind pollinated and after the female flower is fertilised, a small green fruit develops, enlarging through summer and maturing in late autumn. Catkin flower buds appear at the base of a new shoot soon after growth begins in spring but the buds do not develop catkins until the following spring.
A typical spike producing several female flowers (A). Bracts may be erect around the stigma (B), or spread out (C).
Catkins and shoots elongate. Each male flower consists of a leafy bract with three to five anthers (A).
Specific requirements Soil While pecan trees are not very fussy about soil type, best production will be achieved when trees are grown on deep well-drained sandy loam such as that found in river valleys and flood plains. A soil pH between 5.5 and 6.5 and a soil depth greater than two metres is ideal. Light sands are not suitable due to their low organic content that results in poor water holding capacity and inability to retain nutrients. On the other hand, heavy clay soils are not suitable either due to poor drainage. Where the clay content of loam is high or soil depth is shallow, raised tree lines, deep ripping and application of gypsum may be required before planting to improve soil structure and drainage.
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Climate Growing season. This can be described as the number of days between the last spring frost and the first autumn frost. For nut production pecan trees require a long growing season. While the trees may grow in southern regions of Australia, nut production will not be reliable unless there are 220 frost-free days and a relatively even day/night temperature. The temperature range within this period should average between 24–30°C. The number of frost-free days required varies slightly according to the cultivar and some varieties require only 180 frost-free days. Chilling hours. Although pecans are warm-climate plants and produce good crops in low-chill areas, they require a period of chilling during dormancy. Chilling requirements vary between cultivars, but 200–300 hours below 9°C is considered adequate to break dormancy in spring. Temperature. While dormant trees will tolerate severe cold, new pecan growth and flowers can be damaged by spring frost and locations prone to late spring frost should be avoided. Severe frost in autumn can also damage immature nuts before harvest. Pecans tolerate high temperatures in summer and for good oil content in the nuts, a daily maximum temperature between 35–40°C over the nut development period is ideal. Humidity. For good pollination and nut development, dry weather in spring and early summer is critical. Pollen dispersal will not be effective when the relative humidity is greater than 85%. Humid conditions also increase the likelihood of disease. Wind. Some pecan cultivars are more prone to limb damage than others and severe wind can damage the developing crop as well as the tree itself. Avoid windy sites or ensure effective wind-breaks are established. Water requirements. While many pecan orchards are located in areas that receive an annual rainfall of 1800 mm or more, a reliable supply of irrigation water is essential because seldom does spring leaf-out and fruit set coincide with good rainfall. It has been suggested that the irrigation requirement for pecans is greater than 6 Ml ha–1. Of course this varies according to age of trees, soil type and climate.
Location Because orchard management involves tractor operated equipment and large harvesters, a level site is easiest to manage. Another factor in assessing the site is access to harvest contractors, processing facilities and markets. Bird control is a fact of life in pecan production and orchards should be isolated from residential areas to prevent problems with neighbours due to noise of bird deterrents and also chemical use.
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Flowering and pollination Female flowers on pecan usually number 2–10 per cluster. In unfavourable conditions, trees may fail to produce many female flowers, but in favourable conditions some varieties may produce large clusters of flowers that may be fertilised and develop into large clusters of nuts. While pecan is self-fertile and a single tree or a planting of a single variety will produce nuts, commercial plantations include at least two varieties to ensure crosspollination. Nuts resulting from cross-pollination are generally larger with a higher kernel percentage. In fact trials conducted under field conditions have shown that crosspollination can produce nuts approximately one-third heavier and 16% larger than nuts pollinated by the one variety. As mentioned above, female flowers are produced on soft new growth while catkins are produced on older wood. Male and female flowers mature at different times on different varieties. Traditionally pecan varieties are classed as Type I (Type A) or protandrous where the catkins shed pollen before female receptivity, and Type II (Type B) or protogynous where the female flowers are receptive before the catkins shed their pollen. Type I varieties include Cheyenne, Cherokee, Cape Fear, Western Schley, Desirable and Caddo. Type II varieties include Shoshoni, Kiowa, Tejas, Wichita, Stuart and Grabohls. However, a more accurate classification of cultivars is required to ensure crosspollination. Cultivars within each of the two types should be further grouped into very early, early, mid, late and very late season flowering cultivars. The time of flowering may also be affected by insufficient chilling in the winter that may delay flowering or high temperatures in spring that initiate early growth. To further complicate the situation, research has shown that pecans exhibit a xenia affect in that the pollen source affects the quality of the kernel. It is advisable to plant more than two different complementary pollinisers, particularly in areas subject to mild winters. Pollinisers for main crops include: Main crop
Polliniser
Cherokee
Chickasaw, Shoshoni
Cheyenne
Shoshoni, Tejas, Chickasaw
Chickasaw
Cheyenne, Cherokee, Western Schley
Kiowa
Cherokee, Western Schley
Shoshoni
Cheyenne, Western Schley
Stuart
Cherokee, Cheyenne
Tejas
Cheyenne, Cherokee, Western Schley
Western Schley
Wichita, Tejas, Kiowa, Chickasaw
Wichita
Cheyenne, Cherokee, Western Schley
Young pecan trees usually produce catkins for a year or two before producing female flowers. Older pecan varieties may take seven years to produce nuts but most new cultivars produce nuts by about year three. However, some varieties of pecan are very
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precocious producing very large crops of nuts on young trees. While this may be desirable for cash flow, it puts the tree at risk in the long term due to a reduction in the ratio of foliage to nuts and this can lead to nutrition problems and dieback. Precocious varieties include Chicksaw, Cherokee and, in some instances, Western Schley. The severity of precocity can be reduced by careful management of fertilisers and by reducing the crop load by tree shaking. Precocious cultivars can be useful for planting as temporary trees to fill out a young orchard. Pollination generally occurs between mid-October and mid-November but this period may be earlier if the weather is hot and dry, or delayed if the weather is cool, rainy, cloudy or foggy. The stigma appears yellow when receptive and browns after pollination. Flowers that have not been pollinated successfully soon fall. When the tree is in full leaf, fruit development is rapid. Greatest fruit expansion usually occurs between December and mid February. The shell then hardens and kernel filling changes from the water stage to a fleshy kernel. As nuts mature from late April to late May, the shuck splits open and releases the nut and it falls to the ground. The foliage turns golden as the autumn nights cool and the tree enters dormancy.
The shuck splits as the nuts mature in autumn.
Orchard layout To optimise pollination, polliniser varieties should be positioned so that the prevailing winds carry the pollen across the orchard. Various layouts have been suggested and in some situations, growers have been advised that polliniser varieties should be spaced at a ratio of 1:3 or 1:4 for optimum production. Another recommendation is that the main crop cultivar is planted in blocks of no more than four rows across and that two or more complementary pollinisers are included. This would ensure cross-pollination when weather or age-related factors alter the timing of flower maturity.
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Example of orchard layout P1 and P2, pollinisers: M, main variety Wind direction P1
M
M
M
M
P2
P2
M
M
M
M
P1
M
M
M
M
P2
P2
M
M
M
M
P1
M
M
M
M
P2
P2
M
M
M
M
P1
M
M
M
M
P2
P2
M
M
M
M
Because the different pecan cultivars produce nuts of different shapes and sizes, the different cultivars usually need to be harvested separately. This is an important consideration in orchard layout. Another factor to consider with tree and row spacings is shading. Because pecan trees are long-lived and become very tall trees, shading can become a big problem, particularity where trees are grown on fertile alluvial soils with good orchard management. Trees should be spaced with their mature size in mind and also their particular growth habit. Pecan cultivars vary in shape from tall upright pyramids to widely spreading trees. While tree spacing can range from 15 × 15 m to 5 × 10 m, many growers plant trees on a square or diamond grid of 10 m or 12 m and plan to remove every second row for timber after about 15 years. Other growers space trees 10 m × 20 m but this leaves a large area of unused ground in the early years unless inter-row cropping is practised. Even where spacing is generous, pruning of the canopy will be required at tree maturity to ensure adequate light penetration in the orchard. However, pruning very tall trees is a difficult and Different varieties of pecans produce different shaped nuts. expensive operation.
Pecan cultivars It is important to select polliniser varieties that shed pollen when the female flowers on the main crop are receptive. Most orchards include at least four varieties to ensure this occurs. Pecan cultivars vary in their suitability of climate and geography. Some are less susceptible to disease in humid coastal locations and some cultivars are better suited to southern areas where the growing season may be shorter. Tree shape is another consideration when selecting cultivars. It is advisable to select a mixture of precocious and late-bearing cultivars. In essence, characteristics to consider when selecting cultivars for a particular location include: fruitfulness, disease resistance, tree vigour, growth and flowering time where spring frosts are of concern, pollination requirements, time of nut maturity, growth habit, and freedom from excessive nut drop and preharvest sprouting. Although
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the disease pecan scab (Cladosporium caryigenum) is not present in Australia, resistance to this disease is included in some cultivars produced through American pecan breeding programs. Pecan nut characteristics include: size of nut; flavour and fibre and oil content of kernel; ease of shelling (e.g. shallow grooves in shell and lack of partition septum); strong shell to avoid excessive damage by birds and machinery but easy to crack, and symmetrical shape.
Some pecan cultivars The flowering time is given for trees 10–20 years of age. Classes reflect pollination and receptivity periods for ensuring cross-pollination. VE, very early; E, early; M, mid; L, late; VL, very late maturity of the respective flower type. Classification is based on flowering data from Wood et al. (1997) and Worley et al. (1992) for trees growing in Georgia USA. These classifications may change with a change in environment. The length of growing season is given in Frost Free Days, FFD. Apache. Flower type II; vigorous tree; good cracking nut with thin shell; excellent rootstock tree; heavy yields. Caddo. Flower type I E/M; FFD, 190–200; nut matures early April; good scab resistance; spreading tree requires minimal shaping; produces small nuts with quality kernel; bears in years 6–8. Cape Fear. Flower type I E/M; FFD, 200–210; nut matures late April; very good scab resistance; grows to good shape with minimum shaping; susceptible to scorch in autumn; good nut quality with full bright kernel; produces from year four. Cherokee. Flower type I E/M; FFD, 190–200; nut matures early April; one of the most prolific varieties; medium scab resistance; vigorous grower and needs early training and pruning to control tree size; produces small to medium nut with quality dark kernel; very precocious bearer; heavy producer but yields can be irregular in coastal areas. Cheyenne. Flower type I E/M; FFD, 180–200; nut matures early April; very good scab resistance; compact growth habit but limbs may split; produces light full kernel that is easy to crack; fruits from years 3–4. Chickasaw. Flower type II E/M; FFD, 180–200; nut matures late March; good scab resistance; vigorous dense growth and needs shaping; may suffer leaf scorch in autumn; produces medium quality nuts; very precocious and bears in years 3–4; tendency to alternate bearing. Choctaw. Flower type II M/L; FFD, 200–220; nut matures mid April; medium scab resistance; vigorous upright growth and requires minimal shaping; produces good quality nuts with large kernel and thin shell; bears by years 6–8.
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Desirable. Flower type I E/M; FFD, 200–210; nut matures mid April; reduced scab resistance; grows to spreading tree and requires minimal shaping; produces large quality nuts with thick shell; slow to bear (6–8 years) but prolific by year 12. Kiowa. Flower type II M/L; FFD, 190–210; nut matures late April; medium scab resistance; needs shaping and is prone to broken limbs; produces excellent quality large nuts; bears from years 4–5. Grabohls. Flower type II E/M; FFD, 200–210; nut matures mid April; poor scab resistance; not suited to coast; grows vigorously and requires training to central leader; produces large quality nut but very thin shell; very precocious bearer beginning in years 3–4. Mahan. Flower type II; vigorous tree sometimes called the Lismore nut; large long nut with thin shell; prolific bearer but nuts may be poorly filled on older trees. Melrose. Flower type II M/M; FFD, 200–210; nut matures mid April; excellent scab resistance; well suited to coast; vigorous upright growth requiring minimal shaping; produces large quality nuts; bears from years 6–8. Mohawk. Flower type II M/M; FFD, 180–190; nut matures early; good scab resistance; vigorous grower and requires minimal shaping; produces large nut but kernel can have lower oil content; bears from years 6–8; yields may fluctuate. Pawnee. Flower type I E/M; nut matures early; tree has strong upright growth; low chilling requirement; produces large plump kernel. Shoshoni. Flower type II E/M; FFD, 180–200; nut matures early April; good scab resistance; strong upright vigorous growth and easy to shape; suits areas of short growing season; produces large quality nuts; prolific in subtropical areas; bears from years 4–6. Sioux. Flower type II E/M; FFD, 190–210; strong growth with many lateral branches; produces quality nuts with high oil content; bears from year six. Stuart. Flower type II E/L; FFD, 180–200; nut matures early April; poor scab resistance; grows strong and upright with minimal shaping; produces quality thick shelled nuts; bears from years 8–10; variety also used as rootstock. Tejas. Flower type II; FFD, 180–200; nut matures mid April; medium scab resistance; strong upright growth; good all-round variety; produces medium size quality nuts with easy-to-crack shell; bears from 4–6 years. Western Schley. Flower type I E/M; FFD, 200–210; nut matures mid April; fair scab resistance; good lateral branching; needs pruning to control tree size; produces medium size quality nuts; bears in 4–5 years; heavy producer.
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Wichita. Flower type II E/L; FFD, 200–210; nut matures mid April; medium scab resistance; prune for good lateral branches; prone to limb breakage; not suited to coastal areas due to the thin shell that is prone to splitting if rain falls during the water stage; produces excellent quality medium size nuts; bears from years 3–4.
Pecan rootstocks Seed for rootstock is artificially stratified in moist sand for a couple of months and some growers also soak the seed for a few days before winter planting. The seed is then sown in moist soil in nursery beds and when germinated the seedlings are grown on for a season prior to budding or grafting. The variety most commonly used for rootstock today is Apache, but Riverside has also been used extensively. Stuart is reported to be a suitable rootstock too. These varieties have been selected because they produce uniform seedlings of good vigour. They also develop a tough bark that is suitable for mechanical shaking.
Propagation Pecans are propagated by both grafting and budding. Grafting is generally done using dormant scion wood. The whip and tongue graft technique is used for small trees and bark grafting is used for larger trees. Summer patch budding is most successful using freshly collected buds and is the best method to produce large numbers of nursery trees and for field budding of trees in the orchard. Patch budding is done in situ on rootstock grown in the orchard or in nursery beds. Summer patch budding is also practised to salvage failed winter-grafted seedlings. It can be used on branches from 10–40 mm in diameter. (See propagation notes in chapter 4.) The rootstock is generally cut back to about 8 cm above the new bud and this stub is used as a stake for tying the new growth. Pecan trees can be top-worked to change to a different variety. Bark grafting is the preferred method and has been successful in New Zealand on trees with a trunk diameter up to 30 cm.
Planting techniques Nursery trees may need to be ordered a year or two ahead of planting. Before the barerooted trees arrive in winter, the soil must be prepared, the tree lines marked and irrigation installed. Pecan trees have a vigorous tap root system and this should be spread out in the planting hole. If roots are too long they should be trimmed and if there is any risk of the disease Crown Gall, the tree and root system in particular, is treated with an anti-gall inoculant. Tree height may be shortened by one half at planting and stakes may be necessary if wind is a problem. Water well after planting but do not apply fertiliser until spring.
