In mountainous citrus orchards, the application of conventional ground sprayers for the control of citrus red mite (Panonychus citri) is often constrained by complex terrain and low operational efficiency. The Unmanned Aerial Spraying System (UASS), due to its low-altitude, low-volume, and high-maneuverability characteristics, has emerged as a promising alternative for pest management in such challenging environments. To evaluate the spray performance and field efficacy of different UASS types in controlling P. citri, five representative UASS models (JX25, DP, T1000, E-A2021, and T20), four mainstream pesticide formulations, and four novel tank-mix adjuvants were systematically assessed in a field experiment conducted in a typical hilly citrus orchard. The results showed that T20 delivered the best overall spray deposition, with upper canopy coverage reaching 10.63%, a deposition of 3.01 μg/cm², and the highest pesticide utilization (43.2%). E-A2021, equipped with a centrifugal nozzle, produced the finest droplets and highest droplet density (120.3–151.4 deposits/cm²), but its deposition and coverage were lowest due to drift. Nonetheless, it exhibited superior penetration (dIPR 72.3%, dDPR 73.5%), facilitating internal canopy coverage. T1000, operating at higher flight parameters, had the weakest deposition. Formulation type had a limited impact, with microemulsions (MEs) outperforming emulsifiable concentrates (ECs) and suspension concentrates (SCs). All adjuvants improved spray metrics, especially Yimanchu and Silwet, which enhanced pesticide utilization to 46.8% and 46.4% for E-A2021 and DP, respectively. Adjuvant use increased utilization by 4.6–11.9%, but also raised ground losses by 1.5–4.2%, except for Yimanchu, which reduced ground loss by 2.3%. In terms of control effect, the rapid efficacy (1–7 days after application, DAA) of UASS spraying was slightly lower than that of ground sprayers—electric spray gun (ESG), while its residual efficacy (14–25 DAA) was slightly higher. The addition of adjuvants improved both rapid and residual efficacy, making it comparable to or even better than ESG. E-A2021 with 5% abamectin·etoxazole ME (5A·E) and Yimanchu achieved 97.4% efficacy at 25 DAA. Among UASSs, T20 showed the rapid control, while E-A2021 outperformed JX25 and T1000 due to finer droplets effectively targeting P. citri. In residual control (14–25 DAA), JX25 with 45% bifenazate·etoxazole SC (45B·E) was most effective, followed by T20. 5A·E and 45B·E showed better residual efficacy than abamectin-based formulations, which declined more rapidly. Adjuvants significantly extended control duration, with Yimanchu performing best. This study demonstrates that with optimized spraying parameters, nozzle types, and adjuvants, UASSs can match or surpass ground spraying in P. citri control in hilly citrus orchards, providing valuable guidance for precision pesticide application in complex terrain.

Pests and diseases can lead to a decline in citrus fruit quality and yield. Unmanned Aerial Vehicle (UAV) spraying provides rapid field operation and strong adaptability to complex terrain, and low-altitude, low-volume spraying for orchard pest management. However, existing studies have not yet fully clarified how different UAV flight patterns affect droplet deposition within citrus canopies and the surrounding space. This study evaluated two flight patterns using an XAG P20 UAV: flight pattern 1, parallel to the citrus tree rows, and flight pattern 2, perpendicular to the tree rows. Rhodamine B was used as a tracer, and Mylar cards were placed in the upper, lower outer, and lower inner canopy layers and on sampling rods around the trees. Total canopy deposition, deposition uniformity, canopy penetration, and rod-position deposition were analyzed. Flight pattern significantly affected total canopy deposition (F = 28.486, p = 0.0059). Compared with flight pattern 1, flight pattern 2 increased total canopy deposition by 72.19%. Deposition in the upper and lower inner layers increased by 88.40% and 94.31%, respectively, while canopy penetration increased from 28.23% to 34.15%. For both flight patterns, deposition on sampling rods located directly beneath the UAV flight path was significantly higher than that on rods located away from the flight path, by approximately 6.8 and 6.4 times for Patterns 1 and 2, respectively. Overall, flying perpendicular to the citrus tree rows improved total canopy deposition, inner-canopy deposition, and canopy penetration. This study provides a reference for optimizing UAV spraying patterns in citrus orchards and improving effective droplet deposition within the canopy, thereby contributing to safeguarding citrus yield and fruit quality.