Efficacy evaluation of low-volume concentrate application of pesticides by unmanned aerial vehicle (UAV) using an indoor spraying device

To optimize operating conditions and the selection of pesticides suitable for spraying from UAVs, we evaluated the coverage of sprayed droplets in the range of 0.001–100% coverage by constructing an indoor spraying device. With the device, the coverage rate decreased with the horizontal distance from the nozzle, and the complementary log–log transformed value of the coverage was approximated by a quadratic function of the distance. The natural logarithm of the deposited pesticide amount could be linearly expressed by the complementary log–log transformed value of the coverage. Different probit regression equations were obtained between the coverage rate of sprayed droplets and egg mortality of Panonychus citri due to four acaricides: spiromesifen, etoxazole, milbemectin, and acynonapyr. From the probit regressions, conventional spraying achieved 90% egg mortality with 150 mg/L spiromesifen (19–23% coverage rate), 50 mg/L etoxazole (14%), 10 mg/L milbemectin (98%), and 67 mg/L acynonapyr (92%). Ultra-low-volume concentrate spraying for UAVs achieved the same with 15,000 mg/L spiromesifen (0.017%), 5000 mg/L etoxazole (1.116%), 1000 mg/L milbemectin (1.339%), and 6667 mg/L acynonapyr (8.868%).