Localized sensing data-driven efficacy evaluation of heat stress mitigation techniques in ‘Honeycrisp’ apple cultivar

This study was conducted in a commercial ‘Honeycrisp’ apple orchard in 2021 and 2022 season to understand the effectiveness of cyclic evaporative cooling (conventional), continuous fogging, netting and combination of fogging and netting (fognet) in mitigating heat stress on fruits and associated effects on post-harvest fruit quality. Heat stress on fruits was quantified continually during each season using air (T_air) and fruit surface temperature (FST) data collected by a localized crop physiology sensing system. Results indicated that heat stress on fruits in terms of pre- and post-harvest fruit quality was governed by the time for which fruits were subjected to T_air > 32 °C and resultant total heat accumulation. Additionally, effectiveness of heat stress mitigation was influenced by fruits exposure time to direct solar radiation, in season fruit size and crop load. Except netting, all other treatments were effective in removing accumulated heat and maintaining FST below 45 °C fruit sunburn threshold. Although effective, conventional treatment failed to maintain FST below threshold during extreme heat hours (T_air > 32 °C) suggesting adjustments needed in its cyclic operations. FST and T_air data were then contrasted against fruit size, crop load, and percent sunburn at harvest. Similarly, data was contrasted for postharvest performance evaluation, disorders (bitter pit, soft scald) and maturity, until six months of storage. With higher T_air, FST, and smaller fruits, netting delayed fruit maturity in both seasons. Significant difference was observed in bitter pit and soft scald incidence between netting and other treatments only in 2022 season. Insignificant differences in maturity and disorders between fogging, fognet, and conventional implied that fognet has no specific advantage over fogging and conventional cooling technique.