Management of external boll rot in cotton using optimized UAV-based fungicide application

Efficient fungicide delivery within dense cotton canopies limits control of canopy-associated diseases such as external boll rot. This study evaluated the effects of UAV spray parameter optimisation on canopy deposition and disease control under semi-arid conditions. A three-factor, three-level orthogonal design assessed spray volume (18, 20 and 22 L ha−1), flight height (2, 3, 4 m) and flight velocity (3.5, 4.0, 4.5 m s−1) based on density, uniformity and penetrability. Spray volume had the greatest influence on deposition (p < 0.01), followed by flight velocity, while flight height showed a smaller effect. The optimised combination (20 L ha−1, 2 m, 4.0–4.5 m s−1) enhanced deposition and penetration into inner canopy layers. Field validation over two seasons showed that UAV spraying reduced boll rot severity by 16–19% and increased seed cotton yield by 5% compared to conventional spraying. Results demonstrate that improved deposition enhances disease control and supports UAV-based fungicide application in cotton.