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Management of young trees Soon after the young trees leaf out in spring, fertiliser applications begin. Small applications applied at monthly intervals through the growing season are more effective than one large annual dose. The fertilisers applied to young trees are high in nitrogen and should be based on soil and foliar analysis. Many growers find that 30 g per tree of urea per application at year one is adequate and this amount is doubled each year following. Zinc deficiency can result in poor growth of young trees and it has proved important in most orchards to apply a dilute solution of the trace element zinc as a foliar spray in spring. Weeds and grass growth should be mowed regularly to reduce competition for moisture and the mown grass can be spread around the trees as a mulch. Mulching the root zone is particularly beneficial for young trees. Weeds around the base of the trees should be hand-pulled or carefully sprayed with a non-systemic herbicide. Irrigation scheduling should be set by information received from soil moisture probes placed around the orchard. Young trees require frequent watering in hot weather. If the soil dries and trees are stressed, growth will cease and may not restart until the following season. Growers should watch for leaf-eating beetles and sap-sucking insects. Young pecan trees can be pruned in summer, autumn or winter with the aim of training the tree to a central leader with strong lateral branching. In the first season the strongest growing shoot at the tip of the tree is selected as the central leader and other competing branches are removed. Unwanted shoots can be pinched out before they develop. Three or four buds will appear in a cluster at each leaf axil and can be confusing until you know which is which. The largest bud is the primary bud that grows upright with a weak crotch. The secondary and tertiary buds are smaller but they produce shoots at a wider angle and make good lateral branches. Shoots selected as lateral branches should be at least 30 cm apart and closer branches should be removed. The trunk is kept free of branches below 1.2 m to allow for future tractor access and tree shaking machinery. After the first year, the central leader can be cut back to a strong bud each winter. All competing branches are removed. Cultivars that produce wide-spreading branches are more difficult to train to a central leader. If a tree fails to grow, it should be mulched well but left unpruned. Best results are achieved when tree training is combined with good irrigation and fertiliser management.
Management of bearing trees Irrigation Adequate soil moisture is essential for pecan production and soil moisture devices should be monitored regularly and irrigation applied accordingly. Irrigation water should penetrate to a depth of approximately one metre. There are five periods where adequate moisture is particularly important. The first is for early spring growth. The second is during nut enlargement from December to mid February where any shortage of soil moisture will affect the final nut size. The third is the water stage from late January to mid February when the endosperm is liquid. The fourth is for kernel filling from
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February to March when the liquid endosperm develops into a transparent jelly substance. The fifth period during which adequate moisture is essential is at shuck split during April and May. Saline water may cause leaf injury and scorching and it has been reported that irrigation water should not exceed 1.0 dSm–1 (650–700 ppm) in silty clay soils and 2.5 dSm–1 in sandy soils. Saline irrigation water can cause salt accumulation in the root zone.
Fertilising Mature trees are fertilised at least twice in the growing season, usually in early spring and again in early summer. The make-up of the fertiliser is based on the results of soil and leaf analysis taken in January each year. Fertiliser applications primarily consist of nitrogen and potassium and phosphorus can be applied annually. Zinc deficiency is common in pecans and foliar zinc may be required in spring or early summer. It is important that tree nutrition is adequate in summer because when the growth pattern is complete and nuts are mature, pecan and other deciduous trees store carbohydrates for use the following season. The following table lists the normal range of nutrient levels in pecan according to leaf analysis: Element
Desirable level
Nitrogen
2.5–3.0%
Phosphorus
0.12–0.30%
Potassium
0.75–1.5%
Calcium
0.7–2.5%
Magnesium
0.3–0.7%
Sulphur
0.15–0.25%
Sodium
<0.1%
Chloride
<0.5%
Copper
5–50 mg/kg
Zinc
50–100 mg/kg
Manganese
150–500 mg/kg
Iron*
50–300 mg/kg
Boron
20–50 mg/kg
* Leaf analysis is not a reliable guide to iron status. Source of data: Weir and Cresswell (1993).
Pruning Removal of branches that are weak or crowded or compete with the central leader continues as the tree matures. When removed, branches are cut back to the branch collar, that is the swelling in the bark at the base of the branch. This quickly grows over the short stub remaining. All pruning cuts should be painted with a thick white paint to prevent the entry of the wood boring Longicorn beetle larvae. Broken branches and wounds in the bark should also be painted. As pecan trees mature, they tend to develop an alternate bearing pattern and this can be reduced by pruning or hedging and also fertiliser management.
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Pests and diseases In Australia, pecan trees are relatively free from pests and diseases, but a few pests do occur particularly in times of tree stress. Pesticides are used at the optimum time to control severe pest pressure. All effort should be made to encourage beneficial insects and to use non-chemical methods of control such as growing plants that serve as a decoy to a particular pest. In pecan plantations overseas, pecan trees are subject to numerous pests and diseases and one of the most serious is pecan scab. Crown gall is also troublesome overseas and is present in Australia but has not been reported in pecans at this stage. However, growers should watch carefully and report any sign of crown gall infected nursery stock. Trees can become coated in lichen and moss growth that can cause tree stress and this growth can be controlled by spraying with a copper-based fungicide.
Pests Birds. Crows and sulphur-crested cockatoos can damage tip growth on trees and decimate nut crops before harvest. (See chapter 5 for control details.) Bud Mites. These can cause abnormal growth causing multiple growth sprouts known as ‘witches broom’. Cerambycid Borers. These wood-eating borers particularly the Longicorn Beetle (Agrianome spinicollis) also known as Poinciana Longicorn, lay eggs in crevices in the trunk and branches. The larvae grow to large white grubs the size of a finger and bore
Large pruning cuts can provide entry sites for Longicorn Beetle grubs.
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The grubs of the Longicorn Beetle can cause great damage to trees.
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down into the wood weakening the branch and tree making it prone to wind damage. Infestation can be particularly severe in heavily pruned branches or broken branches and trunk injuries. Painting of all pruning cuts with thick plastic paint is recommended to prevent grub entry. Fruit Fly. Adult females of Queensland fruit fly (Dacus tryoni) may sting the green fruit causing ‘stick tight’ nuts. Pecan Stem Girdler (Maroga melanostigma) and Twig Girdler (Nerodrepta lutotactella). The larvae of these native moths feed on the bark and bore into the branch or young trunk, sometimes ringbarking the branches. Branches can be pruned off or an appropriate insecticide injected into each grub hole. Where pecan stem girdler problems are widespread, biological control using the parasitoid Trichogramma sp. has suppressed numbers. Leaf-eating insects. Christmas Beetles, Green Scarab Beetles and Monolepta Beetles can damage foliage and defoliate trees, particularly young trees. They emerge usually after rain and attack the tender new growth. Spraying with an appropriate pesticide may be necessary on severely affected trees. Sap-sucking insects. These include Green Vegetable Bug (Nezara viridula) and Fruitspotting Bug (Amblypelta nitida), aphids, scale and leaf hoppers that are also called jassids. Depending on the severity of infestation, sap-sucking insects may cause mottled foliage and weaken the tree by sucking the sap from the young nuts and foliage. They usually become most troublesome in early summer and sometimes migrate from leafy weeds and leguminous crops nearby. Both the adult leaf hoppers and their nymph stage look like tiny jumping cicadas. They are difficult to control without insecticide but spraying is not necessary if numbers remain low. Aphids and scale insects become troublesome in warm humid conditions. Yellow Peach Moth (Dichocrocis punctiferalis). The larvae are greyish/white with a pink background. They bore into nuts and leave a webby mess of sawdust-like frass. They are more likely to infest trees in subtropical coastal areas.
Diseases Cercospora Spot. This fungus disease can be identified by grey spots with brown margins first on the leaves and spreading to developing fruit in summer and autumn. It occurs after rain in hot weather and can cause nut drop and defoliation. If severe, spraying with an appropriate fungicide may be required. Crown Gall (Agrobacterium spp.). While Crown Gall has not been reported it is present in some nursery situations. Galls begin as soft growths on the base of the trunk or roots and become hard and woody. The bacteria infect the plant from the soil via a wound site. New trees should be treated with an anti-gall product to prevent infection. Infected trees should be destroyed.
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Powdery Mildew. A dry fungus found in spring and summer during humid weather. It forms a white coating on nuts and sometimes foliage.
Harvesting Prior to harvest, the orchard is cleared of all debris and mown to a short turf. Where the growth on the orchard floor is dense, regular mowing should be started many weeks prior to harvest so that the mowing mulch does not clog harvest machinery. Irrigation is stopped just prior to nut maturity to ensure a dry orchard floor for fallen nuts. Nut maturity coincides with a peak in kernel oil content. The first visual sign of nut maturity is when the husk or shuck begins to split open. Different varieties mature at different times between mid April and mid May. The sooner the nuts are harvested and dried after they fall from the shuck, the better the nut quality will be. In dry weather, nuts can remain on the ground for some days without serious nut deterioration but in wet weather nuts should be harvested as soon as possible. Trees are shaken with a tree shaker, either owner operated or contracted, and a pick up of sticks is usually required after shaking. The nuts can then be swept into windrows or raked clear of tree trunks and irrigation equipment by hand. Pick-up harvesters include rotary pick-ups that collect the windrowed nuts, and finger wheel harvesters that pick up scattered nuts. While finger wheel machines will pick up nuts from sloping land and slight depressions, rotary pick-ups require a level orchard floor. Most harvesting machinery is fitted with trash removal equipment that separates out leaves, husks and twigs from the nut crop. The nuts are then transported straight to the dryer. It is usual to shake and harvest nuts from each variety at least twice to ensure both early and late
Some growers use a tree shaker and shake the crop on to ground sheets.
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Tree shaker at ‘Trawalla’ (Stahmann Farms).
maturing nuts are collected. Trees are irrigated after harvest. In addition to an alternate bearing pattern which results in a heavy crop followed by a light crop, pecan yields vary from one variety to another and one plantation to another. However, there have been reports of mature orchards producing up to three tonnes per hectare.
Post harvest From the harvester, the nuts arrive at the dryer in bins or trailers and the crop proceeds over a trommel table or conveyor to remove any debris and reject nuts. The crop is then elevated into the dryer. Efficient drying is critical to nut quality. Nuts that lie moist on the ground for days, or nuts that are
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Reject nuts are removed via a grading belt at this on-farm facility.
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dried too slowly or at too high a temperature may develop off-flavour, darkened colour, mould and they may soon become rancid. Dryers are mostly of silo or bin construction with fans blowing air through the nuts. Drying silos are constructed with mesh floors with fans fitted beneath the floor. Drying bins also have mesh floors and can be positioned over a dryer duct. Bins of nuts can be stacked high and moved via fork-lift while nuts are conveyed into silos via elevators. In all drying systems, humidity meters are essential to ensure the humidity of the air entering the nuts is sufficiently low to dry effectively. Heat can be applied to the in-going air to reduce humidity. Dehydration equipment may also be used. A drying temperature of 38°C is considered maximum but for best quality kernel, drying temperatures should be kept well below this, particularly during the early stages of drying when the moisture content is high. The moisture content of nuts at harvest may be around 20% and they are dried to about 8% moisture content. They may then be dried further down to 4.5% for long-term storage. Most growers dry their nuts on-farm before transporting the crop to the processing facility. This is arranged with the processor before harvest. Samples of nuts are taken to assess quality and payment is adjusted accordingly. The Toowoomba plant owned by Stahmann Farms processes in excess of 5000 tonnes of pecans and macadamias annually producing some 1500 + tonnes of pecan kernel. Growers who grade their own nuts do so in a size grader that usually consists of a long drum sheeted in perforated steel. The nuts pass through the rotating drum falling out the appropriate holes into bins beneath. Roller size graders may also be used. The size-graded nuts then pass over an inspection line where any defect or damaged nut is removed. Inspection belts are generally fitted with bars that roll the nuts over for full inspection. Nuts are then weighed and packaged or proceed for cracking. Cracking pecans is a specialised operation requiring dedicated machinery because in some varieties there is little air gap between the kernel and shell and the kernel is easily crushed. All processing facilities must satisfy appropriate health regulations. Shell from the cracking operation can be processed for garden mulch or used as a fuel or as an abrasive in soaps, paints, polish and wood filler.
Marketing Fluctuating yields due to alternate bearing result in a fluctuation of product for marketing. However Australian pecan production exceeds almost 3000 tonnes of nut-inshell annually and this is rising as new plantings come into bearing. Pecan product produced in Australia is mostly processed and marketed at Stahmann Farms processing plant at Toowoomba in Queensland. The bulk of this product is sold as kernel for the domestic market and export. Because the bulk of the Australian crop is processed by a central processing plant, nut quality standards can be maintained. Another advantage is that growers do not need to purchase their own processing equipment or market their own nuts. Price per kilogram varies according to nut quality but typically in-shell prices at the farm gate in recent years have ranged from A$2.50/kg to A$3.50/kg. The price received by
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growers is dependent on the quality of the kernel, the kernel recovery percentage and the USA market. Prices therefore fluctuate slightly from year to year. Some growers choose to process and sell their nuts locally to shops, wholesalers and at community markets. Retail prices at these outlets can be as much as A$7 per kilogram in-shell. It is considered that there is potential for an increase in both domestic and export markets of pecan and Australia is in a good position to produce export product for northern hemisphere markets out of season.
Further reading Australian Nut Industry Council website http://www.nutindustry.org.au Coombs, M. (1999). ‘Improving pest management in pecan orchards’. HRDC Project No. NT 602. (Horticulture Research Development Corporation: Sydney.) Coombs, M. (2003). Poinciana longicorn. Australian Nutgrower 17(1), 30. Craven, J. (2003). Foliar fertilising at Trawalla. Australian Nutgrower 17(4): 10. Crouch, M. (2001). Cultivar observations at Trawalla. Australian Nutgrower 15(1): 22. Horticulture Australia website http://www.horticulture.com.au/project Johnson, S. (2004). Pecan processing at Stahmann Farms. Australian Nutgrower 18(1): 10. Loebel, R. (Ed.) ‘Starter Kit.’ (Primary Industries: Alstonville, New South Wales). [For the Australian Pecan Growers Association Inc., Lismore, NSW. Publication comprises a series of Fact Sheets.] Loebel, R. (1997). Pecan pollination. Australian Nutgrower 11(3), 2. Loebel, R. (1998). Training young pecan trees. Australian Nutgrower 12(4): 36. Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Sparks, D. (1993). Chilling and heating model for pecan budbreak. Journal of the American Horticultural Society 118(1), 29–35. Sparks, D. (2002). Effect of topography, crop load and irrigation on pecan nut volume and percentage kernel. In ‘93rd Annual Report of the Northern Nut Growers Association’. (Virginia, USA.) Stahmann Farms website http://www.stahmannfarms.com.au Texas Pecan Growers Association. Pecan South. Texas. Weir, R. and Cresswell, G. (1993). ‘Plant Nutrient Disorders: Temperate and Subtropical Fruit and Nut Crops.’ (Inkata Press: Sydney.) Wilkinson, J. (2002). Major pruning in mature trees at Stahmann Farms. Australian Nutgrower 16(2), 10.
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15 Pistachios
Background There are 11 species belonging to the Pistacia genus and they range from small trees to low shrubs. The pistachio species grown for its edible nut is Pistacia vera and it is native to high desert regions in Iran, Afghanistan and central Asia. The habitat of other species extends to Japan, Malaysia, Mexico and southern USA. All species are adapted to cold winters and long hot dry growing seasons. As well as the species grown for nuts, other species are cultivated in gardens for their colourful autumn foliage and some species are used as rootstock in pistachio propagation. Pistachio nuts have been grown commercially in Iran since the 1800s. Other world producers include Australia, Greece, Italy, Syria, Turkey and USA. In the 1970s breeding trials were established at CSIRO Merbein to develop an improved cultivar for Australian conditions and in 1982 the variety Sirora was released. This cultivar promised excellent flavour and green kernel colour and a high percentage of wide split shells that makes the nut easy to open. The scientist behind this work, Don Maggs, has become known as the father of the Australian pistachio industry. Commercial plantings based on the Sirora variety were first established along the Murray River from Swan Hill in Victoria to Loxton in South Australia. Further plantings extend north of the Murray River into New South Wales and as far north as Wagga Wagga and in western Victoria at Kaniva. Smaller orchards are located in eastern Victoria and south-western Australia but summer rain can be troublesome in these districts. The bulk of Australia’s production is produced by two orchards at Robinvale and Kyalite and the bulk of the Australian crop is processed by Australian Pioneer Pistachio Company (APPC) at Robinvale. The presence of this central processing and marketing facility eliminates the need for growers in nearby regions to install on-farm processing. Having a central processor has also been beneficial for the industry as a whole in maintaining quality standards and promotion of Australian pistachios.
