Reducing ground and airborne drift losses in young apple orchards with PWM-controlled spray systems

Abstract

Pulse Width Modulated (PWM) solenoid valves can be used to control nozzle flow rates for precision spray applications to reduce pesticide use, thereby reducing environmental risk and production cost. Field tests in a two-year-old young apple orchard were conducted to investigate spray losses to the ground and in the air for an air-blast sprayer equipped with three spray systems: 1) manually controlled constant-rate system enabled with the PWM spray system (Manual-PWM), 2) laser-guided variable-rate system enabled with the PWM spray system (Laser-PWM); and 3) conventional constant-rate system with disabled PWM valves (Disabled-PWM). Artificial targets (plastic plates and water sensitive papers) were placed under twelve trees randomly selected from four rows of the orchard to collect spray losses to the ground. Airborne spray losses were determined by using nylon screens, mounted at five heights on each of seven poles distributed at different distances from the first sprayed row. Laser-PWM and Manual-PWM produced significantly lower airborne and ground spray drift losses inside and outside the orchard than Disabled-PWM, and these losses decreased significantly as the distance away from the first sprayed row increased. Laser-PWM reduced the total airborne drift by 90.3% and total ground loss by 85.0% compared to Disabled-PWM whereas Manual-PWM decreased the same airborne and ground drift by 84.1% and 7.9%, respectively. Disabled-PWM produced detectable airborne losses that reached 88.4 m away from where the sprayer was operated. Thus, the air-blast orchard sprayer equipped with PWM solenoid valves controlled by either the automatic laser-guided system or manual system would have great potentials to improve pesticide application efficiency with significant reductions in both pesticide consumption in young apple orchards, and off-target drift loss to the environment.