Optimizing UAV Spraying for Sustainability: Different System Spray Drift Control and Adjuvant Performance

Agricultural spraying, despite modern technological advances, still poses the problem of downwind spray drift, which contributes to environmental contamination and ecological imbalance, which are critical sustainability concerns. This study investigated the effect of lateral wind on different unmanned aerial vehicle (UAV) spraying systems under semi-controlled conditions, additionally evaluating the impact of four tank-mix adjuvants (drift reduction agents (DRAs)) at varying concentrations on spray effectiveness, droplet size, and deposition compared to water as a control. By examining UAV-specific spray dynamics, this research provides insights into sustainable drift reduction strategies that minimize environmental impacts. For the UAV spraying performance trials, three UAVs with different spraying configurations were tested, TTA M6E, XAG XP2020, and DJI T30, to identify the most effective system for minimizing downwind spray drift. For the DRA effectiveness trials, four commercially available adjuvants were evaluated at different concentrations utilizing the T30 UAV, which was chosen because it produces the highest proportion of fine droplets. The DRA products included an ionic/non-ionic surfactant (DRA No. 1), silicone-based wetting agents (DRA Nos. 2 and 3), and a silicone-based spreader-adhesive (DRA No. 4). This study showed that, among the tested UAV spray systems, M6E and XP2020 performed better in low-wind conditions, while T30 was more suitable for stable target area deposition in windy conditions but produced higher quantities of fine droplets prone to drifting further. Lateral wind contributes significantly to spray drift, as shown by the results, with increased wind speed causing an additional drift of up to 2 m downwind for all systems. The study also showed that all the tested DRAs exhibit the potential to mitigate drift and improve crop coverage, contributing to more efficient resource use and reduced environmental impacts. All the DRA products either reduce the drift distance by up to 3 m or decrease the deposition by up to 67% compared to water. However, DRA No. 1 showed the best results out of all the tested products in terms of drift control, while DRA No. 4 showed the best target area coverage and adequate drift control capabilities. More field research is required to validate the effectiveness in real-life application scenarios. In summary, the following management measures can be used to control droplet drift using UAV spraying systems, in order of importance: selecting a UAV and nozzles that are optimal for the specific requirements of the spraying task, planning applications in correlation with lateral wind speed, and the use of DRAs.