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While the bulk of pistachio nuts grown are dried for the snack market, there is a small percentage of product prepared for the fresh pistachio market. This is a popular option when the trees are young and production is small and it is also an option for growers remote from the processing facility The number of growers in Australia totals about 35. There are some 650 hectares of trees planted producing around 1200 tonnes annually on the on/off cycle caused by alternate bearing (see below). Few new orchards are being established and peak annual production of the current planting is estimated to be 1500 tonnes. This is about 50% of the current Australian domestic consumption. The Pistachio Growers Association Inc. was formed in 1985 to represent and support growers. Funded by voluntary contributions, the Association administers the application of funds towards research projects and organises educational activities throughout the year.
Botany Pistachios belong to the Anacardiaceae family along with cashews and mangoes. The pistachio species grown commercially for its delicious nuts is Pistacia vera. Other species of pistachio include P. atlantica and P. terebinthus and these species have been grown for nursery rootstock and pollinisor breeding programs. Pistacia vera is a deciduous tree with rounded leathery pinnate leaves. While trees can grow well over 10 metres in height, in an orchard height rarely exceeds five metres. The pistachio tree is well-adapted to survive long periods of drought having leathery leaves and an extensive root system. Pistachio trees have a long juvenile period bearing few nuts before six years of age. The tree is generally upright although this varies according to variety. Growth habit is characterised by strong apical dominance and a reduction of lateral vegetative buds as trees age. Pistachios bear laterally on one-year-old wood and as trees mature they develop an alternate bearing pattern where there is a reduction of fruit buds on the current season growth. The reason for bearing a heavy crop one year followed by a light crop the next is due to many factors. These include the weather at bloom time and its effect of fruit set, carbohydrate accumulation, light exposure, pruning techniques used, thinning techniques and other environmental conditions. Pistachio trees are dioecious with male and female flowers borne on separate trees. Both male and female flowers are small and petal-less and appear in panicles before the leaves in spring. Pistachios are wind pollinated. After Pistachio fruit turn a beautiful pink as they mature. pollination, the hull and shell of the fertilised
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nuts enlarge to full size and the kernel then develops to fill and split the shell. In early autumn the nuts are fully mature and can be shaken from the tree.
Specific requirements Soil While pistachio trees will grow in most soils, tree size and nut production will be limited when they are planted in shallow soils or light sand or heavy clay. A deep sandy loam having a neutral pH and a rooting depth greater than 60 cm is ideal for commercial nut production. Pistachios are more tolerant of moderately saline and alkaline conditions than other types of nut trees.
Climate Winter chilling. Adequate winter chilling is essential but this varies with variety. A figure of 1000 hours below 7°C is said to be required to produce an even budbreak and good fruit set for Kerman and 600 hours below 7°C. for Sirora. Less hours of chilling usually results in irregular flowering and delayed leaf-out. Summer heat. Pistachios require a long hot summer to achieve fruit maturity. A frostfree period in excess of 200 days is considered necessary to ensure the flowers develop and fruit ripens. Alpine areas and regions too far north or too close to moderating coastal influences may therefore be unsuitable. Wind. While pistachios will tolerate wind, strong wind when trees are young makes tree training difficult, and winds during flowering and heavy cropping can cause reduced yields and broken branches. In most situations, secure staking of young trees is essential. Humidity. The incidence of fungal and bacterial diseases increases with an increase in humidity, particularly in the growing season, and infections are likely to over-winter and recur the following season. Therefore, coastal areas and regions receiving >20 mm of rain per month during summer are unlikely to be suitable for pistachio production. Water requirements. While pistachio trees tolerate periods of drought, for commercial nut production adequate soil moisture is essential during the growing season. Ensuring adequate soil moisture also ensures good development of young trees, good yield and nut quality, and tree health. Currently irrigation water usage ranges from 9 Ml ha–1 in some regions down to as little as 2 Ml ha–1 in other orchards.
Location The shake and catch harvesting machinery used to harvest pistachios is very expensive. Therefore, growers will require access to contract harvesters or be prepared to acquire suitable harvesting equipment. As pistachios perish rapidly after harvest, growers must have easy access to cool storage and appropriate markets if the nuts are destined for the fresh market, or easy access to the hulling and drying processor if the nuts are destined
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for dried snack consumption. Some growers install their own small hulling and drying equipment but this can be costly. Because orchard maintenance involves use of tractor-driven machinery, management is easiest on reasonably level ground. While nuts are not harvested off the ground, harvest machines operate more efficiently on level ground. Bird control is usually required and being located away from residential areas will prevent problems with neighbours due to noise of bird deterrents and also chemical use.
Flowering and pollination The panicles of both male and female flowers are comprised of hundreds of individual flowers enclosed in small scales. The female flowers have a pistil topped with a large three-lobed stigma on a short style, and an ovary that has three carpels, two of which abort. The male flowers have three to five large anthers and release large amounts of pollen. However, the timing of pollen release is variable and more than one variety of male tree is included in an orchard to ensure pollination. The ratio of male trees to female trees in orchards varies from 1:8 to 1:24 depending on the variety, location and size of orchard. While large orchards ( > 25 ha) use a higher ratio, small orchards of a few hectares should use a low ratio to ensure pollination. For successful pollination, female flowers must receive pollen within two days of opening. There are significant differences in the success of pollination between the different male varieties. Blank nuts and non-split nuts are a concern for pistachio growers. Blank nuts result when the embryo fails to grow inside the shell and this can occur during both nut setting and nut filling. Blanking is thought to be influenced by poor tree nutrition and moisture stress. Non-splits are nuts that have a completely closed shell. They are rejected as the split allows consumers to open the nut easily. Non-splits however, can be marketable if they are cracked for kernel. Splitting of nuts in response to kernel growth begins about one month prior to nut maturity. It would therefore seem that factors that promote kernel growth also promote shell splitting. These factors include irrigation management and crop load. It has also been suggested that the non-split characteristic may be transmitted via the pollen. Reports indicate that the percentage of non-split nuts increases with an increase in crop load, and the percentage of blanks decreases with an increase in crop load. Weather conditions can greatly affect pollination and frost, rainy and/or windy weather at flowering can cause poor fruit set. Fruit set is also affected by mild winter temperatures that cause an uneven bud burst in spring. Pistachios have a greater chilling requirement than most other nuts. (See chilling requirements above.)
Orchard layout Because pistachio trees are relatively slow growing, it is tempting to plant trees more intensively than is desired in the long term. However, access for machinery is essential when orchards mature. Harvesters are particularly large and require a wide turning area
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at the end of each row. A turning width of 11 m has been suggested as adequate for sideby-side shake and catch harvesters. As these machines harvest down the row continuously, gaps may be required in long rows to facilitate unloading. Inter-row cropping is one solution for utilising the area between rows when trees are young. An orchard spacing of 5.5 m between rows and 4 m between trees in the row is usual but this varies according to local conditions. Where deep fertile soil is likely to promote greater tree vigour, spacings greater than this may be more suitable, and conversely, spacings less than this may be practical where growing conditions are less favourable. The ratio of male trees to female trees in the orchard is commonly 1:11 but in some orchards a ratio of 1:24 has proved to be adequate. This ratio varies according to the location, the size of the orchard and the male selections used. To ensure there is an overlap in different seasonal conditions, it is usual to include two or three different male selections that shed pollen when the female cultivar is flowering. Significant variation in flowering time occurs when insufficient winter chilling produces spasmodic spring growth. The first male tree is planted in the upwind corner of the orchard and the pattern of female/male continues down the row. Additional male trees can be planted on the windward outside row. Male trees do not produce nuts.
Pistachio cultivars While the pistachio industry in California is based on the cultivar Kerman, Sirora is the main cultivar grown in Australia. This female cultivar appears to have lower chilling requirements, slightly less biennial bearing and produces fewer non-splits than Kerman. While there are a few other nut-producing cultivars grown at the gene bank at CSIRO Merbein and scattered in orchards, the planting in Australia is basically 99% Sirora and 1% Kerman. Research trials continue to evaluate different female selections under Australian conditions. Characteristics included in future selections are likely to be low chill requirements and resistance to the pistachio dieback disease present in some pistachio orchards. Male pistachio trees planted as pollinisers are male selections of Pistacia vera. Most current orchards include the selections known as #3 (original CSIRO name is 15.12) and #4 (14.4) because these cultivars are known to produce an abundance of pollen when the flowers on the female Sirora cultivar are receptive.
Pistachio rootstocks The selection of rootstock for propagation of male and female pistachio cultivars is important for vigour and disease resistance. It is also important to ensure the rootstock used for propagation is compatible with the cultivar to be grafted or budded. Early plantings in Australia were mostly grafted to Pistacia atlantica and later P. terebinthus became a popular rootstock. In recent years, the rootstock of choice has been Pioneer Gold I, a hybrid with P. integerrima parentage that is preferred due to increased vigour. Pioneer Gold also has resistance to Verticillium wilt (see diseases below) that is not a
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problem currently in Australia but potentially could become so. Research into selection of new rootstocks for higher yields, salinity tolerance, drought tolerance and resistance to specific diseases is desirable.
Propagation In large orchards rootstock seedlings are planted and budded in situ to save cost, but in smaller orchards growers usually purchase potted trees budded and grown in a nursery. Before germination, rootstock seed is artificially stratified in a moist medium at 2–4°C for about two months in early winter. In late winter the stratified seed is soaked in water, then placed in moist cloth to germinate under controlled temperature conditions at about 21°C. As soon as a root appears, the seedlings are very carefully transplanted into containers and placed in a greenhouse until they are ready for planting out in the orchard or they are grown on in pots for propagation. Pistachio trees must be transplanted with minimal root disturbance. For winter grafting, dormant wood of the female cultivar is collected from the mother tree in early winter and stored at 2°C in sealed bags. When the trunk of the rootstock seedling is a good pencil thickness (or of similar diameter to the scion wood) it is ready for grafting. Nursery propagators usually graft trees using a wedge graft. To do this a piece of scion stick containing two good vegetative buds is wedged into a slit in the trunk of the rootstock ensuring that there is good cambium contact. The graft is taped firmly and the tree is placed in a greenhouse until the bud grows. The trees are staked and rootstock growth is continually removed. Trees are grown on in a shade house until ready for planting out. Commercial nursery trees are normally two years old at planting. Root disturbance should be minimal when planting rootstock seedlings. Well-grown seedlings are planted out in late winter or early spring and the young trees are tied to a stake to ensure a straight trunk. Budding is preferred to grafting for trees propagated out in the field. If growth is sufficiently vigorous, the rootstock can be budded in mid to late summer. Trees can be either patch budded or T-budded but T-budding is more popular because the bud for a T-bud can be used on a smaller diameter rootstock. (See Chapter 4 for propagation details.) The buds used in summer budding are taken from the mother tree when growth is vigorous and bark slips easily. At this stage the vegetative buds are mature but dormant. All budding and grafting wood is taken from semi-hardened non-fruiting wood. Vegetative buds are usually smaller and more pointed than flower buds and they are found at the base of current year growth. Excessive sap flow can be a problem when budding is done in early summer. When growth of the new bud is visible, the top of the rootstock seedling is pruned back to promote growth of the new bud. As it grows, the new shoot is tied to the stake to prevent wind damage and rootstock growth is continually removed. If bud take is not successful, trees can be budded again until early autumn.
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Planting techniques When soil has been prepared as required (see Chapter 5 on preparing for planting), the tree lines and planting sites are marked and the irrigation system is installed. The tree lines should be completely weed-free prior to planting. Planting of nursery-grown trees is carried out in winter after the risk of severe frosts has passed. Young pistachio trees are very susceptible to damage and should be handled carefully during transplanting. Nursery trees are usually grown in pots. The pots are carefully removed to avoid root disturbance, and the tree is placed in the planting hole high enough to allow for settling of the tree in the soft soil. The tree is watered well and the tip of the tree is pruned back to just over half a metre high. The trunk is then secured between two stakes to prevent wind damage.
Management of young trees Trees that are budded in situ are tied to stakes as the new growth extends to promote a straight tree. Pistachio pruning is quite specific and the recommended techniques should be sourced from the latest industry information. In general, however, trees are trained to an open vase shape with strong primary branches that will carry a heavy crop load and provide sufficient clearance to accommodate harvesting equipment. All pruning is done in dry weather to reduce the risk of disease infection. It has been the practice to pinch out or prune off unwanted low laterals during the growing season to ensure the trunk is clear for tree shaking and machinery access. Some growers leave the low foliage to grow for the first few seasons because they believe the extra foliage promotes a good root system. Tall shoots are headed back to promote primary scaffold branches. This can be done in winter or summer. Pruning that is done in winter promotes more growth than summer pruning which tends to dwarf tree growth. Care should be taken to ensure the weight of branch growth is not too large for the young trunk. Young trees are trained with 2–3 well-spaced branches arising from each primary branch and 2–3 well-spaced branches arising from each secondary branch. These can be tied together if necessary for added support. If the new bud or graft on young rootstock seedlings is not successful, the seedlings can be headed back in winter to promote new growth for re-budding. Poorly grown seedlings should be replaced. For best growth, young trees require frequent watering and fertilising through the growing season.
Management of bearing trees Irrigation While pistachio trees are less thirsty than other nut trees and able to survive periods of drought, irrigation is essential for commercial production. Soil moisture monitoring devices should be used to ascertain frequency and duration of irrigation schedules. As mentioned above, pistachio trees are more tolerant of saline conditions than other nut trees. Rootstock trials in California have shown that trees on selected rootstock such as Pioneer Gold 1, showed no loss of yield when irrigated with water at 8 dSm–1, but
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salinity levels of 12 dSm–1, resulted in yield decreases. Foliage should not come into contact with saline irrigation water. For best quality nuts, best yields and tree health, trees should never be subjected to moisture stress during the growing season. This is particularly important during nut fill in late summer because inadequate soil moisture at this stage can cause a high percentage of non-splits (nuts with shells that do not split open).
Fertilising It is useful from time to time to conduct both soil analysis from the root zone and leaf analysis. This will ensure that a correct diagnosis of nutrition requirements is made and should avoid hidden problems. Leaf samples for analysis are taken from fully expanded leaflets from non-fruiting wood in mid summer. The table below is a guide to the critical nutrient levels in pistachio. Element
Desirable level
Nitrogen
2.5–2.9%
Phosphorus
0.14–0.17%
Potassium
2.0–2.2%
Calcium
1.3–4.0%
Magnesium
0.6–1.2%
Chlorine
0.1–0.3%
Manganese
30–80 ppm
Sodium
n/a
Boron
120–250 ppm
Zinc
10–15 ppm
Copper
6–10 ppm
Source of data: Brown et al. (2000): 3.
As with other nut trees, the frequency of application and amount of fertiliser required varies according to soil type and tree age (see Fertilising in Chapter 6). Frequent smaller amounts of fertiliser are applied on sandy soil than on loamy soils. Nitrogen and potassium are the major nutrients required during spring and summer. Phosphorus is usually applied annually and foliar zinc is applied in spring when a deficiency is indicated by foliar analysis. Boron may also be required as a foliar spray at bud burst due to the fact that pistachio trees have a particular requirement for boron in the pollination process. Boron deficiency has been linked with an increase in non-split nuts.
Pruning As mentioned above, pistachio pruning is very complex. As pistachio trees mature, they develop a strong apical dominance. This means that the buds at the tip are most vigorous and suppress the new growth below. Therefore, if not pruned, the branches grow longer and longer and fruit will be produced further and further away from the trunk. Fruiting trees are pruned each winter to renew fruiting wood, allow light into the
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canopy, and control tree size. Unfortunately mature pistachio trees produce shoots that contain flower buds but very few vegetative buds that can form new branches. So heading back a branch removes apical dominance but new shoots at the pruning point may not be forthcoming. While heading back 3–5 year old branches will reduce fruit-producing wood in the short-term, this is necessary because it stimulates new growth lower in the tree. Careful pruning can reduce the severity of alternate bearing. Pruning will be most effective on healthy vigorous trees and must therefore be done in conjunction with fertilising and irrigation programs. Care should be taken to prevent transfer of disease when pruning. It is recommended to prune only in dry weather and disinfect pruners between trees. Pistachio trees can be mechanically pruned with hedgers but hand pruning is more precise.
