Optimizing pesticide delivery in cotton: impact of unmanned aerial spraying system configurations on canopy deposition and implications for pest control efficacy.

BACKGROUND: Effective management of insect pests and diseases in cotton, such as aphids, whiteflies and bollworms, is critically dependent on achieving adequate pesticide coverage throughout the plant canopy. Conventional ground spraying methods are often inefficient and can damage crops, whereas the adoption of unmanned aerial spraying systems (UASS) presents a promising alternative. However, the efficacy of UASS applications is highly dependent on system configuration, and a lack of data on spray deposition within dense cotton canopies hinders the development of effective application protocols. This study investigates how different UASS designs and operational parameters influence pesticide delivery, providing a basis for optimizing pest control strategies. RESULTS: A field study was conducted in Xinjiang, China, to evaluate the spray performance of 10 distinct UASS in a mature cotton canopy. We found that spray deposits decayed sharply from the upper to the lower canopy layers, posing a critical challenge for controlling pests residing in the mid-to-lower canopy. The choice of UASS configuration significantly influenced spray distribution. Autonomous flight modes provided superior transverse spray uniformity compared to the manual control, ensuring more consistent coverage and reducing the risk of underdosed areas where pests could survive. Multirotor UASS feature a relatively uniform downwash airflow field that improves spray deposition and distribution performance, whereas oil-powered models, compared to electric ones, suffered from unstable airflow, leading to poorer uniformity. Centrifugal nozzles demonstrated superior performance for mid-canopy deposition. A random forest analysis identified control mode, main rotor number and nozzle type/quantity as the most critical parameters influencing deposition patterns. CONCLUSION: The configuration of a UASS is not a trivial detail but a critical factor determining the potential for effective pest control in cotton. To maximize biological efficacy, particularly against canopy-dwelling pests, spray protocols should prioritize autonomous, multirotor UASS equipped with appropriate nozzles to enhance deposition and penetration. These findings provide a scientific framework for developing targeted UASS application guidelines that can improve pesticide-use efficiency, reduce off-target losses, and form an integral component of modern, sustainable pest management programs in cotton. © 2026 Society of Chemical Industry.