## 2 Materials and Methods
### Spray Equipment  
A battery motive 3 WTXC8-5 six-rotor UAV (Henan Tianxiucai Aviation protection machinery Co., Ltd., Kaifeng, China) (Figure 1A) was used in this study. The UAV was powered by two 12,000 mAh Li-Po batteries (Shenzhen Grepow battery Co., Ltd., Shenzhen, China). The flying time was 15-20 min with full tank. The flight speed was 12.6-14.4 km/h with two rotary cup atomizer arranged on both sides. The interval of nozzles was 0.85 m and the installation angle was vertically downward. The rotate speed of the disk was 10,000 rotations per minute. The chemicals were transferred from the tank to the nozzles by a HXB600 micro liquid pump (Shanghai Hallya Electric Co., Ltd., Shanghai, China) and the flow rate was 1.24 L/min. The accuracy of the flight height and flight velocity were controlled by the well-trained operator. The flight height was 1.0 m and the effective spraying width was 4.0 m. The spray volume of one sortie was close to 10 L/ha, which was equal to two times the tank capacity.  
One of the comparison systems was the 3 WX-280H self-propelled boom (SPB) sprayer produced by Sino-Agri Fengmao Plant Protection Machinery Company (Beijing, China) with the tank capacity of 280 L (Figure 1B). There are 12 ISO 04 nozzles (Spraying system Co.) installed vertically on the spray boom with the same interval of 0.5 m on the 6-m boom. The spraying height of the boom was 0.5 m from the top of the canopy. The spray pressure was 4 bar and the flow rate was 18.2 L/min. The operation speed was 6.0-6.5 km/h. Under these application conditions, the spray volume was close to 300 L/ha.  
The two other conventional sprayers were WFB-18 knapsack mist-blower (KMB) sprayer (Sino-agri Fengmao, China) (Figure 1C) and 3 WBS-16A2 electric air-pressure knapsack (EAP) sprayer (Chuangxing sprayer factory, Xinxiang, China) (Figure 1D). EAP sprayer was equipped with twin hollow cone nozzles and a pressure pump provided a maximum pressure of 4 bar and a flow rate of 1.6 L/min. The tank capacity was 16 L and the length of the lance of the EAP sprayer was 81 cm. The spray swath width was close to 2.5 m. The traveling speed in the test was approximately 1.1-1.3 km/h and the spray volume under these application conditions was close to 300 L/ha. The KMB sprayer was developed to improve the spraying efficiency of air-pressure knapsack sprayer, which was equipped with a tank, a spray pipe, a nozzle and a gasoline engine. The droplets were sprayed from the nozzle, which were further atomized by the high speed air flow. The high speed air flow was produced by high speed whirling impeller driven by the gasoline engine. The flow rate in this test was 2.0 L/min with the tank capacity of 18 L. The spraying swath width was close to 6.0 m. The traveling speed was approximately 2.7-3.0 km/h and the spray volume was close to 75 L/ha. The working height of the nozzle of two conventional sprayers was 0.5 m from the top of the canopy. The spraying patterns of two knapsack were both swinging spraying.  
All working parameters and spray volumes for each sprayer were established taking into account local farmers practices. Before tests, all spray equipment performed a preliminary test to calibrate the equipment to ascertain the flow rate of the nozzles. After the flow rate was ascertained, the traveling speed was also calculated to obtain the stated application rate. To achieve the velocity, the operator needed to repeat several times before undertaking each trial until the desired traveling speed was reached. Each spraying treatment was done by a well-trained applicator.  
Figure 1: Four test sprayers: (**A**) 3 WTXC8-5 six-rotor unmanned aerial vehicle (UAV) sprayer; (**B**) 3 WX-280H self-propelled boom (SPB) sprayer; (**C**) WFB-18 knapsack mist-blower (KMB) sprayer; and (**D**) 3 WBS-16A2 electric air-pressure knapsack (EAP) sprayer.