Spray drift evaluation from a four-axis unmanned aerial spraying system: effects of spray parameters under different...

Unmanned aerial spraying systems (UASSs) are increasingly used in crop protection. There are, however, considerable concerns regarding pesticide drift during their field application, which poses potential environmental risks. Reducing drift while maintaining efficiency is therefore critical. In this study, an octocopter UASS with centrifugal nozzles was tested under varying spray parameters using a modified ISO 22866 method. The effects of droplet size, flight speed and flight height on target deposition and downwind drift were evaluated under two crosswind conditions, and UASS performance was compared with that of a conventional boom sprayer.

The downwind cumulative drift percentage of the UASS is 62.8-811.7%, which is 1.5-17.9 times that of boom sprayers, depending on the operational parameters of the UASS. Droplet size, flight speed and flight height had significant effects on UASS drift, while flight height was the most critical in determining droplet drift and deposition. Droplet size exerted a stronger influence on airborne drift than flight speed, while neither droplet size nor flight speed had a significant impact on target-area deposition. Lowering the flight height to below 3 m should be considered first to reduce drift risk during operations.

This study provides quantitative evidence on the influence of spray parameters on UASS drift behavior and highlights strategies to mitigate drift risks. The findings offer valuable guidance for parameter optimization in UASS field spraying, thereby supporting environmentally safer pesticide applications and promoting cleaner agricultural production. © 2026 Society of Chemical Industry.