Assessing the aerial application for mountain orchard sanitation management practices: effects of tree shape on spray distribution in citrus

BACKGROUND: Chemical spray-based pest and disease control in mountainous citrus orchards presents operational challenges. Although aerial application technologies have been widely studied, the spray performance of manned helicopters under complex terrain, particularly during the post-harvest orchard sanitation period, remains insufficiently applied. Furthermore, citrus tree shape may considerably influence droplet deposition. Therefore, a field experimental study was conducted to evaluate the feasibility and operational stability of manned helicopter spraying in mountainous citrus orchards. RESULTS: Droplet deposition exhibited a clear spatial pattern of top mountain (TM) > bottom mountain (BM) > middle mountain (MM), with significantly higher deposition at TM than at MM (P < 0.05). Flight altitude significantly affected droplet deposition, and T2 (flight altitude of 10 m) achieved the best deposition uniformity, outperforming T1 (7 m) and T3 (13 m). Within the TM area, open-center (OC) trees consistently showed higher droplet coverage than round-head (RH) trees, with maximum values up to 1.49 times greater, whereas RH trees exhibited higher coverage in the BM area. Frequency distribution analysis further indicated a more concentrated droplet deposition distribution within OC canopies. CONCLUSION: Maintaining the flight altitude of approximately 10 m above the canopy can improve the spraying effectiveness of manned helicopters in mountainous citrus orchards during post-harvest sanitation. Moreover, optimizing trees according to hillside position may further enhance droplet deposition, with OC shapes better suited for TM and RH shapes more favorable for BM. This study can provide practical guidance for precise and efficient helicopter-based sanitation spraying in mountainous citrus orchards. © 2026 Society of Chemical Industry.