Coverage and drift potential associated with nozzle and speed selection for herbicide applications using an unmanned aerial sprayer

In recent years, unmanned aerial vehicle (UAV) technology has expanded to include UAV sprayers capable of applying pesticides. Very little research has been conducted to optimize application parameters and measure the potential of off-target movement from UAV-based pesticide applications. Field experiments were conducted in Raleigh, NC during spring 2018 to characterize the effect of different application speeds and nozzle types on target area coverage and uniformity of UAV applications. The highest coverage was achieved with an application speed of 1 m s(-1) and ranged from 30% to 60%, whereas applications at 7 m s(-1) yielded 13% to 22% coverage. Coverage consistently decreased as application speed increased across all nozzles, with extended-range flat-spray nozzles declining at a faster rate than air-induction nozzles, likely due to higher drift. Experiments measuring the drift potential of UAV-applied pesticides using extended-range flat spray, air-induction flat-spray, turbo air-induction flat-spray, and hollow-cone nozzles under 0, 2, 4, 7, and 9 m s(-1) perpendicular wind conditions in the immediate 1.75 m above the target were conducted in the absence of natural wind. Off-target movement was observed under all perpendicular wind conditions with all nozzles tested but was nondetectable beyond 5 m away from the target. Coverage from all nozzles exhibited a concave-shaped curve in response to the increasing perpendicular wind speed due to turbulence. The maximum target coverage in drift studies was observed when the perpendicular wind was 0 and 8.94 m s(-1), but higher turbulence at the two highest perpendicular wind speeds (6.71 and 8.94 m s(-1)) increased coverage variability, whereas the lowest variability was observed at 2.24 m s(-1) wind speed. Results suggested that air-induction flat-spray and turbo air-induction flat-spray nozzles and an application speed of 3 m s(-1) provided an adequate coverage of target areas while minimizing off-target movement risk.