<i>Evaluation of PWM technologies for pesticide spray applications in a two-year old apple orchard</i>

Abstract

Utilization of pulse width modulation (PWM) controlled nozzles may mitigate the off-target losses generated during pesticide treatments. Assays in two-year old apple trees were conducted to evaluate spray quality in a single pass of three systems retrofitted in an airblast sprayer: 1) constant-rate with PWM nozzles controlled with a manual emission system; 2) variable-rate with PWM nozzles controlled automatically with a laser-guided intelligent spray system and 3) constant-rate without PWM controls. Stainless steel screens and water sensitive papers were selected as collectors for measuring the spray deposition and coverage on twelve trees randomly selected from four downstream rows. Plastic plates placed on the ground and nylon screens mounted at five heights on seven poles were used to assess ground and airborne drifts. Data showed that a single pass for each system provided adequate leaf deposits and coverage for the first two rows, but the disabled and manual PWM modes probably incurred over-spray problems. The automatic PWM controlled variable-rate mode guaranteed the number of droplets per unit area required to control insects and diseases, and used the lower application rate with lower ground and airborne drifts than the two constant-rate modes. Results suggested that a single spray pass from each of the three systems could provide adequate spray deposits and coverage in the first two rows, reducing economic costs, but the automatic PWM control could reduce more off-target losses, contributing more efficient spray applications than both conventional and manual PWM controlled constant-rate systems.