Effect of UAV operational parameters on target and non-target spray deposition and efficacy of spider mites and thrips control in cotton

Conventional ground spraying systems in cotton crops often result in inadequate agrochemical application due to taller crop height, non-uniform spray distribution, lower spray efficacy, boll damage, crop injury caused by movement between crop rows, and soil compaction. In this context, unmanned aerial vehicles (UAVs) have emerged as a promising alternative owing to their high operational efficiency, improved droplet deposition, reduced labor requirements, lower operator health risks, and adaptability to varying crop stages and field conditions. Keeping the above problems, present study provides the first systematic assessment of combined effects of flying height and flying speed on limited research exists on their optimization for controlling spider mites and thrips in cotton. However, limited research has systematically investigated the combined effects of UAV flying height and flying speed on spray deposition characteristics and pest control efficacy against spider mites and thrips in cotton crops. Therefore, the present study evaluated the effects of hexacopter UAV at three flying heights (2, 2.5, and 3 m) and three flying speeds (3, 3.5, and 4 m/s) using a factorial randomized block design. The results demonstrated that a flying height of 2 m and flying speed of 3 m/s produced the most effective spray performance throughout the cotton canopy. Under these optimized conditions, droplet density (43.00–48.50 droplets/cm²), droplet size (250.92–256.48 µm), spray coverage (7.70–8.85%), and spray deposition (0.668–0.759 µL/cm²) were maximized across the upper, middle, and lower canopy zones. Spray drift was substantially reduced, with drift percentages of 15.33%, 8.93%, and 4.82% recorded at 2, 4, and 6 m from the central spray line, respectively, and no detectable drift beyond 6 m. The optimized operational parameters also achieved high control efficacy against spider mites (88.78–92.66%) and thrips (90.21–95.65%) at 10 days after application. In addition, the maximum field efficiency (56.02%), application rate (46.66 L/ha), and cotton yield (2546.56 kg/ha) were obtained under the optimized treatment combination. The findings of this study provide scientific guidance for optimizing hexacopter UAV spraying parameters to improve pesticide application efficiency, minimize spray drift and ground loss, and support sustainable precision crop protection in cotton production systems.