Analysis of droplet deposition and maize (Zea mays L.) growth control: Application of ethephon by small unmanned aerial vehicle and electric knapsack sprayer

Maize (Zea mays L.) is a major global crop, but lodging leads to yield loss. Ethephon can regulate maize growth, reduce plant height, and improve lodging resistance. The application of small crop protection unmanned aerial vehicles (UAV) to replace electric knapsack sprayers (EKS) for the mechanization of agriculture in China has been widely developed. However, there are no reports on the application of ethephon to control maize growth by UAV. In the present study, the effects of spraying by UAV (15 L ha−1 and 30 L ha−1) and EKS (450 L ha−1) on the droplet deposition distribution and dynamic degradation process of ethephon (60 g a.i. ha−1) were studied. The control of maize growth by different ethephon dosages was also investigated, i.e., 48, 60, and 90 g a.i. ha−1 for UAV and 60 g a.i. ha−1 for EKS. The droplet deposition rates of 15 L ha−1 and 30 L ha−1 by UAV were 11.2% and 15.2%, significantly higher than those of EKS. Furthermore, the degradation half-life under UAV application was longer than that under EKS. The 20% dosage reduction of ethephon applied by UAV (48 g a.i. ha−1) had the same maize growth control effect as EKS (60 g a.i. ha−1), and the UAV treatment was better than EKS when the dosage was the same (60 g a.i. ha−1). Considering the input cost and yield, we recommend that 48 a.i. g ha−1 ethephon is applied by UAV when the lodging risk is low and 90 a.i. g ha−1 when the lodging risk is high, at a spray volume of 15 L ha−1. The application cost of ethephon can be reduced by 47.91–71.81% compared to EKS under these conditions.