Pests and diseases While pistachio trees in Australia do not have serious pest problems, birds can be pesky and one particular disease has caused tree death in recent years.
Pests Birds. Parrots and crows often damage tip growth on trees and decimate nut crops (see chapter 5 for control details.) Sap-sucking insects. Bugs that suck the sap of young foliage and developing fruit include two native species, Rutherglen Bug and Apple Dimpling Bug, and also the Green Vegetable Bug. Damage can result in hull lesion and nut drop. Scale insects. These insects also suck sap from tree foliage but control is relatively simple with white oil.
Diseases Pistachio Dieback. In the 1990s growers noticed patches of gumming on limbs and trunks of mature trees and this was often followed by tree death. A strain of the bacterium Xanthomonas transluscens was identified and has been established as the cause. It has been reported that transmission of the bacterium through budding is unlikely if buds are taken from non-symptomatic trees and standard hygiene for propagation is practised. Research is continuing. Verticillium Wilt (Verticillium dahliae). This fungus can be severe in Californian orchards causing rapid desiccation and death of branches or the whole tree. The impact has been minimised by use of the resistant rootstock Pioneer Gold. Root-rot. Armillaria root-rot (A. mellea) can be prevalent in orchards that are planted on previously treed land because it inhabits old roots present in the soil. During autumn or winter, honey-coloured toadstools can be seen on the soil surface. When orchard trees are infected, growth is reduced, foliage yellows and the tree defoliates. Phytophthora root
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and crown rot (Phytophthora spp.) can also be a cause of tree death in pistachio orchards, particularly where water puddles under trees or trees are temporarily flooded. Aspergillus Fruit Rot (A. flavus). This fungal disease can affect many types of nuts. The disease has been detected in pistachio product overseas but has not been found in Australian pistachios. Nonetheless it can be a risk if harvest is not prompt during wet weather, or if nuts are not stored correctly. Shell staining can indicate early split nuts where the kernel is exposed to infection. Risk of infection is taken seriously because the fungus is associated with the presence of a carcinogenic toxin called Aflatoxin. Botryosphaerea Blight (B. dothidea). While Australian pistachios have been free of this disease, there has been a report of infection in northern New South Wales where summer rain occurs. The disease has spread in Californian orchards where it is now widespread. Infection results in black spotted shoots and leaves that wither and defoliate. Other diseases found in Californian orchards include: Alternaria Late Blight, Botrytis Blossom and Shoot Blight, Phomopsis Blight and Septoria Leaf Spots.
Harvesting At maturity the pistachio hull slips easily off the shell and the colour generally turns a pastel shade of crimson. However, some nuts that are shaded inside the canopy can be yellow and blank nuts tend not to soften in colour. Change in hull colour is closely connected with shell splitting and so it is important to harvest nuts when they are fully mature to ensure maximum shell split. Nut maturity can also be determined by the ease at which the nuts detach from the tree. If the nuts fall when the branch is shaken, they are ready to harvest. Early split nuts occur when the hull is still attached to the shell when the shell splits open. Early-splits are not desirable because the hull splits open and the exposed kernel may deteriorate. As it is rare for the whole crop to mature at exactly the same time, more than one harvest is necessary, usually a week or two apart. Harvest of course, is dependent on fine weather and the availability of harvesting equipment. Fine weather at harvest ensures greatest nut quality and harvest efficiency. Pistachios are small nuts with an open shell so it is important that they do not fall to the ground. Nuts that do fall to the ground may become contaminated if the hull is damaged. The fungus, Aspergillus flavus, inhabits damp soil and has potential to produce a carcinogen called aflatoxin. To avoid contact with the soil, harvesting machinery is therefore based on the shake and catch principle where the tree is shaken and the nuts fall onto a catching frame and are conveyed into a bin. The most popular harvester is the side by side shake and catch machine that is commonly used in large orchards and by harvest contractors. Contract harvesting is an option where transport of the harvesting equipment is practical and where the orchard is of a size for contract harvesting to be cost-effective. Smaller shake and catch harvesters mostly operate with a catching frame not unlike an inverted umbrella that can be opened under the tree canopy when the tree is shaken, and closed for transport to the next tree. For young trees and smaller orchards where the
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Shake and catch harvester (APPC).
expense of a shake and catch machine is not an option, a combination of non-mechanical shaking and catching devices have been used. The simplest is a tarpaulin or length of shadecloth material spread under the canopy and the branches are knocked with long poles. Pneumatic hook shakers are an improvement on this method. These are hand held wands with a pneumatic shaking mechanism run by an air compressor. Slightly more sophisticated catching methods include ground sheets that are attached to a trailer at one end, spread out either side of the tree trunk, and winched or rolled up after nut fall to empty the crop into bins in the trailer. It would be fair to say that the less mechanised the harvest equipment is, the more man power and muscle power required. Whether the nuts are destined for the fresh or dried pistachio market they are harvested by the shake and catch method. In both cases, the harvested nuts must be quickly transported for processing. Fresh pistachios are sold in the hull and so do not need hulling. The fresh nuts are cooled immediately after harvest in a coolroom. Nuts that are destined for the dried pistachio market are quickly transported to the hulling and drying plant. If hulls are not removed within 24 hours, the nuts generate heat and the shell can become stained. The sooner the nuts are hulled and dried, the better quality the nut will be. If there is a delay between harvest and hulling, the bins of nuts should be spread out in a cool-room. Due to substantial alternate bearing of pistachio trees and fluctuating yields, yield data is not meaningful unless averaged over some years. Currently well-managed mature orchards are achieving an average yield of around 3000 kilograms of dried nuts per hectare.
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Post harvest Pistachios destined for the fresh market are cooled straight after harvest. All sticks, leaves and other debris and reject nuts are removed before they are graded, hand sorted and packed into polystyrene fruit boxes. The nuts should be stored in a cool-room at all times.
Unloading pistachio bins for processing at APPC.
Pistachios destined for sale as dried nuts are hulled as soon as possible. The hulling machines remove the hulls and the nuts are then washed to remove any remaining hulls. Floating nuts that are blank are removed and the good nuts are elevated to the drier. Slow drying produces the best quality kernel but this can be difficult when a huge volume of nuts has to be dried at one time. To overcome this problem, a three stage drying process has been developed at the APPC processing plant. From the float tanks, the wet nuts are surface dried with fans and tumblers. They are then aggressively dried for a few hours until ‘shell dry’. The nuts are then slowly dried using ambient air to retain kernel quality. Heat during drying can damage the kernel. The nuts are stable in storage when the moisture content is about 6%. The next step in pistachio processing is removing non-splits via a needle picker machine. The nuts then proceed to the grader that separates nuts into appropriate sizes. To achieve the most uniform grades, the size graders operate via a combination of round and slotted holes. The standard nut sizes for pistachio are: Extra Large: 72 or less nuts per 100 g; Large: 73 to 90 nuts per 100 g; Medium: 91 to 107 nuts per 100 g; Small: 108 or more nuts per 100 g. Quality grades used in Australia include ‘First grade wide splits’ that are light in colour and easy to open, and ‘Natural splits’ that are light in colour with a narrow split. Kernels should be green in colour with sweet flavour.
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Pistachio nuts are dried and non-split nuts are removed.
Discoloured nuts can be removed by electronic sorting equipment and the product is given a final quality sort by hand before packaging as unroasted nuts or proceeding for further processing. The bulk of Australian product is sold as salted and roasted snack nuts. Nuts to be roasted and salted are soaked in brine before proceeding to the roasting ovens. Reject nuts and non-splits can be cracked for their kernel.
Markets Some growers in Australia hull and dry and sell their own product through local farmers markets, mail order and corner stores. However, the bulk of Australian pistachios are processed at the APPC plant at Robinvale in Victoria and marketed by Nut Producers Australia in Adelaide. Approximately 90% of the pistachios produced in Australia is sold as dried, salted roasted nuts. In recent years this market has increased by about 10% per year. This is largely due to the advent of self-serve nut bar displays in supermarkets and the favourable health messages about nuts. The remaining 10% of production is sold as dried unroasted nuts, kernel or as fresh pistachios. The one difficulty that prevails in marketing is the fluctuating production from one year to the next due to the alternate bearing phenomena. At present Australian-grown nuts are replacing imports. The domestic consumption of pistachios is reported to be around 3000 tonne. The farm gate price of pistachios is determined by the world price for the nuts. In recent years growers have received net farm gate returns in the region of A$4750–A$5500 per tonne.
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Further reading Australian Nut Industry Council website http://www.nutindustry.org.au Australian Pioneer Pistachios website http://www.auspistachio.com.au Beede, R., Ferguson, L., Padilla, J.,Tutschulte, H., and Rose, D. (2002). Mechanical hedging and topping in pistachios. Nut Grower Magazine 22(12), 5. (Western Agriculture Publishing Co.: California.) Brown, P. H., and Zhang, Q. (2003). Foliar spray applications at spring flush enhances zinc status of pistachio trees. Australian Nutgrower 17(4), 12. Brown P. H., Kallsen, C., and Beede, R. (2000). Diagnosing and correcting nutrient deficiencies. In ‘Pistachio Production 2000 (Manual)’. (University Extension, University of California, Davis: California, USA.) Facelli, E. (2004). Pistachio dieback update. Australian Nutgrower 18(1), 29. Ferguson, L. (2000). ‘Pistachio Production 2000’. (University of California, Dept of Pomology and Cooperative Extension: Davis, California, USA.) Horticulture Australia website http://www.horticulture.com.au/project Jaynes R. A. (Ed.) (1970). ‘Nut Tree Culture in North America.’ (Northern Nut Growers Association: Connecticut, USA.) Joyce, C. (2004). Pistachios from the field bin to tasty snack nut. Australian Nutgrower 18(1), 5. Maggs, D. H. (1982). ‘An Introduction to Pistachio Growing in Australia.’ (CSIRO Publishing: Melbourne.) Messina, J. (2002). Pistachio propagation. Australian Nutgrower 16(3), 25. Pistachio Growers Association Newsletter (PO Box 34, Paringa, SA 5340). Robinson, B. (1997). Pistachio Nuts. In ‘The New Rural Industries – A handbook for farmers and investors’. (Ed. K. Hyde). pp. 436–443. (Rural Industries Research and Development Corporation: Canberra, ACT.) Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Sedgley M., and Shuraki Y. D. (1997) Pistachio pollination and nut development. Australian Nutgrower 11(1), 12–14. Sykes, S. (2001). Pistachio nut varieties. Australian Nutgrower 15(1), 19. Taylor, C., Facelli, E., Scott, E., Nancarrow, N., Emmett, R., and Sedgley, M. (2004). Pistachio dieback and propagation material. Australian Nutgrower 18(3), 20. Zhang, J. (2004). Stylar End Lesion in pistachio. Australian Nutgrower 18(3), 26. Zhang, J. (2004). Stylar End Lesion in pistachio. Australian Nutgrower 18(4), 37.
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16 Walnuts
Background There are some 20 species of Juglans, the walnut genus, and all are native to temperate and sub-tropical forests of Europe, Asia, North America, and Central and South America. The species cultivated for its sweet nut is Juglans regia, commonly known as English walnut but it is also called Persian walnut and in years past, the royal nut of Jupiter. This species is believed to have originated near the Caspian Sea in Iran and the native habitat extends east from Turkey and Iran to valleys in western China and the eastern Himalayas. A distinctive characteristic of this walnut is that the hull separates readily from the shell. Walnut species known as black walnut are grown for timber production or as rootstock for grafting and there are some sixteen different species. The nuts of black walnuts have a husk firmly attached to a deeply furrowed shell and the kernel is small and fits tightly inside the shell. The species called eastern black walnut (J. nigra), is native to eastern United States and Canada and it is valued for its resistance to root disease and is therefore used in rootstock breeding programs. The timber is also valued for furniture and gunstocks and the green fruit is valued for its medicinal properties. Another black walnut is northern California black walnut (J. hindsii), and this black walnut is also used as a rootstock and a rootstock parent due to its high vigour. Southern California black walnut (J. californica) is native to coastal southern California and grows as a shrubby tree. Two other black walnuts, J. major from Arizona and J. microcarpa from Texas, have been used occasionally as rootstocks in arid and salty soils. Several other species of black walnut hail from Central America. Japanese walnut (J. ailanthifolia) has also been used as a rootstock in propagation. Some species of walnut that hail from tropical regions including Andean walnut (J. neotropica) are evergreen. Cultivars of English walnut are grown for commercial nut production in southern Europe (particularly France, Germany, Italy and Turkey), in the United States (California and Oregon), and in China, India, South Africa, Australia and New Zealand. Figures
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detailing total world production vary. One figure quoted for production in 2003 is 760 000 metric tonnes in-shell and of this China produced 316 000 t., USA produced 283 500 t., Turkey produced 69 000 t., France produced 31 500 t. and other countries made up the remaining 60 320 tonnes. Total production in Australia in 2004 is estimated to have been between 300 and 400 tonnes in-shell. The first commercial walnut orchard in Australia was planted in the Buckland Valley, Victoria in about 1870. Many seedling walnut orchards were also planted by gold miners in the valleys of north-east and eastern Victoria at this time. The first commercial orchard of notable size, Valley Nut Groves, was established by the Schlapp family at Gapstead in north-east Victoria in the early 1920s. In the 1960s and 1970s further commercial orchards were established but most were relatively small orchards. In the mid 1990s the size of new orchards was larger and some very extensive plantings have been established since the year 2000 that have financial backing from agribusiness investors. The largest walnut orchard is the Webster Walnut orchard on the east coast of Tasmania and more recently the Webster managed orchard at Griffith in New South Wales. Prior to the establishment of these orchards, the 2004 tree survey conducted by the Australian Walnut Industry Association revealed that the total walnut trees planted was 240 000 trees. Other recent walnut plantings are located in the Goulburn Valley near Shepparton, the Murray Irrigation Area and in northern Victoria and South Australia. Small plantings are scattered in the Ovens Valley in north-east Victoria, Gippsland in eastern Victoria, southern highlands of New South Wales, Adelaide hills and Riverland in South Australia, and in south-western Western Australia. The walnut industry, therefore, is a mix of scattered older orchards and extensive newer orchards and production is set to increase rapidly as a large number of young trees come into bearing. The Australian Walnut Industry Association was formed in 1990. The Association in partnership with the Institute for Sustainable Irrigated Agriculture at
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Tatura in Victoria, holds annual educational activities for members and walnut research projects have been based at this institute. In 2004 the Association introduced a voluntary levy to raise funds for further walnut research.
Botany Walnuts belong to Juglandaceae, the same family as pecans. While all temperate species are deciduous, subtropical species tend to be evergreen in their native habitat. Black and English walnuts grow up to 30 m tall with aromatic pinnate leaves. The number of leaflets varies with the species. Walnuts are monoecious bearing male and female flowers on the same tree. Male catkins appear in spring and are produced on older wood while female flowers emerge from new terminal shoots in terminal bearing cultivars and also from lateral spurs in lateral bearing cultivars. Walnuts are wind-pollinated and are self-fruitful and nuts can be produced from a single tree if pollen production coincides with receptivity of the female flowers. The English walnut is the nut of commercial production. When fertilised, the female flower swells during summer to form a green egg-size fruit. The shell hardens, the kernel tissue matures and as autumn advances, the green husk covering the nut cracks open and the nut falls to the ground. The autumn leaves soon lose their green colouring and the golden foliage gradually falls and the tree becomes dormant by winter. Walnut fruit.
