Best Use Practices to Optimize Pesticide Applications from Pulse-Width Modulation Sprayers.

Pulse-width modulation (PWM) spray application systems allow for variable rate control of flow by pulsing an electronically‑actuated solenoid valve placed directly upstream of the nozzle. Flow is changed by controlling the relative proportion of time each solenoid valve is open versus closed (duty cycle). PWM sprayers allow for the precise control of individual nozzles, without manipulating application pressure, increasing the accuracy and uniformity of applied spray droplets. The objective of our research was to evaluate PWM sprayer application parameters, specifically duty cycle, nozzle type, and application pressure effect on nozzle tip pressure, droplet size, and droplet velocity to create best use practices for PWM sprayers.

Two experiments were conducted using a SharpShooter® PWM system in low‑speed wind tunnels at the Pesticide Application Technology Laboratory in North Platte, NE and the Aerial Application Technology Laboratory located at the USDA‑ARS Southern Plains Agricultural Research Center in College Station, TX. One experiment measured droplet size using a Sympatec HELOS-VARIO/KR laser diffraction system and nozzle tip pressure using a pressure transducer installed inline between the PWM solenoid valve and nozzle. Analog electrical signals from the transducer were sampled at a 100 Hz rate for five seconds with an Arduino Mega 2560 board. The second experiment measured droplet velocity using the LaVision SprayMaster Shadowography high‑speed image analysis function.

Generally, results indicated droplet size increased as duty cycle decreased, and average droplet velocity decreased as duty cycle decreased. Nozzle tip pressure measurements showed solenoid valves contain a restriction which causes a pressure loss across the valve. Air inclusion nozzles had greater variability across measurements taken when pulsed compared to non‑air inclusion nozzles. The 20% duty cycle had greater variability across measurements taken compared to other duty cycles. This research is critical for the optimization of pesticide applications through better utilization of PWM sprayers.