Synergistic Mechanisms of UAV Spray Parameters and Reduced Nano-Pesticide Application in High-Density Maize Canopies

To address the plant protection challenges of high canopy closure and poor droplet penetration in high-density maize, this study systematically elucidated the synergistic regulatory mechanisms of UAV operational parameters and reduced nano-pesticide application. Integrating laboratory microscopic characterization with a two-phase field experiment, this study evaluated spray volume, droplet size, and pesticide dosage as core variables. Phase I quantified the effects of physical spray parameters on droplet deposition and penetration characteristics, while Phase II comprehensively revealed the field control efficacy under multi-factor synergy. Results showed that 22.5 L/ha achieved the optimal balance; it increased deposition density by 109.0% compared to 15.0 L/ha (p < 0.05) while maintaining comparable efficacy to 30.0 L/ha without sacrificing operational efficiency. The 200 μm droplets demonstrated superior penetration, increasing lower-layer coverage by 33.9% compared to 300 μm (p < 0.05), and overcoming the evaporation limitations of 100 μm (which showed no significant efficacy improvement despite higher density, p > 0.05). Microscopic measurements confirmed that nano-pesticides exhibited excellent wetting dynamics, reducing the final contact angle on hydrophobic maize leaves to as low as 28.24° (achieving a maximum dynamic reduction rate of 54.48%), significantly enhancing interfacial adhesion. This mechanism compensated for low-volume spraying limitations, allowing a 30% dosage reduction to maintain a robust field efficacy of 90.6%, whereas a 50% reduction significantly compromised efficacy (<72.5%). Ultimately, this study established “22.5 L/ha + 200 μm + 30% reduction” as the optimal operational parameter combination, providing a solid theoretical foundation and crucial technological support for precision plant protection and “pesticide reduction with efficiency enhancement” in high-density maize cultivation.