Enclosure of apple canopies with insect exclusion, anti-hail nets during early bloom stages reduces fruit set and seed content of ‘Honeycrisp’, ‘SweeTango’ and ‘Fuji’ but does not negatively affect fruit size

Thinning is a challenging practice in organic apple production. We previously demonstrated the use of insect exclusion netting to reduce fruit set and thinning when applied at different stages of bloom; however, fruit set of different cultivars responded differently to bee exclusion with nets. The objective of the current experiment was to evaluate the technique on the apple cultivars 'Honeycrisp', 'Fuji' and 'SweeTango' in a northern production climate (Michigan, USA). In two consecutive years (2019 and 2020), whole canopies were enclosed with nets at different percentages of open flowers from 0% bloom [i.e., pink stage] to 80% king bloom (KB). Fruit set of netted canopies was positively related to percentage of open KB at the timing of netting. 'Honeycrisp' required more open bloom to set a full commercial crop, without the need for thinning, than 'SweeTango' or 'Fuji'. Netted 'Fuji' canopies produced higher fruit set and yield than netted 'SweeTango' and could achieve a relatively high fruit set even when netted at pink. In all cases, fruit set, yield, and seed number of netted trees were significantly reduced compared to the non-netted controls. Individual fruit weight was significantly increased under netting due to reduced crop load. Bee exclusion with nets may constitute an alternative, viable strategy to manage fruit set but will require fine-tuning depending on the cultivar and/or climate.