Impact of rice field drone applications on canopy dynamics of rice planthopper populations

The downwash airflow from plant protection UAVs disturbs rice planthoppers. This study investigated airflow-induced pest distribution by testing two UAV models (large-rotor N-3, small-rotor HYB-15L) and four flight heights (0.8–5 m), spraying only pure water to isolate airflow impacts. Field experiments integrated short-term (30 min) and long-term (1, 3, 7 d) monitoring, aerodynamic measurements, and statistical analyses. Results showed significant (P < 0.001) planthopper redistribution: spray swath densities reduced by 41–74%, adjacent 2–10 m zones exhibited density decreases at 2 m (P < 0.05), baseline recovery at 5 m (P > 0.05), and 24–58% increases at 10 m (P < 0.01). Vertically, airflow shifted pests from the lower to upper canopy and ground (P < 0.001), driven by downwash (2.5–3.8 m/s) and rebound airflow (1.2–2.0 m/s). The effect was transient, stabilizing 3 d post-operation. The optimal trade-off was the N-3 UAV at 3 m, achieving 73.9% spray swath reduction and 0.48 ha/h work rate. These findings clarify UAV parameter impacts on planthopper dispersion, guiding optimized integrated pest management in rice.