Abstract
Thinning is a critical but challenging practice in apple production, especially for organic producers. The objective of this experiment was to determine if exclusion netting, used to manage insect pests and stress, could reduce fruit set and thinning requirements of ‘Gala’ and ‘Honeycrisp’ apple trees in Michigan and Washington, U.S.A., respectively. Nets were closed around whole canopies at different timings based on a predetermined percentage of open flowers. In 2017 and 2018, netted trees set a full commercial crop regardless of percentage of open bloom at the time of netting, including prebloom enclosures. Fruit set and yield of netted ‘Honeycrisp’ trees were significantly lower than non-netted, nonthinned controls but similar to non-netted hand-thinned controls. ‘Gala’ fruit set and yield did not differ among treatments. Exclusion netting markedly reduced the number of mature seeds and increased the number of nonfertilized seeds in both cultivars. Pollinator exclusion to ‘Gala’ in a frost year increased parthenocarpic fruit set two-fold compared to non-netted trees. Fruit size, shape, and quality attributes of ‘Gala’ were were similar among treatments, but ‘Honeycrisp’ fruit were significantly smaller than hand-thinned, non-netted controls. Netting may constitute an alternative, viable strategy to manage fruit set but requires testing on different cultivars.
Highlights
IntroductionGlobal organic fruit production increased 109% between 2008 and 2013 (on a land area basis) with Malus x domestica Borkh
Global organic fruit production increased 109% between 2008 and 2013 with Malus x domestica Borkh. and Musa acuminate L. showing the largest gains [1].Developing novel, crop load management methods for organic apple systems will improve producer profitability while meeting increasing consumer demand for organically produced fruit
Mechanical thinning has been applied to different apple varieties with varying levels of success [5,6] but this practice may increase the risk of fire blight infection [7]
Summary
Global organic fruit production increased 109% between 2008 and 2013 (on a land area basis) with Malus x domestica Borkh. Developing novel, crop load management methods for organic apple systems will improve producer profitability while meeting increasing consumer demand for organically produced fruit. Flower and fruit thinning are essential field practices for sustainable tree fruit production. Hand thinning is the most accurate method to reduce crop load but is no longer practical due to labor shortages, cost, and time. Mechanical thinning has been applied to different apple varieties with varying levels of success [5,6] but this practice may increase the risk of fire blight infection [7]
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