Study of the Effects of Different Spray Adjuvants on Unmanned Aerial Vehicle Crop Protection in Rice Fields

Abstract Unmanned aerial vehicle (UAV) spraying is being increasingly used for rice pest control, but challenges remain in terms of optimizing the uniformity and efficacy of droplet deposition. In this study, the effects of six commercial spray adjuvants on the UAV-based control of rice stem borers in paddy fields were systematically evaluated. With a T30 UAV equipped with water-sensitive paper monitoring, we assessed the droplet spreading dynamics, deposition density, coefficient of variation (CV), and field control efficacy at various heights (1.5–3 m) and speeds (3–6 m/s). The results revealed that Activator 90 significantly reduced the CV by 30% (p<0.01) and resulted in the highest deposition density (30.0 drops/cm2) within 2 minutes. Compared with the control treatment, the Activator 90 increased the control efficacy by 70% to 87%, with optimal parameters at a height of 2.5 m and a spraying rate of 22.5 L/ha. This research reveals that selective adjuvants can markedly improve UAV spray performance, providing a practical framework for precision pest management in rice ecosystems. Competing Interest Statement The authors have declared no competing interest.