Deposição de gotas e eficácia do glufosinato de amônio aplicado com Aeronave Remotamente Pilotada (ARP) no controle de Conyza spp.: influência da vazão e do tamanho de gota

Abstract

Spraying with Remotely Piloted Aircraft (RPA) operates with drastically reduced spray volumes (7 to 10 L ha⁻¹) compared to conventional ground methods, imposing the challenge of ensuring sufficient deposition for the efficacy of contact herbicides, such as glufosinate ammonium, used in the management of hairy fleabane (Conyza spp.) in soybean pre-sowing. This study aimed to evaluate combinations of spray volume and droplet size that maximize target deposition, provide effective weed control, and minimize drift risks. The experiment was conducted in a completely randomized design with six replications, using a DJI Agras T40 drone in a commercial area in the municipality of Lindoeste, PR, Brazil. Eight treatments were tested, resulting from the combination of two spray volumes (7 and 10 L ha⁻¹) and four droplet sizes (100, 200, 300, and 400 μm). Deposition was evaluated using water-sensitive papers, analyzing volume median diameter (VMD), covered area (%), droplet density (droplets cm⁻²), and potential drift risk. Hairy fleabane control efficacy was visually assessed at 7 and 14 days after application (DAA), according to the Brazilian Society of Weed Science (SBCPD) methodology. Data were subjected to analysis of variance and regression analysis. Treatments T2 (7 L ha⁻¹ + 200 μm) and T8 (10 L ha⁻¹ + 400 μm) showed the best results, with covered areas of 2.69% and 2.84%, and droplet densities of 79.18 and 57.42 droplets cm⁻², respectively, not differing statistically from each other. Treatment T4 (7 L ha⁻¹ + 400 μm) showed the poorest performance (0.34% coverage). Regression analysis revealed a quadratic relationship between droplet size and covered area, with maximum estimated points at 215 μm (R² = 0.99) for 7 L ha⁻¹ and at 380 μm (R² = 0.58) for 10 L ha⁻¹. Regarding biological efficacy, treatment T5 (10 L ha⁻¹ + 100 μm) provided the highest absolute control at 14 DAA (≈95%), while T2 and T8 showed satisfactory control (≈82% and 64%, respectively), combining good deposition with adequate levels of hairy fleabane suppression. The VMD range between 200 and 300 μm provided the best balance between coverage (>2.5%), density (>50 droplets cm⁻²), and drift risk (<15%). It is concluded that configurations T2 (7 L ha⁻¹ + 200 μm) and T8 (10 L ha⁻¹ + 400 μm) are the most suitable for glufosinate ammonium application via RPA, recommending droplets in the 200–300 μm range to reconcile agronomic efficacy and drift mitigation. "This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001."