Specific requirements Soil Walnut trees require deeper soils than other types of nut trees. They grow and produce best crops when planted in organic-rich well-drained sandy loam that has a depth of at least two metres. In recent years walnuts have been planted on shallower soils that have been modified to improve structure and drainage by deep ripping and the addition of gypsum and organic matter. However, these orchards are young and yields long-term are yet to be proven. Walnut trees require a soil of fairly neutral pH between 5.5 and 7.5. They do not tolerate salinity.
Climate Temperature. Walnut production is greatly affected by temperature extremes and susceptibility is largely variety dependent. Frosts that occur in spring when trees are flowering or new fruit are forming can wipe out nut production for that variety that year. On the other hand, high summer temperatures over 38°C can cause sunburn on developing nuts and desiccation of the kernel. Nut quality can be reduced also if nuts are exposed to high temperatures at harvest.
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Chilling requirements. This varies slightly from cultivar to cultivar but generally walnuts require 800 hours below 7°C to produce a uniform bud break and good fruit set. When day/night temperatures fluctuate steeply in winter or when winters are unseasonally mild, bud burst in spring is partly or fully delayed, flowering and nut set are spasmodic and yields are reduced. Humidity. Walnuts are susceptible to bacterial blight and severity of this disease increases with increasing humidity. To maintain blight at a manageable level, walnut production should be located in inland areas of low humidity. Local conditions should also be taken into account to avoid foggy valleys, high spring and summer rainfall and sites where air circulation is poor. Shelter from wind. While good air circulation is beneficial, sites exposed to persistent wind should be avoided. Severe wind will reduce growth and can break the branches and trunk of young walnut trees. Wind can also break limbs of mature trees when the crop load is heavy. Rain and water requirements. Walnuts are thirsty trees, however, walnut production is not suited to areas of high rainfall because high humidity increases the incidence of walnut blight. Irrigation is therefore essential to ensure adequate soil moisture. The water requirement for walnut production varies according to the soil type and climate. If the soil is sandy and summer temperatures are high, maintaining adequate soil moisture may be extremely difficult and tree health and nut quality will be reduced. Where the soil is rich in organic matter and the summer temperatures are mild, water demand is reduced. Irrigation, therefore, can vary from weekly to daily applications and schedules are determined by soil moisture monitoring devices. In dry regions and on sandy soils water storage requirements over 10 megalitres per hectare may be required. Water quality is important because walnuts do not tolerate saline water. Research in California has found that walnut growth and production is likely to be affected on soils with average root zone m–1. salinity greater than 1.5 dSm m–1 when irrigated with water with a salinity above 1.1 dSm
Location The ideal site for walnut production is a level site that provides greatest efficiency for orchard management, particularly for mechanical operations. Harvesting equipment in particular is best suited to a level orchard floor. Gently sloping land may be suitable if appropriate machinery is used. Site selection should also take into consideration access to technical support, contract harvesting and processing facilities, and markets. A site free from vermin is also preferable. However, orchards should be isolated from residential areas to prevent problems with neighbours due to noise from bird deterrents and also chemical use.
Flowering and pollination As catkins elongate in spring, the small male flowers clustered on the catkin mature and the stamens within each flower release pollen. Depending on the cultivar, pollen shed
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may not over-lap the period of female flower receptivity and this is known as dichogamy. There are two types of dichogamy; most walnut cultivars are protandrous which is when pollen shed occurs before the female flower is receptive, however, a few cultivars are protogynous and shed pollen after the female flower is receptive. To maximise bloom overlap and nut set in commercial orchards, at least two cultivars having similar male and female flowering times are grown. In some cultivars, particularly Serr, excess pollen production can cause flower drop. This is known as pistillate flower abscission (PFA), and results in poor crops. Female flowers usually form in groups of two but single and groups of three or more are common. When the pair of feathery stigmas at the tip of the female flower separate from each other they secrete a sticky substance that enhances germination of the pollen. When a viable pollen grain makes contact with the Catkins elongate in spring. receptive surface of the stigma, it germinates and grows to fertilise the ovule in the ovary at the base of the female flower. Walnut pollen is particularly sensitive to dehydration and therefore the weather greatly affects pollen longevity. When fully expanded the stigmas turn brown and are no longer receptive. Flowers that are not fertilised swell slightly then fall to the ground. The fertilised flowers expand in size to form a fruit and the husk tissue thickens. By late spring or early summer depending on the cultivar, the shell forms and the kernel changes from a watery jelly to a firm white flesh. Factors governing nut size include variety, soil moisture, tree health and light interception in the canopy. Walnut trees may produce female flowers in their first year and these may set fruit if pollen from older trees is present.
Orchard layout Tree spacing is a compromise between establishing an initial tree density that will provide maximum profit as soon as possible, and providing sufficient space to sustain tree health and production in the long-term. The ideal tree density varies according to the location, the soil type, the climate, the intended orchard management and the growth habit of the variety planted. One of the most important considerations when establishing a planting
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density is sufficient light penetration to ensure productive fruit wood on the lower canopy when the trees mature. Years ago, when the only walnut varieties available were large terminal varieties such as Franquette and before the introduction of mechanical hedging, tree spacing exceeded 15 metres. Since the introduction of smaller lateral bearing varieties, tree spacing has decreased to as little as four metres. However, planting at this intensity has proved too tight. In recent years a tree spacing of six metres and row spacing of 7–8 metres has proved more appropriate for an orchard on organic-rich loam in an area of low humidity where an upright variety is intended to be hedged mechanically. Where conditions are less favourable, many growers have opted for a tree spacing of at least 7–8 metres and row spacing of 8–10 metres. Whatever the tree spacing, planting trees of one variety per row simplifies orchard management providing adequate space is given at the head of each row for machinery access. Although cross-pollination is not essential in walnuts, more than one variety is included in commercial orchards to maximise nut set and nut size and to reduce the chances of total crop loss if bad weather occurs at a critical time. Planting more than one variety also means that the total crop does not need to be harvested and dried at exactly the same time. It has been found that the spacing of pollinisers at every 10th row is adequate for pollen distribution. Orchard layout must allow for the different varieties to be harvested separately because most markets require named varieties.
Walnut cultivars The range of walnut cultivars has increased greatly in recent years with the introduction of many Californian and some European lateral bearers. Despite their high nut quality, terminal bearing cultivars are seldom planted today because the yield per hectare of lateral bearers is significantly greater. The lead time from planting to nut production can be more than seven years for terminal bearers, however, most lateral bearers produce a harvestable crop in about 4–5 years. The cultivars selected must be appropriate for the climate and micro-climate of the particular site. For instance, where frost is likely in early spring, a late flowering cultivar is necessary to avoid loss of crop due to frost damage at flowering. Late-cultivars are also less prone to bacterial blight in sites where there is fog, high humidity or persistent spring rain. Late cultivars are reported to be less susceptible to damage by codling moth. Some cultivars too are more prone to sunburn, kernel shrivel and darkening of the kernel due to high summer temperatures. Kernel flavour and texture, nut colour and shape and ease of cracking of the different cultivars varies considerably and can affect market demand. Cultivars are also selected for pollinising reasons e.g. the late flowering Franquette is often planted in a block of Howards or Chandlers.
Some walnut cultivars Ashley. Early leaf out and early harvest; lateral bearer; prone to damage from spring frost; blight and codling moth; nut is large with good shell seal and kernel colour; tree moderate size; rounded canopy requires heavy pruning.
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Amigo. Mid season leaf out but early harvest; 75% lateral bearing; nuts are round and size is good but shell seal can be poor; pollen shed follows female blooming; usually grown as a polliniser. Chandler. A Pedro cross; medium to late leaf out and harvest; lateral bearing; nuts are large; oval and good colour but kernel can be pinched; shell is thin and shell seal can be poor; moderately vigorous small to medium upright tree suited to hedgerows. Chico. Precocious lateral bearer; early leaf out and harvest; pollen shed follows emergence of female flowers and is therefore a popular polliniser for many early varieties; prone to damage from spring frost, blight and codling moth; nut is small and tightly filled; tree is small but requires pruning to maintain nut size. Cisco. A Pedro cross; late leaf out and harvest; 77% lateral bearing; nuts are small but colour and shell seal is good; tree is upright, of low vigour and usually grown as a polliniser. Eureka. Old cultivar grown as polliniser for Franquette; leafs out mid season; terminal bearer; heavy well-sealed nuts; kernel susceptible to heat damage; moderate to low yielding; tree is large. Franquette. Old French cultivar; late leafing out and late harvest; not prone to blight or codling moth; terminal bearing; nut has flat base and pointed top; strong well-sealed shell; good kernel colour and flavour; large upright tree. Geisenheim 26. Very late leaf out and harvest; slow to grow and slow to bear; upright tree. Geisenheim 139. Late leafing out and harvest; medium vigour; upright tree once grown as polliniser for Franquette. Hartley. Leafs out mid season; only partly lateral bearing; not prone to blight or codling moth but is prone to deep bark canker; nut is heart-shaped with flat base and pointed top; well-sealed shell; light kernel colour; medium to large spreading tree. Howard. A Pedro cross; leaf out and harvest is late season; precocious lateral bearer; nuts are round and medium to large with good seal and good kernel colour; tree is small to medium and produces high yields in favourable conditions but needs pruning; suited to hedgerows. Lara. Leaf out and harvest is mid to late season; 80% lateral bearing; good yields; large globular nut with rough-textured shell but good shell seal; tree is vigorous and suited to hedgerows.
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Lompoc. Terminal bearer; leaf out and harvest is mid season; nut quality can be affected by high temperatures; large pointed heart-shaped nut; large tree and slow to bear. Payne. Leafs out very early and nuts mature early; prone to damage from spring frost, blight and codling moth; lateral bearer; medium size oval nut; good shell seal; tree is moderate size with rounded canopy, good vigour and requires pruning. Pedro. A Payne cross; leaf out and harvest is mid to late season; 63% lateral bearing; nuts are medium size with fair shell seal but are prone to damage from heat; trees are small and require pruning. Serr. A cross of Payne; early leaf out and early harvest; prone to pistillate flower abscission and damage from spring frost, blight and codling moth; large oval nut with good flavour and kernel colour; large mostly spreading tree; vigorous. Sunland. A Lompoc cross; early leaf out but mid season harvest; prone to damage from spring frost, blight, codling moth and deep bark canker; lateral bearing; large oval nut with smooth well-sealed shell and light kernel colour; tree is moderate in size, vigorous with rounded canopy; produces good yields but nuts are prone to heat damage. Tehama. A Payne cross; early to mid season leaf out and mid season harvest; 65% lateral bearing; nuts are good size but have poor shell seal; trees are upright and large; usually grown as a polliniser. Treyve Mayette. French terminal bearing cultivar; leaf out and harvest is late; nuts are oval with poor shell seal; tree is large and slow to bear; grown as polliniser for Franquette. Tulare. A cross of Serr and Tehama; 72% lateral bearing; leaf out and harvest is mid season; nuts are large with good colour and good shell seal; tree is upright and popular in hedgerow plantings. Vina. A cross of Franquette and Payne; 75% lateral bearing; early leaf out and harvest; prone to damage from spring frosts, blight and codling moth; high yields but nuts darken in hot regions; nuts are pointed; trees are medium size with spreading canopy and require pruning. Wilson’s Wonder. Old terminal bearer; early leaf out and harvest; prone to damage from spring frost, blight and codling moth; nuts large and round but not well filled; poor shell seal and kernel is dark; very large rounded tree slow to bear.
Walnut rootstocks The choice of rootstock is important because walnut trees are susceptible to root disease and some rootstock species are more susceptible to root-rot than others. The popular rootstock in years past was American black walnut, Juglans nigra. Although this species is
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not as vigorous as Juglans hindsii, it has shown some resistance to Phytophthora root and crown rot. Another rootstock once popular was Royal Hybrid that is a cross of J. nigra. English walnut (J. regia) has also been used as a rootstock particularly where blackline disease is of concern but the disadvantages are that the hybrid is the most sensitive to root diseases, salinity and waterlogging. Today the most sought after rootstock is Paradox, a hybrid seedling grown from the fertilisation of J. hindsii flowers with pollen from J. regia. Paradox is seldom available and is expensive. Paradox is the most vigorous rootstock, the most resistant to root and crown rot and the most tolerant of heavy soils. However, Paradox is sensitive to crown gall and blackline virus. (See diseases below.) Today the most commonly used rootstock is the northern California black walnut, Juglans hindsii, because the seedlings are uniform and vigorous and the species has shown some tolerance to saline soils and some resistance to Armillaria root disease. However, this species has not proven to be resistant to Phytophthora root and crown rot and blackline virus. In some instances Japanese walnut (J. ailanthifolia) has been used in rootstock breeding programs.
Propagation Rootstock seed is harvested after nut fall and dried and cleaned. The nuts are stratified in winter by burying in a cold location or by artificial chilling. In early spring, the seed is sown in sandy loam or direct sown in situ for in-field budding. Walnut is difficult to propagate from cutting but semi-hardwood Paradox rootstock has been propagated in this way. For commercial production of bare-rooted trees, rootstock seed is sown in nursery beds and allowed to grow until the trunk is of sufficient diameter for budding or grafting. In cool climates, the rootstock can be grown in containers in a glasshouse situation because this produces the greatest vigour and success rate for grafting and budding. When the rootstock seedlings are of a diameter that matches the scion wood, they are patch-budded in mid to late summer using freshly harvested bud wood from selected mother trees. The bud wood used is firm current season wood and is transported in a moist cool box to prevent drying. Rootstock seedlings that fail to take the bud are rebudded the same season. Walnuts ‘bleed’ sap profusely in spring and early summer and this can prevent successful bud take. In some instances the rootstock seedlings are grafted in winter using dormant bud wood and heat tubes to assist graft callusing. Scion wood for grafting is taken from ripened one-year-old wood in winter and it is sealed, wrapped in a moist medium and stored at 0–4°C. The most common technique use for walnuts is whip grafts and the ideal temperature for callusing is between 22–26°C. Grafting can also be done with dormant scion wood on vigorously growing rootstock seedlings in summer. In all cases, the graft or bud union should be insulated from high temperatures in the first season by shading and insulated by wrapping in paper or foil. To avoid the initial high cost of nursery trees, some growers propagate trees in situ. One or two rootstock nuts are sown at each tree site in the orchard and when germinated, the strongest is selected and nurtured to achieve maximum growth. When of a diameter
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that almost matches the wood to be budded, the rootstock seedling is ready for budding but it is usually not of sufficient size until the second summer. The rootstock trees are then patch budded by experienced propagators and the rootstock growth is headed back to promote growth of the new bud. While in-field propagation is cost-saving initially and trees have the advantage of an undisturbed root system, time to production is longer than planting nursery trees and the success rate can be patchy and result in an orchard of different sized trees. Walnut trees can be top-worked to another variety if necessary. Top-working young trees up to 12 years of age is most successful using the bark grafting technique. Bark grafting can be done in mid to late summer or early autumn when day/night temperatures are most even. The scion sticks are collected when dormant and sealed and stored under refrigeration. (See Chapter 4 on Propagation.)
Planting techniques Nursery grown walnut trees are planted bare-rooted during dormancy in June and July. A good fibrous root system is desirable for good growth. It has been found that an application of a fertiliser containing phosphorus is beneficial prior to planting. A generous hole is dug for each tree and tree roots are kept well covered before planting to prevent drying. Where Crown Gall is a risk, trees should be treated with anti-gall inoculant prior to planting. The tree is placed in the hole, the roots are trimmed to fit, soil is firmed in around the roots as it is planted and the tree is watered. The graft union must be kept above the soil line at the level it was in the nursery. Be sure that the newly planted tree does not settle too low into the soil after watering. Trees are single whips at planting and the top is pruned back to a good bud after planting to match the reduction in root size. This may reduce the tree to half a metre high but growers have found this pruning to produce best growth. Some other growers do no pruning until the summer. In windy sites young trees will require staking.
