In-field sensing for crop protection: Efficacy of air-blast sprayer generated crosswind in rainwater removal from cherry canopies

Rainwater-induced fruit cracking leads to serious economic loss to fresh market sweet cherry growers. To prevent fruit cracking, the key is timely and effective removal of rainwater from canopies during and after rain events. Current rainwater removal methods include use of orchard air-blast crosswind and manned helicopter downwash based on empirical judgement of growers. The goal of this study was to develop an in-field sensing system to monitor canopy wetness and micro-climate, which will help growers to decide upon when and how much rainwater needs to be removed from canopies. The developed sensing system was tested to evaluate the efficacy of an air-blast orchard sprayer in rainwater removal from cherry trees with Y-trellised (Skeena) and vertical (Selah) architectures. Results show that the sensing system could capture the wetness threshold rainfall level that may cause fruit cracking (2.5 mm). Crosswind generated by the orchard sprayer was unevenly distributed on tree canopies, especially in vertical architecture, where crosswind velocity in bottom-section of canopies (1.1 m above ground) was significantly higher than that in middle- (1.9 m) and top-sections (2.7 m). Overall, orchard sprayer crosswind had the highest rainwater removal than natural drying (control) in both architectures. Rainwater removal was significantly affected by rainfall levels studied, with significantly higher in lower rain level (2.5 mm) than those of medium (5.0 mm) and high level (10 mm) from vertical tree canopies. Also, in vertical architecture, the interaction effect of travel speed and location was significant on rainwater removal, and the rainwater removal due to crosswind at any travel seed was significantly higher than that of control at middle section of vertical tree canopies.