Sun Protection Manual for Fruit
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Sun Protection for Fruit A practical manual for preventing sunburn on fruit - 2011 Compiled and edited by: Sam Lolicato, Department of Primary industries, Tatura, Victoria Reviewers: Dr Larry Schrader, Washington State University, Tree Fruit Research and Extension Centre Dr Bob Evans, United States Department of Agriculture, Agricultural Research Service Dr Ian Goodwin, If you would like to receive this information/publication in an accessible format (such as large print or audio) please call Department of Primary Industries, Tatura, the Customer Service Centre on 136 186, TTY 1800 122 969, Victoria or email [email protected]. Pam Strange, Published by the Department of Primary Industries Farm Services Victoria Division, June 2011. Department of Primary Industries, Irymple, © The State of Victoria 2006 Victoria This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968. Graeme Thomson, This publication is copyright. Reproduction and the making available of this Department of Primary Industries, Knoxfield, material for personal, in-house or non-commercial purposes is authorised, on condition that: Victoria • .the copyright owner is acknowledged Dr Simon Middleton, • .no official connection is claimed Agri-Science Queensland • .the material is made available without charge or at cost • .the material is not subject to inaccurate, misleading or derogatory Henry Schneider, treatment. Ethnic council c/o - Department of Primary Requests for permission to reproduce or communicate this material in any way not permitted by this licence (or by the fair dealing provisions of the Copyright Industries, Tatura, Victoria Act 1968) should be directed to the Customer Service Centre, 136 186 or email [email protected]. Olive Montecillo, Authorised by the Department of Primary Industries Department of Primary Industries, Echuca, 1 Spring Street, Melbourne 3000. Victoria ISBN: 978-1-74264-749-4 (print) ISBN: 978-1-74264-750-0 (online) Disclaimer The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. For more information about DPI go to www.dpi.vic.gov.au or phone the Customer Service Centre on 136 186. 2 Sun protection for fruit - A practical manual for preventing sunburn on fruit - 2011 Sun Protection For Fruit A practical manual for preventing sunburn on fruit - 2011 Compiled and edited by: Sam Lolicato, Department of Primary industries, Tatura, Victoria Reviewers: Technical Working Group: Dr Larry Schrader, Sam Lolicato, Department of Primary Washington State University, Tree Fruit Research Industries, Tatura, Victoria and Extension Centre Dr Ian Goodwin, Department of Primary Industries, Tatura, Victoria Dr Bob Evans, Chris Peters, Fruit Growers Victoria Ltd United States Department of Agriculture, Richard Hawkes, Apple & Pear Australia Ltd Agricultural Research Service Michael Crisera, Fruit Growers Victoria Ltd Dr Ian Goodwin, Department of Primary Industries, Tatura, Victoria Pam Strange, Department of Primary Industries, Irymple, Victoria Graeme Thomson, Department of Primary Industries, Knoxfield, Victoria Dr Simon Middleton, Agri-Science Queensland Henry Schneider, Ethnic council c/o - Department of Primary Industries, Tatura, Victoria Olive Montecillo, Department of Primary Industries, Echuca, Victoria Sun protection for fruit - A practical manual for preventing sunburn on fruit - 2011 3 Three types of sunburn on apples 4 Sun protection for fruit - A practical manual for preventing sunburn on fruit - 2011 Contents Introduction 6 What causes sunburn of fruit? 7 Types of sunburn on apples 7 How to assess sunburn risk 8 Sun protection options 12 1. Best Management Practices 13 2. Spray-on sun protection products 15 What are spray-on sun protection products? 15 How do they work? 15 Types of spray-on sun protection products 15 Advantages 17 Disadvantages 17 Economics 17 3. Shade netting 19 What is shade netting? 19 How does it work? 19 Types of shade netting 20 Advantages 22 Disadvantages 22 Economics 22 4. Over-tree sprinkler cooling systems 23 What are over-tree sprinkler cooling systems? 