Management of young trees Good management of a tree in the first years is essential. Walnuts are thirsty trees and soil must be moist at all times during the growing season to sustain new growth. Application of nitrogen and potassium fertilisers in conjunction with irrigation during the growing season has produced excellent growth of young trees. Young trees must be kept free from weed competition. Herbicides are used to control weeds in the tree lines but systemic herbicides should not be used around young trees. Even where non-systemic herbicides are used it is safest to fit cardboard or plastic guards around the trunk and a shield on the weed sprayer to prevent spray drift on trunk and foliage. Some hand weeding may also be required around the tree. Mulching around trees with an organic material such as straw is most beneficial and maintaining adequate soil moisture throughout the growing season is essential. If dryness causes a check in tree growth, growth may not re-start until the next season. The provision of multiple drip emitters around the root zone of each tree is usually adequate for young trees.
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Fertiliser is applied in small frequent applications through the growing season. In many cases growers have reported a deficiency of the trace element zinc that can result in stunted growth. Zinc deficiency can be rectified by applying a foliar spray in spring. To prevent occurrence of bacterial blight, young trees should be sprayed with a copper-based fungicide/bactericide at bud swell and repeated during spring and early summer if conditions are humid. Walnut trees are generally trained to a central leader and this is easier with uprightshaped cultivars than with widely branched cultivars. To train to a central leader, the strongest leader is headed back and all competing branches are removed. Training a strong central leader is particularly important in the early years and competing branches must be removed during the growing season and again in winter. Neck buds and branches that grow to a weak crotch are removed and low-growing side branches are removed or shortened to a temporary stub. As the tree grows, well-spaced side branches with a strong wide crotch that arise above about 1.2 metres on the trunk are selected. Competing side branches are removed. Rootstock growth and suckers are also removed. Pruning can be done in dry weather in summer, autumn or winter.
Management of bearing trees Irrigation Adequate moisture, particularly in the top half metre of soil, is thought to be the most important factor governing nut size and yield. Walnut trees should not be subject to excessive dryness or excessive wetness. Irrigation schedules vary considerably from region to region and in hot, dry climates and sandy type soils irrigation may be required every few days through the growing season while in cooler climates and heavy soil types, irrigation will not be required as frequently. To ascertain exactly when to irrigate and how much water to apply, soil moisture monitoring devices are essential. Increasing the soil organic content by frequent mowing of ground covers has proved beneficial. As walnut trees develop a large canopy and a large root zone, it is important to provide adequate water over as much of the root zone as possible. This is very difficult to achieve with drip systems and most mature orchards, particularly intensively planted orchards, are irrigated via a sprinkler system. To prevent risk of disease, sprinklers should be positioned so that the water does not wet the foliage or the trunk. Good quality water is essential as walnut trees do not tolerate salinity.
Fertilising Fertiliser application generally involves a multi-pronged approach comprising ground application and fertigation. Many growers have found that applying manure in winter is beneficial followed by applications of nitrogen and potassium fertilisers through the growing season and just prior to or immediately after harvest. Tree nutrient status can be assessed through annual leaf analysis and the amount of nutrient removed in the crop at harvest is also taken into consideration. To gain an overall picture of orchard nutrition, soil analysis is also required but at less regular intervals. In some orchards this may
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include the need for foliar application of zinc or boron, or other trace elements may be required. The following table gives critical nutrient levels (on dry weight basis) of walnut leaves in mid summer. Nutrient
Desirable level
Nitogen
2.2–3.2%
Phosphorous
>0.1–0.3%
Potassium
>1.2%
Calcium
>1.0%
Magnesium
>0.3%
Sodium
<0.1%
Chlorine
<0.3%
Boron
36–200 ppm
Copper
4 ppm
Manganese
20 ppm
Zinc
>18 ppm
Source of data: Beutel et al. (1983). [Copyright is held by the Regents of the University of California and this data reproduced with permission.]
Pruning
Pruning to establish a strong framework on young walnut trees is essential.
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Walnut trees are pruned after harvest in autumn or in winter. This avoids the profuse sap flow that occurs in spring and early summer. Pruning involves removing branches with a weak crotch and branches that obstruct the use of a tree shaker and other machinery. As trees mature, sunlight in the canopy must be maintained to ensure nut production in the inner canopy. This is achieved by removing crowded branches and shortening branches. In a hedgerow system, the trees are generally hedged by mechanical hedgers to form a vertical wall or a tapered wall of foliage. As the most productive spur wood on lateral bearing varieties develops after the second season, trees are not hedged every year. Depending on the variety, hedging is carried out on one side of each row every third year to avoid severe crop loss. Hedging more frequently may be required in some precocious varieties. Generally the branches are cut back to the same distance from the trunk each time they are hedged.
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Pests and diseases Walnuts in Australia suffer few pests and diseases compared with walnuts grown overseas. Husk Fly, Orange Navel Worm and Codling Moth are particularly serious pests in other countries. The main disease troublesome in Australia is Walnut Blight and root-rot diseases have also been troublesome in some orchards. The major pest of walnuts is the cockatoo.
Pests Birds. By far the most damaging bird is the sulphur-crested cockatoo. Other birds to attack trees include gang-gangs, corellas, parrots and black cockatoos. While the loss of nuts prior to harvest is most devastating, birds also can damage new buds at any time of the year. Effective bird control measures are essential. (See Chapter 6 for control methods.) Codling Moth. This pest is widespread in walnuts in California where routine insecticide sprays are applied. However, despite the pest being widespread on apples and pears in Australia, only isolated instances have been reported in walnuts and these are generally on old seedling trees and early flowering varieties. The moth lays eggs on the green fruit and the larvae burrow inside and spoil the kernel. Pheromone traps can be hung on trees to monitor the number of male moths. Other forms of pheromone devices that disrupt the mating of the moths have proved effective in apple and pear orchards. Nematodes. Plant parasitic nematodes can infest soil and parasitise roots in walnut orchards and infested soil and planting material must be identified and either avoided or the site fumigated. Leaf-eating pests. In some areas in some seasons, grasshoppers can arrive in great numbers and cause severe defoliation, particularly of young trees. This is usually only a problem when the ground vegetation is dry and walnut foliage is the only green foliage around. Sap-sucking pests. Walnut Scale has been reported in isolated orchards but infestations have not been severe. Walnut Scale appear as brown to grey round shapes closely attached to the bark of young wood. Other insects to suck sap include Erinose Mites also called Walnut Blister Mite because they cause blistered swellings on leaves.
Diseases Armillaria mellea. This soil-borne fungal disease is widespread in Australia. It is particularly troublesome in orchards that have been planted on newly cleared land because the fungus that colonise the old roots left in the soil move on to colonise the healthy roots and basal trunk of orchard trees. The disease is also called Honey Fungus because the fungus present in the roots below ground level produces fruiting bodies above that look like honey brown toadstools. Symptoms include poor growth, listless foliage, dieback of part of the canopy and gradual tree death. On infected wood, white
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fan-shaped mycelium are visible beneath the bark. Research in California has found that the rootstock Juglans hindsii shows resistance and Paradox shows variable resistance. No effective control has been found but avoiding high-risk land and selecting appropriate rootstocks is advisable. Bacterial Walnut Blight (Xanthomonas campestris pathovar juglandis). This disease is widespread in Australia and can be severe in humid locations and in rainy weather. However, control is not difficult where the humidity is low. Symptoms include blackening of or black lesions on new tip growth particularly on young trees, blackened shriveled catkins, leaf spots and black spots on and deforming of green fruit. Nuts that are infected via pollen develop black and mushy and shriveled kernel. Severely affected nuts drop during summer or just prior to harvest. Crop losses can be severe. The bacterium overwinters in the tissue of buds and catkins and as the buds swell in early spring, the disease spreads if conditions are moist i.e. dew, rain, fog. To prevent spread of infection, the whole tree canopy is sprayed with a copper-based fungicide at bud swell and repeated every 7–10 days while moist conditions prevail until the shell hardens. There are commercially prepared copper fungicides but the low cost option is to prepare Bordeaux on-farm by mixing 500 g copper sulphate and 500 g lime to 100 litres of water. The copper sulphate is dissolved in water and added to the tank and the Limil (use fresh Limil) is dissolved in water and added last. A surfactant can be added but this is not essential. Where trees are large, coverage of the whole canopy requires a powerful spray unit. Bacteria tolerant to copper have been reported in California where it has been found that the addition of Maneb (ELF Atochem, North America Inc.: USA) fungicide to the copper preparation improves control of the disease. Copper-resistance has not been reported in Australia. Selection of an orchard site known to have low humidity is crucial to the control of this disease. Bark Canker. There are two canker diseases that sometimes occur. Deep Bark Canker is often the result of tree shaker damage and subsequent infection of the phloem tissue by the bacterium Erwinia rubrifaciens results in deep cracks in the bark that ooze brown sap. Shallow Bark Canker is caused by the bacterium Erwinia nigrifluens and symptoms include water-stained patches on the bark that form a hole and bleed black ooze. This disease does not usually cause tree death. Blackline. This disease has not been reported in Australia. In California it has been established that the disease is caused by an infectious strain of cherry leaf roll virus. The main species affected is English walnut grafted onto Paradox or J. hindsii rootstocks. Symptoms include yellowing and withering of foliage, excessive sucker growth, and cracks in the bark and a black line under the bark at the graft union. Crown Gall (Agrobacterium radiobacter). This disease infects roots of many species of trees. It is not widespread in walnuts in Australia but it would be wise for growers in high risk areas, to take precautions and treat young trees before planting. Symptoms of the disease include formation of galls or spongy tissue of the roots or root crown that results in stunted tree growth and tree death. The bacterium enters the tissue through wounds
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only and trees can become infected in a nursery situation when they are dug for sale or roots are pruned. Infection can be prevented by dipping bare-rooted trees immediately before planting in an anti-gall inoculum. This dip contains a bacterium antagonistic to the disease causing bacterium. Phytophthora. Species of Phytophthora that infect walnuts include P. cactorum, P. citricola, P. cinnamomi and P. parasitica. Phytophthora is a soil-borne fungus that is mobilised in water. Consequently trees growing in soil that is poorly drained or trees that are subject to excess water are most susceptible. It has been reported that roots that have been damaged by burrowing animals or mechanical injury are prone to infection. Symptoms of root and crown rot include yellowing and wilting of part or all of the canopy and excessive catkin production, any of which may be followed by sudden death of the tree. Control is difficult but some growers have found foliar sprays in spring and summer of the fungicide phosphorous acid to be effective. Other growers have reported good results from applying a heavy mulch of lucerne hay and chicken manure to the root zone. Patches of crown rot visible above the soil can be cut out with a sharp knife or hatchet and painted with a paste made from a copper-based fungicide. Where conditions are favourable to phytophthora, selection of rootstocks is important. Research in California has found that Juglans hindsii and J. regia are more susceptible to Phytophthora than J. ailanthifolia, J. nigra and Paradox.
Harvesting Walnuts are ready to harvest in autumn when the hull cracks to release the nut and the oil content of the kernel is high. At this stage the orchard floor is cleaned of all debris and grass is kept mown. Over time the nuts will fall from the tree but this can continue for
When hulls crack the nuts are mature and ready for harvest.
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two months in dry weather. For this reason tree shakers are the most valuable piece of harvest machinery to own because nut fall can occur at the optimum time and this makes pick-up most efficient and produces greatest nut quality. When about 80% of the hulls are cracking, trees to be harvested that day are shaken. Some nuts may fall stuck in the hull but these can be de-hulled by machine or small numbers can be left for a few days for the hull to shrink from the shell so that they can be cracked off by hand or rolling under a boot. A second shake is usually required a week or two after the first shake. Use of Ethephon (Rhone Poulenc) as a foliar spray has proved effective in manipulating the timing of nut fall in trials overseas. Walnuts must be picked up and dried as soon as possible after nut fall preferably within hours. Failure to do so will result in discoloured shell and mouldy kernel in moist weather, heat-affected nuts in hot weather and potential vermin damage. In small orchards or where young trees are harvested, the nuts can be harvested by hand or shaken onto ground sheets and tipped into a bin before the trash is separated out. Another harvest method is to use a finger wheel pick-up machine commonly used in the macadamia industry. However, finger wheels do not work well where the nuts are thick on the ground and may not be suitable where tree shaking is practised. Auger elevators fitted to finger wheel harvesters can break nuts. Generally after tree shaking, the fallen nuts are raked or mechanically swept into windrows and picked up by a rotary harvester. Vacuum pick-up machines are also used. When using sweepers and rotary pick-ups, a level orchard floor is essential. Finger wheel harvesters can be used up and down sloping ground but vacuum harvesters are the most appropriate for undulating situations. Immediately after harvest the nuts are separated out from the hull and leaf debris using equipment such as squirrel cage, trommel table and blower. The nuts are then de-hulled if necessary, washed clean and surface dried before being elevated into a drier.
A tree shaker enables nut fall to occur at the optimum time.
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After tree shaking, the fallen walnut crop is swept into windrows for pick-up by a harvester.
Small quantities of washed nuts can be drained on racks before transport to the drier.
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Post harvest The type of drier used varies according to the scale of the operation. Most driers operate via fans blowing air up through the nuts in a silo or bins. Mesh bottom bins can be stacked and moved via forklift while elevators are installed to load nuts into silos. Other types of driers include tunnel driers, tower driers, drying rooms and de-humidifiers. All drying facilities require ventilation to ensure moist air is not being recycled. Large capacity driers heat the air pumped through the nuts to reduce the drying time, while small scale operations may use ambient air and heat only when required to reduce humidity. However, the air temperature must be monitored closely. When high in moisture in the first phase of drying, nuts are more readily damaged by heat than when in the last phase of drying. Some growers dry their nuts at temperatures up to 36°C in the late phase while other growers dry at temperatures no greater than 20°C at the beginning and no more than 25°C in the late phase to ensure best nut quality. (Nut drying is a complex process and technical manuals should be consulted.) Instruments to measure humidity and temperature are essential to ensure efficient drying and quality kernel. Instruments to determine nut moisture content are also used. The moisture content of nuts at harvest can vary from 20% to 40% depending on the weather and locality. The aim is to reduce the moisture content down to around 8%. At this level the septum that separates the two halves of the kernel is quite crisp. The dried nuts are then stored in a cool room or cool, vermin-proof silo or store room. From the drier nuts are graded in a size grader. This usually consists of a long drum sheeted in perforated steel graded from small perforations to largest. The nuts pass through the rotating drum falling out in the appropriate holes into bins beneath. Roller size graders may also be used. The size grades established by the Australian Walnut Industry Association are: Standard (nuts that fit through a 29 mm hole but not a 25 mm hole), Large (nuts that will pass through Small nut drying silo (Wellwood). a 32 mm hole but not a 29 mm hole), Jumbo (nuts pass through a 38 mm hole but not a 32 mm hole) and Mammoth (nuts that will not pass through a 38 mm hole). Sized nuts then pass over an inspection line where damaged, diseased or marked nuts are removed. Inspection belts are generally fitted with bars that roll the nuts over for full inspection. Blowers can also be included to separate out blank nuts. Nuts are then weighed, packaged and labelled. Nuts that are not marketable in-shell can be cracked for
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the kernel market. The Australian Walnut Industry Association has established size and quality standards for kernel. Some small cracking operations have been set up on-farm, however, large-scale cracking facilities are not available in southern regions of Australia at this stage. Cracking facilities are subject to appropriate health regulations.
Walnut nut-cracking machine (Wellwood).
