Field evaluation of an unmanned aerial vehicle (UAV) sprayer: effect of spray volume on deposition and the control of pests and disease in wheat

BACKGROUND: Unmanned aerial vehicles (UAVs) are a recently developed aerial spraying technology. However, the effect of spray volume variation on deposition and pesticide control efficacy is unknown. The effect of three UAV spray volumes (9.0, 16.8 and 28.1\ua0L ha ) using three different nozzle sizes on droplet deposition and wheat aphid and powdery mildew control efficacy was assessed. An electric air-pressure knapsack (EAP) sprayer was used as a comparison. RESULTS: Different spray volumes significantly influenced the deposition and control efficacy of the UAV and EAP. For the UAV, a low spray volume of 9.0\ua0L ha with a fine nozzle (nozzle LU120-01) resulted in lower deposition and control efficacy. Optimal control efficacy was achieved with coarser nozzles (nozzles LU120-02, -03) at > 16.8\ua0L ha volume with systemic insecticide, and at 28.1\ua0L ha with contact insecticide and fungicide. For EAP, a high spray volume led to run-off, and a spray volume of 225 L ha achieved better deposition and control efficacy. CONCLUSION: The UAV had comparable deposition and efficacy control to the EAP at a higher spray volume (> 16.8\ua0L ha ) with coarse nozzles, but exhibited inferior deposition and efficacy control at a lower spray volume