23 How do they work? 23 Types of over-tree sprinkler cooling systems 23 Advantages 26 Disadvantages 26 Economics 27 Overview 28 References 29 Appendix 1 - Case studies 30 Appendix 2 – Estimating the pay-back period for shade netting and over-tree sprinkler cooling 39 Sun protection for fruit - A practical manual for preventing sunburn on fruit - 2011 5 Introduction Many fruit trees in northern Victoria are growing close to the The manual relies heavily on information on apples, but upper boundary of their ideal environment for temperature where possible information about pears and other fruit is and sunlight. For example, apple production in northern included. Victoria increased significantly in the 1990s after the Also, the manual focuses mainly on sunburn in fruit, which is development of apple varieties with high market acceptance the obvious visible symptom of an excessively warm climate. and higher heat tolerance. Even with varieties more tolerant During the hottest part of the day, when air temperatures of heat, it is common for the local industry to experience rise above 30 to 35ºC, fruit tree photosynthesis is likely some level of sunburn on fruit, causing lower-value and to slow, causing general heat stress, which will reduce more variable pack-outs. Plants growing in an environment potential fruit yield. This manual will not deal with this in with ambient temperatures close to the limit of what they detail, but we can expect that sunburn control options will can tolerate will be the first to show definite adverse also have some general yield benefits due to reductions in symptoms caused by predicted climate change. general heat stress on trees. Some modern fruit production techniques can increase the risk of sunburn. The most obvious example is the use of fruit trees with dwarfing rootstocks growing on trellis and using training systems that allows direct sunlight to penetrate throughout the tree’s canopy. This can increase fruit yields and improve colour development but can increase the risk of sunburn. Orchardists estimate fruit production losses due to sunburn in the Goulburn Valley in northern Victoria vary from 6 to Early sunburn on young Sundowner apples 30 per cent, depending on seasons and the type of fruit. (early December 2010) Estimates of recent losses in susceptible orchards without sun protection vary from 10 to 40 per cent in Granny Smith apples, 15 to more than 50 per cent in Gala apples, 10 to 25 per cent in Pink Lady apples and 10 to 15 per cent in Williams pears. Orchardists in northern Victoria have developed many techniques and infrastructure upgrades to reduce economic losses due to sunburn. Some control measures work better than others and the results are often variable. Some of the variable results are due to difficulties in applying suitable Sunburn on Sundowner apples (early April 2011) orchard management practices and techniques. The objectives of this manual are to: 1. Outline the causes of sunburn in fruit; 2. Summarise the different techniques and infrastructure upgrades used by orchardists to reduce sunburn in fruit in Victoria, Australia and the world; and 3. Assess advantages and disadvantages of the main sun protection techniques, including estimates of their Sundowner apples 3 days after a 40ºC day in economic consequences. December 2010 6 Sun protection for fruit - A practical manual for preventing sunburn on fruit - 2011 What causes sunburn of fruit? Types of sunburn on apples The energy of sunlight can cause damage to the sun-exposed 1. Sunburn necrosis surface layers of fruit. This is caused by heat, when the fruit surface temperature of Sunburn is more due to the radiative force of the sun than air an apple reaches 52 ± 1ºC for 10 minutes. Cells die and later temperature. a sunken dark brown or black (necrotic) patch may appear. The maximum temperature of the sun-exposed fruit Types of apple sunburn (from left to right): surface of apples is often 10 to 18ºC higher than the 1. Sunburn necrosis 2. Sunburn browning maximum shaded air temperature (Schrader et al. 2003a). 3. Photo-oxidative sunburn (or bleaching) The temperature of a fruit’s surface in direct sunlight will always be higher than the officially reported air temperature at the same location. The Bureau of Meteorology normally reports temperatures from thermometers positioned inside shaded or ‘screened’ boxes. Also, unlike leaves, many types of fruit (e.g. apples and pears) have very limited cooling (Picture from Larry Schrader) capacity via transpiration from the skin of the fruit. 2. Sunburn browning As a general guide, sunburn of apples can occur when shaded air temperatures are above 30ºC and fruit surface This is the most common type of sunburn and results in a temperatures are above 45ºC. yellow, brown or dark tan patch on the sun-exposed side of the apple, usually a few days after the initial damage Sometimes sunburn will not be obvious until after a period was done. Cells do not die and damage initially appears of cool storage. Heat stress on fruit can also increase the superficial, although deeper apple flesh will show more incidence of other skin disorders in apples (e.g. Lenticel change in cool storage. This damage occurs when the fruit Marking, Bitterpit, Splitting and Watercore; Schrader et al. surface temperature reaches a specific point while exposed 2003b). to direct sunlight. The minimum threshold fruit surface Like human skin, apple fruit skin can become acclimatised temperature that will cause sunburn browning varies from to sun and heat.