S16 - Session O2 - Multi-year evaluation of insect exclusion netting on apple fruit set and the carry-over effect on seed formation, fruit size and fruit shape

Authors: Mokhles ELsysy *, Todd Einhorn

Thinning is a critical but challenging practice in apple production, especially for organic producers. Netting of tree canopies, used to manage insect pests, hail and abiotic stress, could potentially produce target crop loads and eliminate or mitigate thinning, depending on the percentage of open bloom accessible to pollinators at the time of canopy enclosure. The objective of this multi-year project was to determine the influence of net enclosure on fruit set, seed formation, and fruit quality. Whole canopies were enclosed at different bloom stages: 0% (pink, pre-bloom), 20%, 40% and 80% open king bloom. Over the course of five years experiments were conducted with 'Fuji', 'Honeycrisp', 'Gala, and 'SweeTango'. The effect of seed number and quality (Mature, Non-developed, non-fertilized) was assessed on fruit weight and fruit shape (evaluated in the lateral and longitudinal planes). Relationships were examined between relative distribution or quality on cortical tissue volume. Moreover, seed characteristics were assessed for fruit that had naturally abscised versus those that were retained. Fruit set and crop load was positively related to the percentage of open bloom at net timing, but the relationship varied according to cultivar. Fuji and Gala were capable of setting target crop load when netted at pink. Netting affected seed formation but had minimum effects on fruit quality. The relationship between seed number and fruit size was not significant; however, when fruit were categorized on their seed content, the highest category of seed content produced fruit of greater fruit size and uniform shape. Naturally abscised fruit had lower seed content compared to hand thinned fruit that would have otherwise set. Pollen sources of fruit netted at 0% king (pre-bloom netting) are currently being explored.