Studies in precision crop load management of apple

The number of fruits that remain on an apple tree directly affects yield, fruit size and the quality of fruit that are harvested, which largely determines crop value. If the number of apples can be precisely managed the final crop value can be maximized. We are conducting a USA national SCRI project to develop precision crop load management strategies and machines to manage the number of fruits per tree to exactly the economic optimum. We have done physiological experiments to define the biological potential of yield and fruit size of ‘Gala’ and ‘Honeycrisp’ apple cultivars in 4 sites (West, Mid-West, North-East and South-East USA) to estimate the economic optimum number of fruits per tree. To determine the optimum fruit number per tree we employed: 1) precision pruning to remove flower buds at pink bud stage to various pre-determined flower bud loads followed by hand thinning to single fruitlets at 10mm fruit size; and 2) precision hand thinning to remove fruitlets on uniformly pruned trees to establish different crop loads at 10mm fruit size. Our results showed that the dry, high light climate of WA generally can support a higher crop load than the eastern USA growing regions. Our multi-location experiments demonstrated that leaving too many flower buds during pruning results in lower crop value than the optimum flower bud number. Optimum flower bud number in our studies of ‘Gala’ and ‘Honeycrisp’ was between 1.5 and 2.0 flower buds per final target fruit number. To simplify counting of flowers or fruitlets, we are developing computer vision systems to streamline the counting of buds, flowers and fruitlets. The information from each tree is geo-referenced and cloud-stored therefore can be communicated to human workers to guide their work in reducing crop load to the optimum level.