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Abstract. Agricultural unmanned aerial vehicle (UAV) technology has been developed rapidly in China during recent 10 years. Due to the high application efficiency, all-terrain spraying capability as well as the low volume spraying application techniques, the agricultural UAV was widely used in pest control of field crops, which has achieved good control effects and reduced the pressure of rural labor shortage. In this paper, the applicability of UAV in orchard plant protection was tested in an apple orchard, spraying by using the four-rotor multi-rotor electric UAV and the conventional air-assisted orchard sprayer. The spray characteristics of both sprayers such as canopy deposition, drift in the air, ground loss as well as the pesticide pollution on machine appearance were measured and compared.

Field results showed that the effective spray swath width of the UAV was 2.23m, and the maximum droplet density of the central route was 132/cm². The actual deposition in canopy of UAV was lower than that of orchard sprayer, but the normalized deposition was equivalent to orchard sprayer, and the coefficient of variation of deposition in all parts of tree was obviously higher than orchard sprayer. Due to the effect of the air flow produced by high-speed revolving rotors, the amount of spray drift in the air was much higher than orchard sprayer, whereas the ground loss was 1/5 of the orchard sprayer. Meanwhile, the rotor air flow of UAV causes a large amount of droplets to adhere to the fuselage, caused the amount of external contamination on the UAV was five times than that of the orchard sprayers.

Trials pointed out that the use of multi-rotor electric UAV for plant protection in orchard has a considerable influence on the spray drift and external contamination of the equipment. On the basis of these first data it will be possible to provide indications: a) plant protection UAVs should be sprayed at a reasonable height to reduce the drift in the air; b) to UAV manufacturers for the development of adequate spraying system as well as for an appropriate design of UAV for plant protection.