2019 ASHS Annual Conference

Organic apple production is growing worldwide, and Washington State (WA), as the leading apple producer in the U.S., accounts for approximately 90% of domestic certified organic apples. The main varieties cultivated as organic are Gala and Fuji followed by Golden Delicious, Red Delicious, Granny Smith, Cripps Pink, Braeburn, Honeycrisp™ and other new varieties. The use of overhead nets in the orchards to reduce hail damage is becoming increasingly widespread as protection against other stressors like birds, sunburn and pests. All these factors are important in traditional orchard and are even more relevant in organic production due to the restriction in using synthetic compounds. The use of orchard nets can impact tree physiology altering microclimate and light, vegetative growth, water use and photosynthesis. Moreover, fruit quality is strongly influenced especially in terms of color, physiological disorders and dry matter accumulation. Thinning is one of the most critical issues in apple organic production where few products can be utilized. Thinning strategies in organic production are limited to hand thinning (challenging to apply on large acreage at early fruitlets stage), lime sulfur, other vegetable oil emulsions and mechanical thinning. Less than 20% of fertilized flowers are necessary to guarantee a consistent annual crop. If the full bloom could be avoided, the thinning effort and cost associated with it would be reduced, in particular for Honeycrisp^TM, a variety that usually sets all fertilized flowers into fruit. The idea to utilize a completely closed drape net system around each orchard row, known in Europe as Alt Carpo’ (to exclude Cydia pomonella), was tested on organic Honeycrisp^TM in WA to exclude bees at different time points throughout bloom. The percentage of king flowers opened to total flower buds available was used as a guideline for deciding when to isolated trees using the drape net system to reduce the pollination (bee exclusion). Different percentages of bloom were tested against three control treatments: one in which trees were closed inside nets before bloom, one without netting (unthinned), and one without netting (normal thinning for commercial Honeycrisp^TM orchards) until harvest. Fruit set, yield, number of viable and non-fertilized seeds per apple and instrumental fruit quality parameters were assessed to determine if netting can play an effective role in organic thinning as a physical barrier for pollinators.