Marketing In-shell walnuts are traditionally packaged in hessian, poly or net bags ranging between 5–30 kilograms depending on the market use. Most growers market their nuts through wholesalers or direct to fruit markets. A small amount is also marketed at local farmers markets. Growers who have cracking facilities have marketed small packages of kernel direct to restaurants and gourmet shops and larger amounts have been marketed to niche chocolate manufacturers and wholesalers who re-package the product. Some kernel has also been processed for walnut oil. Generally the market for walnuts in Australia has been an in-shell market and premium prices have been achieved because gourmet cooks and consumers who like to eat quality freshly-cracked nuts will pay for this pleasure. However, local production is near to supplying the total domestic consumption of in-shell walnuts, and export in-shell markets and kernel markets for locally grown product are now being researched. While the domestic requirement for walnut kernel is primarily supplied by imported kernel,
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Australian-grown kernel is not expected to replace much of this volume because of the price differential. In recent years Australian growers have been obtaining between A$4 and A$6 per kilo for in-shell walnuts on the local market while wholesalers can purchase imported in-shell product at prices significantly less than this. Imported kernel is available at a very low price. While the quality of imported kernel can not be compared with locally grown kernel, the market is primarily for baking and confectionery and many processors are not willing to pay a premium for local high quality product. From the 1980s to 2000 annual production of walnuts in Australia remained between 100 and 200 tonnes. As new areas of young walnuts began to reach bearing age, annual production increased to about 400 tonnes in 2004 and significantly greater increases are expected in the next decade. It is inevitable that this will result in some price reduction at the farm gate. However, it is hoped that niche or export markets can be found that will soften the price drop. The health message should also produce an increase in domestic consumption. With the expected increase in production, large-scale processing and cracking facilities are likely to be developed and the expected increase in levy funds should sustain a high level of research and promotion for the whole industry.
Further reading Adem, H. (2002). Pruning and training for hedgerow. Australian Nutgrower 16(2), 3. Adem, H., and Jerie, P. H. (2004). Walnut industry – Research and best practice implementation. Research Project DAV–164A. (Rural Industries Research and Development Corporation: East Melbourne, Vic.) Adem, H., Jerie, P. H., Aumann, C. D., and Borchardt, N. (2000). High yields and early bearing for walnuts. Research Project No. DAV–73A. (Rural Industries Research and Development Corporation: East Melbourne, Vic.) Allen, A. (1986). ‘Growing nuts in Australia.’ (Night Owl Publishers: Shepparton, Victoria.) Australian Nut Industry Council website http://www.nutindustry.org.au Beutel J., Urie K., and Lilleland O. (1983). Leaf analysis for California deciduous fruits. In ‘Soil and plant tissue testing in California’. pp. 15–17. University of California Division of Agriculture and Natural Resources, Bulletin 1879. Germain, E. (1981). ‘The Walnut.’ (National Institute for Agricultural Research (INRA): Paris.) Horticulture Australia website http://www.horticulture.com.au/project Kenez, J. E. (Ed.) (1998). ‘Guide to establishing a walnut orchard in Australia.’ (Australian Walnut Industry Association Inc.: Melbourne.) Kenez, J. E. (Ed.) (1998). ‘Walnut Quality Management Guide.’ (Australian Walnut Industry Association Inc.: Melbourne.) Kenez, J. (2001). Walnut varieties in Australia. Australian Nutgrower 15(1), 5. McNeil, D. (2002). Walnut blight research. Australian Nutgrower 16(2), 35. Ramos, D. E. (Ed.) (1998). ‘Walnut Production Manual’. (Division of Agriculture and Natural Resources: University of California, Oakland, California, USA). Rand, P. (1998). Irrigation, nutrition and disease management strategies to maximise yield and quality of walnuts. Project NT95003. (Horticultural Research and Development Corporation: Sydney.)
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Rural Industries Research and Development Corporation website http://www.rirdc.gov. au/reports/index.htm Titmus, L. (2001). Which walnut variety? Australian Nutgrower 15(1), 6. University of California (1993). Integrated Pest Management for Walnuts. Publication 3270. (Division of Agriculture and Natural Resources: University of California, Oakland, California. USA.) Vavasour, B. J. (1984). ‘Growing Walnuts.’ (Government Printer: Wellington, New Zealand.)
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17 Other tree nuts
Brazil nuts Brazil nut, Bertholletia excelsa, is a member of the Lecythidaceae family and grows in the tropical forests of Amazonia. These Brazil nut forests are known as ‘castanhais’ and occur in the Guianas, Amazonian Brazil, south-eastern Colombia, southern Venezuela, eastern Peru and northern Bolivia. Brazil nut trees are not grown in Australia but as it is an important tree nut on world markets, a brief overview is included in this book. Brazil nut trees are large deciduous trees growing to 50 m tall and they have a life span of several hundred years. The trees bear leathery leaves and spikes of attractive white flowers that may form large woody ball-shaped fruit containing many tightly packed seeds or Brazil nuts. Brazil nut flowering occurs during the dry season and extends into the wet season. Toward the end of the rainy season, the leaves of the trees begin to fall. The new foliage grows at the base of the previous year’s flower stems and the new flowers form at the tip of the new growth. Brazil nut flowers open for a couple of hours in the early morning and are pollinated by large insects particularly ‘orchid bees’ that inhabit the forest. Pollinating the flowers involves opening the hood of the flower and few insects are able to do this. It is thought that most seed set is the result of cross-pollination. After fruit set, a coconut-sized fruit develops over about 15 months. While maturing on the tree, the fruit may be attacked by forest birds but once mature the fruits fall to the ground. Gatherers from forest communities wait until all the fruit has fallen to avoid being hit while working under the trees. Brazil nut fruits weigh between 0.5 and 2.5 kg and have a tough woody outer shell containing between 10 and 25 nuts. The agouti, a large forest-dwelling rodent, has teeth of sufficient strength to open the fruits. Very often the agouti takes the fruit over 400 m from the tree to gnaw through the shell and consume the seeds. The agouti may also bury some seeds and these may grow if they are not consumed before germination. The number of fruits produced by mature trees
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Brazil nut.
ranges from 63–216. Trees tend to be biennial bearing and a year of high yield is often followed by a year of poor yield. After collecting the fruits from the forest floor, the gatherers carry them to local dealers then to peeling and bagging factories before export. The harvested fruits are split open, washed and dried. In Brazil the nuts are dried in rotary driers while in Bolivia and Peru nuts are dried on slatted floors. The nuts are shelled either by the autoclave process using steam to expand the shell and loosen the inner skin, or by soaking for 24 hours to expand the shell to ease manual cracking. The nuts are graded then oven dried or sundried before storage. While seedling trees begin to fruit at 12–16 years and achieve maximum production after 25–30 years, it is reported that grafted trees start producing fruit at year six. At the Agricultural Research Centre of Humid Tropics in Brazil researchers are working to identify superior selections and propagate grafted trees for commercial plantations. Brazil nut trees grow best on deep well-drained alluvial soils on ground not subject to flooding. While Brazil nut product remains primarily gathered from wild trees, several Brazil nut plantations have been established. Pollination problems have been experienced in plantation trees and yields have not been comparable with the yields produced by trees grown in natural forests. This is thought to be due to the lack of the pollinating insects in plantations and to solve this problem, more recent plantations have included plants that provide a food source for specific pollinating insects. Plantations have also been established as rows of trees within the natural forest. One of the most extensive plantations is Fazenda Aruana located
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in Amazonas State, Brazil. This is a former cattle ranch and while predictions are promising, the few thousand hectares of plantation have not yet proved viable. Brazil nut is one of the most important economic plants of the Amazon, yet deforestation in the Amazonian rainforest has resulted in a significant reduction in crops harvested. Over a ten year period from 1970 to 1980, the production dropped from 104 00 tonnes to 50 00 tonnes. Conservation programs have now been developed to help conserve the ‘castania-rich’ forests, by developing a management system and promoting governmental support, and by facilitating the sharing of Brazil nut and forest knowledge across the borders of Peru, Bolivia and Brazil. It is reported that to justify forest protection, nut marketing has to benefit local communities.
Further reading Amazon Conservation Association website, ‘Conserving Castanales’ and ‘More than just nuts’: http://www.amazonconservation.org Clay, J. W., and Clement C. R. (1993). Selected species and strategies to enhance income generation from amazonian forests. FAO working papers 93/6. (Food and Agriculture Organisation of the United Nations: Rome.) Mori, S. A. (1992). ‘The Brazil Nut Industry – Past Present and Future.’ (Island Press: Washington.) Mori, S. A., and Prance, G. T. (1990). Taxonomy, ecology and economic botany of the Brazil Nut, Advances in Economic Botany 8: 130–150. Rosengarten, Jr., F. (1984). ‘The book of edible nuts.’ (Walker and Company: New York, USA.) Wickens, G. E. (1995). ‘Edible Nuts.’ Non-Wood Forest Products 5. (Food and Agriculture Organisation of the United Nations: Rome.)
Bunya nuts The Bunya Pine or Bunya Bunya tree, Araucaria bidwillii, grows to an enormous tree reaching 40 m in height. It is often seen growing in large old gardens or public parks. Bunya Pine belongs to the Araucariaceae family and is native to rainforests in Queensland. Named after the Bunya mountains north-west of Brisbane, the range of Bunya pines extends to northern Queensland. In cultivation the tree grows well along southern coast of Australia where it tolerates frost. The conical canopy forms a rounded crown when trees mature and the branches radiate out from the straight rough-barked trunk. Leaves are small and glossy, tough and very spiky and arranged in spiral formation around the branches. Bunya pines produce both male and female cones on the same tree. The male cones are small and cylindrical and the female cones that contain the large edible nuts, are egg-shaped and up to 30 cm in length and 10 kg in weight. The female cones drop from the tree when mature. They are composed of large woody scales each bearing a single flattened seed. The seeds are pointed and range between 25 mm and 50 mm in length. They have a milky edible flesh. Female cones are produced approximately every three years.
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Indigenous Australians valued the nutritious seeds and headed for known sites such as the Bunya Mountains to gather the nuts. The nuts were eaten raw, roasted or pounded into flour to make a kind of bread. While the Bunya pine is not cultivated for nuts, the cones are gathered from the wild and the nuts are marketed at niche Bush Tucker markets.
Bunya pine.
Further reading Bush Tucker Plants website http://www.teachers.ash.org.au/bushtucker/bunya_nut Cronin, L. (1988). ‘Key Guide to Australian Trees.’ (Reed Books Pty Ltd: Melbourne.)
Malabar chestnuts
Malabar chestnut foliage, flowers and fruit.
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This tree has numerous common names including Guiana chestnut, Shaving Brush Tree, Provision Tree and Saba nut. The botanical name is Pachira aquatica and it belongs to the Boabacaceae family along with the Baobob and Durian. Malabar chestnuts are native to southern Mexico and northern Brazil where they inhabit tropical estuaries. However, the tree grows well in cooler climates and in Australia it has been cultivated in mild inland and coastal areas of Queensland. It will tolerate brief exposure to low temperatures but not frost. The tree is a fast-growing evergreen tree and in moist tropical conditions it reaches
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20 m in forests but size is much reduced when conditions are not as favourable. Handsome glossy palmate leaves form a dense canopy making it an attractive specimen tree. The tree is also cultivated as an indoor pot plant. Malabar chestnut flowers are large, white, fragrant and self-fertile displaying a tassel of long cream showy stamens. The fruit that forms develops into a pear-sized woody green pod that ripens to brown and opens to reveal five valves. The capsules burst open when the seeds are ripe and the tightly packed seeds (nuts) inside fall to the ground. The nuts are round in shape, about the size of a hazelnut and can be eaten raw or roasted. When raw they taste like peanuts and when roasted they have the flavour of chestnuts, The young leaves can also be eaten as a cooked vegetable.
Further reading California Rare Fruit Growers Inc. (1996). ‘Malabar Chestnut Fruit Facts’: website http://www.crfg.org Daleys Fruit Newsletter (2003): website http://www.dayleysfruit.com.au Tradewinds Fruit. ‘Malabar Chestnut’: website http://www.tradewindsfruit.com
Pine nuts There are twelve species that produce edible pine nuts but the best known is Pinus pinea, commonly called the Stone Pine or Umbrella Pine. Most pine nuts available in shops are harvested from the Korean pine (P. koraensis). Pine nuts from this species are produced in large quantities in China. Another species to be harvested for its pine nuts is P. edulis known as ‘pinyon’, or by its Spanish name, ‘piñon’. This species is grown on the Colorado plateau and in New Mexico and Arizona. Italy is the largest producer of pine nuts from Stone pine trees followed by Spain and Portugal. In these countries the tree is also used for timber, as shelter belts, for erosion control and for resin. The trees are also attractive landscape trees along the Mediterranean coast. Stone pines are propagated by sowing fresh seed in a seed sowing medium kept at a temperature between 17–19°C. °C. C. It is suggested that the addition of mycorrhizal fungus gathered from beneath other pine trees will improve growth. When established, young stone pine Stone pine. seedling should not be over-
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watered and care is required when re-potting or planting out to avoid damage to the tap root. Stone pine trees tolerate periods of dryness, they are frost tolerant and they prefer a sandy soil. When planting young trees, a tree spacing of 10 m has been suggested for nut producing trees and 5 m for trees for a wind break planting. In Portugal one tree density suggested is 625 grafted trees per hectare initially, with some tree removal after 12, 22 and 32 years until reaching a final density of some 100 trees per hectare. Alkaline soils and wet soils should be avoided when planting stone pines. Aleppo pine is reported to have shown some tolerance to alkaline soils in Spain. When established, Stone pine trees can be pruned to remove low branches to allow machinery access and prevent damage from grazing animals. In New Zealand, Stone pine trees may produce cones from about year six depending on the growing conditions. At one planting in New Zealand, trees produced their first cones after 3½ years. In Spain grafted trees do not produce flowers during the first years and it is reported that it is 4–5 years before the first ripe cones are ready to harvest. During the first 15–20 years grafted stone pines produce only female flowers and catkins are not produced until after this. Thus grafted trees less than 15 years need to be artificially pollinated or planted next to mature stands that produce large amounts of pollen. The total number of cones produced varies from tree to tree. Large individual trees in Spain have been known to produce over 1000 cones per year. A genetic improvement program in Spain aims to find and select stone pines that are considered to be good cone producers and to propagate them vegetatively. Work in Italy to improve yield and nut quality has also been underway. Here trees have been propagated by grafting onto rootstock seedlings that are at least two years old. Among the various rootstock species used in Italy is P. radiata and the preferred graft is a cleft graft done in summer. Side grafting is also practised. In Spain the species P. halepensis has been used as a rootstock in grafting trials. A new grafting technique introduced in Spain is needle grafting, in which a pair of leaves is grafted with their corresponding patch. The cones of stone pines usually take three years from pollination to ripening. Traditionally people harvesting the nuts climb the trees and use long poles to knock down the cones. It has been reported that in Europe the annual yield of nuts is approximately 500 kg/ha. Each cone contains about 50 nuts and 100 kg of cones holds about 20 kg of nuts. Stone pine trees can be found in many parks and gardens in Australia but no information has been located on commercial production of pine nuts in this country. A small plantation that has potential for pine nut production is located north of Perth in Western Australia.
Further reading Australian National University School of Resources, Environment and Society, ‘Pine nuts’: website http://www.sres.anu.edu.au Australian New Crops website http://www.newcrops.uq.edu.au
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Catalan, G. S. (1998). Current situation and prospects of the stone pine as a nut producer. Nucis Newsletter No. 7. Information Bulletin of the Research Network on Nuts (Food and Agriculture Organisation of United Nations, Centre international de Hautes Etudes Agronomiques Méditerranéennes (FAO-CIHEAM): Reus Spain.) FAO-CIHEAM. (1995). ‘Stone pine: A new established sub-network within the FAO inter-regional cooperative research network on nuts’. Nucis Newsletter No. 4. Review of Congresses and Meetings. FAO-CIHEAM. (1999). ‘Stone pine needle grafting’. Nucis Newsletter No. 8. Review of Congresses and Meetings. Franconi, M. (2000). Opportunity for a Stone Pine venture. Quandong, West Australian Nut and Tree Crop Association 26(4), 30. Trap, L. ‘Pinus pinea – An edible nut pine of many uses. Australian New Crops Newsletter, Queensland. Available at http://www.newcrops.uq.edu.au/newslett/ncn16153.htm
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Appendix
1
Nut tree notes for gardeners
Nut trees have great beauty and they come in all shapes and sizes. Macadamia, pistachio, hazelnut or almond are ideal smallish trees for suburban gardens, while cashew, chestnut, walnut and pecan trees make excellent shade trees for larger parks and gardens. And the bonus is freshly harvested nuts that are the sweetest nuts you will ever taste. Just as in a commercial situation, the type of nut tree to plant in a garden will depend upon the climate, soil type, aspect, and water availability as well as the space available. Almonds, chestnuts, hazelnuts, macadamias, pecans, pistachios and walnuts will all grow in temperate gardens in Australia but in southern regions pecans are unlikely to produce mature fruit due to the lack of a sufficient number of hot days. All nut trees grow best with frequent watering in dry seasons. The most dry tolerant nut tree is pistachio, followed by hazelnut. Pecans and macadamias are best suited to sub-tropical and northern inland regions and cashew trees grow in the tropics. At harvest, nuts are more akin to a fruit than a nut and all nuts except chestnuts and fresh pistachios must be dried immediately or they will go mouldy. Chestnuts and fresh pistachios are stored in the refrigerator immediately after harvest. The following is a summary of different nut trees to grow in the garden. More information is included in the specific nut chapters.
