Analysis of factors affecting control effects of pesticide applications against rice sheath blight and Chilo suppressalis in low-volume spray by unmanned aerial vehicle

In this study, the effects of four factors, including flight parameters (flight speed and flight height), spraying-water volume and the type of sprayer-head on control efficacy of fungicide 240 g/L thifluzamide SC against rice sheath blight and insecticide 5% abamectin EC against Chilo suppressalis in low-volume spray by unmanned aerial vehicle Jifei 20 were investigated, respectively. 4 different flight speeds, i.e. 3, 4, 5, 6 m/s were tested. The results showed that the lower of flight speed, the higher of the control efficacies for both rice sheath blight and C. suppressalis. The evaluation of 4 different flight heights, i.e. 1.5, 2.0, 2.5, 3.0 m, were also conducted, which demonstrated that with the flight heights of 2.0 or 2.5 m resulted in significantly higher efficacy against both rice sheath blight and C. suppressalis compared to those with 1.5 or 3.0 m. 3 different spraying-water volumes, i.e. 7.5, 15.0, 22.5 L/hm², were studied which revealed that the increase of the spraying-water volume resulted in higher control efficacy. And the difference among the three treatments was significant for both rice sheath blight and C. suppressalis. In the experiments using two different types of sprayer-head, i.e, centrifugal and pressurized, the difference of control efficacy between them was not significant for both rice sheath blight and C. suppressalis. Hence, the optimal parameters are as follows: flight speed 3-4 m/s, flight height 2.0-2.5 m, and spraying-water 15.0-22.5 L/hm², which will be an important guide for the control of rice pests by unmanned aerial vehicle.