2019 ASHS Annual Conference

Organic apple production is increasing worldwide. Limited availability of chemical products to manage insects and crop load, via thinning, present major barriers to organic apple production. Application of exclusion netting in apple orchard systems demonstrably mitigates abiotic stress and pest pressure. The objective of this experiment was to use exclusion netting to additionally manage the crop load of ‘Gala’ apple trees by whole-tree enclosure at different stages of bloom. Ten trees per replication were fully enclosed by netting when a pre-defined percentage of open bloom was reached. Treatments included 1) Non-netted, non-thinned control, 2) Non-netted, hand-thinned control, 3) netting at Pink (no flowers open), 3) netting at 20% King Bloom; 4) netting at 40% King Bloom, or 5) netting at 80% King Bloom. Fruit set, yield, PAR, fruit size, seed content, fruit quality attributes and return bloom were assessed. Nets had only a slight effect on fruit set. In 2017, trees completely enclosed in netting at pink had 45% fruit set compared to 65% fruit set of non-netted trees. Further, non-netted control fruit had average seed counts of 4 compared to 1.5 for net treatments. Low seed counts in control fruit was due to frost events. Nets did not significantly affect the number of fruit or yield but there was a tendency for smaller fruit inside of nets. In 2018, we observed a similar response on fruit set. Differences in fruit weight were slightly more pronounced: hand-thinned and non-thinned controls were 145 g and 135 g, respectively, compared to 120 to 130 g inside nets. The number of mature seeds per fruit, however, was markedly higher in 2018 given frost-free conditions. Non-netted trees had ~7.4 seeds per fruit versus ~ 5 for net treatments. The number of non-fertilized seeds was 4.1 for non-netted controls and 6.5 to 7 for net treatments. Despite a high seed content of netted trees, especially those netted at pink, the small orifices of the netting effectively excluded pollinators (including native pollinators). Our data support earlier reports of self-fertility in Gala. We do not dismiss the role of wind pollination to aid ‘Gala’ self-fertility and the possible contribution of pollen from pollinizer trees in the orchard. The use of exclusion netting to manage crop load does not appear viable in Gala due to self-fertility, but additional research to characterize the effects of netting on thinning of different cultivars and fruit size is warranted.