Almond Almond trees are smallish deciduous trees that grow to about four metres in height in cultivation and tolerate heat and cold, but humidity can cause disease problems. They are one of the first garden trees to flower in late winter. Like their peach relations, almond trees are pollinated by insects and require cross-pollination to produce nuts; that is, two varieties of almond are needed. There are self-pollinating varieties available (e.g. All-inone) and single self-pollinating trees are an ideal choice for the home garden.
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Almond blossom falls to the ground in early spring forming a carpet of white petals. When the flower is fertilised, a pointed furry fruit develops and swells through summer and matures in early autumn. The velvet-covered hull splits open revealing the nut. At this stage the branches are shaken and the nuts and hulls fall to the ground. The nuts are removed from the hulls and dried before storage. Almond trees are often grown in the garden purely for their pretty blossom, shade, and yellow autumn colour because, more often than not, parrots and cockatoos devour the crop of nuts before they are ready to harvest.
Cashew In tropical gardens cashew trees are easy to grow and provide welcome shade. They are evergreen with large leathery leaves similar to pistachio to which they are related. Different varieties of cashew develop different shaped canopies. The flowers form in clusters and there are three types of flowers on each tree: males, females and hermaphrodite flowers. Cashew trees are insect pollinated and require little maintenance apart from watering in dry weather, especially when trees are young. The trees grow quickly in favourable conditions and fruit is produced about three or four years after planting. The cashew nut forms at the bottom of a fleshy stalk called the cashew apple and the fruits fall to the ground over a three month period. While the cashew apple is useful for making juices and desserts, the cashew nut is troublesome to extract due to the extremely caustic liquid in the shell. Great care should be taken to avoid skin contact with this liquid.
Chestnut Chestnut trees are shady deciduous trees reaching more than five metres in height under favourable conditions. The leaves are large and deep green and both male and female flowers form on the one tree. In spring, after the first leaves emerge, slender sprays of tiny male and female flowers appear. Chestnut flowers are pollinated by wind and for a good crop of nuts, it is best to grow at least two different varieties of chestnut. After the female flowers are fertilised, the prickly fruits swell to almost tennis ball size through summer and by autumn they start to yellow and split open revealing one or more glossy chestnuts. The thorny burrs and shiny brown nuts fall to the ground and the chestnuts are extracted from the burrs using garden gloves or by rolling the burr under a boot. Some nuts fall free of the burr. As soon as they are harvested, the nuts are stored in a plastic bag in a cool-room or refrigerator. Chestnuts are generally used fresh and can be roasted (pierce the skin first) as a hot snack or cooked and peeled for soups, stir fries, salads and desserts. Chestnut trees tolerate heat and cold and make wonderful shade trees. They are relatively easy to grow and less fussy about soil than walnuts and pecans. Chestnuts are free from pests and diseases with the exception of birds that may devour the nuts in some regions, root-rot that can cause tree dieback, and in some varieties, nut-rot can occur during a wet harvest.
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Hazelnut Hazelnut trees are deciduous and may grow to four metres in favourable conditions. The trees produce sucker growth that forms a thicket of trunks unless the suckers are removed, consequently they can be grown as a hedge. Tiny red female flowers form on bare branches in winter followed by bunches of pencil-thick catkins in spring. The branches tend to be upright and the leaves are finely serrated and heart-shaped. Hazelnuts are wind pollinated and small clusters of nuts develop in summer and mature in autumn. When the husk around the nut starts to yellow, it falls to the ground. Some varieties bear nuts that fall free of the husk and others have to be removed from the husk. Hazelnuts must be cross-pollinated to produce nuts and a crop is not reliable unless a few compatible varieties are planted. Very often the trees appear to have a crop but the nuts may not be fertilised and they will be empty. Hazelnuts are dried as soon as they are harvested and stored in a dry vermin-proof place. Hazelnut trees are easy to grow and suffer few pests and diseases but crops can be decimated before harvest by cockatoos and parrots.
Macadamia Macadamia trees are easy to grow evergreen trees reaching four metres in temperate gardens but exceeding five metres in subtropical conditions. They are native to rainforests of northern New South Wales and southern Queensland but they will grow and fruit in temperate regions if frost protection is provided when the trees are young. The leaves are tough and serrated and the small white flowers that form in drooping candles bloom over a long period. Macadamia belongs to the Proteaceae family and the flowers are very like those of Grevillea. The dense, leafy, rounded canopy makes an excellent garden tree or large hedge. There are two macadamia species, both of which produce nuts when only one tree is planted. Macadamia integrifolia has smaller leaves and is slightly less vigorous than Macadamia tetraphylla that forms a larger tree in southern regions. Macadamia flowers are insect pollinated and after fertilisation round, green fruit form in pendulous bunches. The crop matures from autumn through winter to spring when the leathery husks split open and the nuts fall to the ground. Most nuts fall in their husks and due to the thick shell, birds are seldom a problem. Rats, however, can be a big problem. Macadamia nuts are taken out of the husks and dried before storage. The most difficult part about growing macadamia nuts is cracking the nut to extract the kernel!
Pecan Pecan trees are tall deciduous trees that love cold winters, long hot summers and summer moisture. They are relatively easy to grow and not prone to disease in Australia. Pecans belong to the same botanical family as the walnut but they are less fussy about soil than walnuts. Different varieties of pecans form different shaped trees. Some are pyramidal while others form spreading trees and choice of tree shape may determine the variety planted in the garden.
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In spring, catkins emerge closely followed by small female flowers and the leaves. Pecans are wind pollinated and while a single tree will produce some nuts, to obtain a good crop, two varieties are needed for cross-pollination. The fertilised fruit form in bunches and swell over the summer months. The outer husk or shuck splits open in late autumn and the nut falls to the ground. Unfortunately crows and cockatoos can devour the nuts before they mature. Pecans are dried as soon as they are harvested. The shell is strong but thin and the nut is tightly enclosed. Pecan trees turn a colourful soft yellow before the leaves fall in late autumn.
Pistachio Pistachio trees are slow-growing smallish deciduous trees reaching three to four metres in favourable conditions. They tolerate heat and cold, and while they survive periods of drought, summer moisture is essential for a good crop of nuts. Pistachio branches tend to be spreading and leaves are rounded, leathery and sparse. The trees are not susceptible to many pests and diseases in Australia although a type of canker that causes dieback can result in tree death, and cockatoos may attack the nuts before they mature. Pistachios are either male or female and one male tree is sufficient to pollinate about ten female trees. In spring tiny flowers emerge with the leaves. Pistachio trees are wind pollinated and after they are pollinated, the female flowers form bunches of small fruit through summer. In autumn, the fruit turns pink and the nuts mature. The branch of nuts can be shaken so that the nuts fall onto a ground sheet. If left too long on the tree after maturity, the nuts fall on the ground and are tedious to harvest because of their small size. Because the shell of a pistachio nut splits open as it matures, dirt and disease may enter the nut if it falls on the ground. The hull encasing the nut is removed from the nut immediately after harvest to prevent staining of the shell and the nuts are then dried before storage. The leaves colour before falling in late autumn.
Walnut Walnut trees are large deciduous trees and when mature they create wonderful shade if grown in favourable conditions. They require a cold winter and warm summer but most of all they require very well-drained soil that is kept moist through summer. Different walnut varieties form different tree shapes and while some varieties are almost pyramidal, other varieties are wide with weeping branches. Walnut leaves are large and tender and both male and female flowers form on the same tree. While it is possible to harvest nuts from a single tree, two varieties that flower at a similar time are required for good crops. In spring, large catkins emerge along with the leaves and tiny female flowers. Walnuts are wind pollinated and after fertilisation, the nuts swell to form green egg-sized fruit through summer. In autumn, the hull splits open and the nut falls to the ground. To avoid deterioration, the nuts are quickly harvested and dried before storage. Walnut trees turn a lovely soft yellow in autumn.
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The one troublesome walnut disease in Australia is walnut blight, a bacterial disease that turns the nuts black inside. Walnut blight is controlled with a copper-based fungicide but large trees would be difficult to spray in a garden situation. Cockatoos and some parrots can devour walnuts before the crop matures.
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Index
acidification 46 aflatoxin 184 almond 81, 219 cultivars 86 flowering 84 markets 97 processing 96 Almond Board of Australia 82 alternate bearing 84, 167, 171, 172, 176, 183, 185, 187,212 Anacardium occidentale 100 Araucaria bidwillii 213 Australian Macadamia Society 141 Australian Pecan Growers Association Inc. 157 Australian Walnut Industry Association Inc. 190 beneficial insects 53, 68 Bertholletia excelsa 211 biennial bearing see alternate bearing biological control 53, 68, 169 bird control 19, 54, 91 bird damage 54, 84, 91, 119, 136, 168, 183, 201 blank nuts 138, 178, 184, 206 bopple nuts 141
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Bordeaux 202 Brazil nuts 211 bud wood 23 budding 22 Bunya pine 213 canopy management 47, 49 Carya illinoensis 158 cash flow 79 cashew 99, 220 cultivars 103 flowering 100 marketing 107 yield 106 Castanea spp. 109 chestnut 109, 220 blight 110, 119 cultivars 114 flowering 112 grading 122 marketing 122 processing 123 storage 122 Chestnut Growers of Australia Ltd. 109 chilling requirements 15, 83, 111, 127, 159, 177, 192 climate 15, 63
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cobnuts 125 compatibility 85, 128, 145 compost 66 copper resistance 202 Corylus spp. 125 cross pollination 84, 112, 128, 144, 160, 194, 219, 221, 222 crotch 48 crown gall 36, 57, 88, 92, 116, 165, 169 cuttings 27, 132 dichogamy 193 diseases, general 53, 56, 63, 68 almond 92 cashew 106 chestnuts 119 hazelnut 137 macadamia 151 pecan 169 pistachio 183 walnut 201 drainage 30 drip irrigation 33, 42, 44, 89 drying nuts 77, 138, 153, 171, 186, 206 dust 68 economics 62, 72, 73 Ethephon 153, 204 fertigation 46, 47, 89 fertilisers 39, 44, 45, 66, 89, 134, 148, 149, 167, 182, 199 filberts 125 fresh nuts 77, 120, 185, 186 frost 15, 19, 63, 83, 111, 127, 143, 159, 191 garden trees 219 grafting 24 ground covers 40, 50, 65, 150 harvesting 57, 68, 77, 94, 106, 120, 137, 152, 170, 184, 203 hazelnut 125, 221 cultivars 129 flowering 127
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grading 139 marketing 139 Hazelnut Growers of Australia Ltd. 126 health benefits 1 hedging 49, 50, 91, 149, 200 herbicides 39, 51, 52, 133, 148, 198 hermaphrodite flowers 100, 220 humidity 16, 43, 63, 68, 83, 111, 143, 159, 177, 192 insect pollination 82, 84, 142, 144, 220, 219 insurance 75 Integrated Pest Management 53, 150 irrigation 18, 32, 40, 57, 116, 134, 148, 166, 181, 199 Juglans spp. 189 Kindal Kindal 141 landform 19 lateral bearing 194 layering 25, 132 leaf analysis 45, 89, 117, 135, 148, 167, 182, 200 lichen 168 lifestyle 62, 72 limb bending 47 livestock 40, 52, 56, 66 living off-farm 20 location 19, 64, 84, 101, 112, 127, 143, 159, 177, 192 macadamia 141, 221 cultivars 145 flowering 143 marketing 155 processing 154 Macadamia spp. 142 machinery 19, 20, 76, 77, 79 Malabar chestnuts 214 manure 149 markets 69, 71 marron 110
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I n d ex
micro-propagation 27 mother trees 22, 147 mowing 43, 51, 52, 64, 65 mulching 30, 198 neck buds 23, 49, 199 non-splits 178, 186, 187 nut allergy 2 nut producing areas 12, 13 nut production 9, 10 nut rot 113, 119 nut shells 172 nutrient deficiency 44 nutritional analysis of nuts 4, 5 Nuts for Life 1, 2 orchard floor management 50, 57 layout 31,64, 85, 103, 144, 161 size 77 organic certification 62, 69, 72 farming 61 fertilisers 47 matter 30 over-capitalisation 77, 79 Pachira aquatica 214 peanuts 1 pecan 157, 221 cultivars 160, 163 flowering 160 grading 171 marketing 172 processing 172 production 157 pests, general 53, 56, 64, 68 almond 91 cashew 105 chestnuts 118, 119 hazelnut 136 macadamia 150 pecan 167 pistachio 183 walnut 201
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pH 17, 30, 46, 63, 83, 101, 111, 127, 143, 158, 177, 191 Phomopsis sp. 119 Phytophthora spp. 57, 119, 151, 184, 197, 203 pine nuts 215 Pinus spp. 215 pistachio 175, 222 cultivars 179 flowering 178 grading 186 marketing 187 processing 185 production 175 Pistachio Growers Association Inc. 176 Pistacia spp. 175 planting techniques 36, 88, 104, 133, 147, 165, 180, 198 pollination 84, 101127, 143, 160, 178, 192 pollinisers 85, 113, 114, 127, 128, 160, 161, 179 processing facilities 20, 69 propagation 21, 87, 103, 115, 132, 146, 165, 180, 197 protandrous 160, 193 protogynous 160, 193 pruning 48, 91, 117, 135, 149, 167, 182, 200 Prunus spp. 82, 87 pulsing 41, 42, 44 Queensland nut 141 rainfall 16, 63 rats 151 root rot 19, 30, 34, 57, 119, 151, 183, 196, 203 rootstocks 21, 87, 115, 132, 146, 165, 179, 196 salinity level 17, 18, 83, 104, 143, 167, 181, 192, scion wood 24 self-fertile 160 self-sterile 126
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shading 51 shuck 161, 170 skirting 149 soil analysis 29, 46, 63, 66 modification 30 moisture 34, 40, 47, 89 moisture sensors 35, 40, 42 type 17, 29, 46, 63, 143 spray equipment 56, 77 sprinkler irrigation 33, 42, 89 stone pine 215 stratification of seed 88, 180 suckers 26, 126, 132, 133 sunburn 37, 133, 148, 191 taxation 73, 74 temperature requirements 15, 63, 127, 159, 143, 191 tensiometers 35, 40 terminal bearing 194 top-working 25, 115, 198 tree age 50 guards 37, 88
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nutrition 44, 66 spacing 31, 79, 113, 129, 144, 162, 194 training 47, 48, 89, 104, 118, 133, umbrella pine 215 varietal selection 64 walnut cultivars 194 flowering 192 grading 206 marketing 207 production 189 water requirement 18, 40, 63, 84, 89, 101, 111, 127, 143, 159, 177, 192 weed control 30, 39, 43, 51, 64, 65, 89, 116, 133, 135, 198 wind 16, 37, 49, 64, 84, 111, 127, 159, 177, 192 pollination 110, 112, 126, 160, 176, 191, 220, 221, 222 windbreaks 31, 64, 88, 147 xenia 112
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