Influence of the spray volumes and adjuvants on operational efficacy of plant protection unmanned aerial vehicle at the seedling stage of cotton

In order to explore the influence of the spray volumes and adjuvants on droplet deposition and aphid control efficacy of insecticide, spray tests were carried out by an MG-1P electric-powered multi-rotor plant protection unmanned aerial vehicle (UAV) in a cotton field (seedling stage). Acetamiprid 5% EC was sprayed by UAV under three different spray volumes (15.0, 22.5, and 30.0 L/hm²), and two adjuvants (YS09 and Beidatong). Allura red was used as a tracer in the determination of droplet deposition and pesticide utilization. The droplet density and coverage rate were analyzed by the image processing software Deposit-Scan. The results showed that the droplet density and droplet coverage on the leaves significantly increased with the increase in spray volumes. The droplet density on the adaxial surface and abaxial surface of cotton leaves were higher at the volume of 30.0 L/hm², with the droplet density of 43.42 droplets/cm² and 58.04 droplets/cm², the droplet coverage of 6.44% and 6.34%, respectively. The pesticide utilization rates of different spray volume tests by UAV were 3.53%, 3.70%, and 4.00%, which were lower than that of the knapsack electrostatic sprayer. Moreover, the control efficiencies of these UAV tests on the 1st- and 3rd- day were also lower than that of the knapsack electrostatic sprayer test. The addition of two adjuvants, YS09 and Beidatong, had no significant effect on droplet density, droplet coverage, and pesticide utilization rate on cotton leaves, but improved the control effect on cotton aphids. On the 1st day after spraying, the control efficacies of YS09 and Beidatong treatments were 86.24% and 84.40%, respectively, which increased by 9.34% and 7.48% compared with the control group. On the 3rd day, the control efficacies reached 95.34% and 94.73%, respectively, which were comparable to that of the knapsack electrostatic sprayer (94.36%) but still higher than that of the control group (88.06%). The results indicated that the increase in spray volume could enhance the number of droplets deposited on the leaves and the addition of adjuvant increased the control efficacy of acetamiprid against cotton aphids.