Influence of UAV Flight Pattern on Droplet Deposition in Citrus Canopies

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.