Abstract:

【Objective】The objective of this study is to explore the distribution of droplet deposition in citrus canopy and operation parameters of plant protection by the unmanned aerial vehicle (UAV) sprayer, carry out the test of control effect against citrus psyllid (Diaphorina citri) and citrus leafminer (Phyllocnistis citrella) by UAV in the orchard, evaluate the control effect, operation efficiency and comprehensive benefits of UAV spraying technology, and to provide a basis for the establishment and application of low-altitude and low-capacity UAV spray technology in citrus producing areas.【Method】The experiment was conducted at the high-yielding period of a Citrus paradisi orchard in Wan’an County, Jiangxi Province. Four rows of about 100 citrus trees of natural round shape canopy were cut into open center shape, and four rows of natural round shape were selected as control. The grid frame was set up in the canopy of the sampling plant. The grid frame was divided into three layers in vertical direction, 3×5 sampling points in each layer, a total of 45 pieces of double 4 cm × 6 cm paper cards as droplet carrier were placed on the top, middle and lower parts of citrus tree with 0.5% Temptation Red water solution as tracer. The distribution of the spray droplets in the canopy under different flight operation speeds (v₁=0.7 m·s^-1, v₂=1.2 m·s^-1, v₃=1.7 m·s^-1) and different operating heights (h₁=1.0 m, h₂=1.5 m, h₃=2.0 m) was analyzed with the six-rotor crop protection unmanned aircraft. After each treatment, the paper card was collected and scanned by 300 dpi resolution scanner to calculate the percentage of spreading area of the Temptation Red water solution on the paper card, which was calculated as the droplet coverage rate on the citrus leaves. The deposition distribution of sprayed droplets in plant canopy was analyzed and the operation parameters were selected. Through the selected operation parameters, the control test against D. citri and P. citrella was carried out in the orchard from the spring shoot germination to autumn shoot mature period. The work quantity, time and labor consuming, dosage, water consumption, pesticide price and other expenses of the plant protection spraying operations by the UAV and artificial spraying were recorded in each time. After spraying, the insect number was investigated every 15 d.【Result】Taking into consideration of the operational efficiency and effective droplet deposition, UAV spraying under the fly height of 1.0 m and the flying speed of 1.7 m·s^-1 with open center tree-shape in the citrus orchards could get the better droplet penetration and distribution. The average droplet coverage rate reached 19.1%. Using these parameters, the UAV control test against D. citri and P. citrella was carried out in citrus orchard. Compared with manual spraying operation, there was no significant difference in control effect. However, the work efficiency of UAV spraying was 45 times of manual spraying, the total work cost of UAV spraying was 63.3% of manual spraying, and the amount of pesticide consumption was only about 10% of the manual spraying.【Conclusion】Based on the suitable spray parameters and tree structure, the control effect of UAV spray technology against D. citri and P. citrella can be obtained, and UAV spray technology is good for pesticide reduction, labor-saving and efficient cultivation management in the citrus orchard.

Key words: citrus orchard, unmanned aerial vehicle (UAV), spray technology, Diaphorina citri, Phyllocnistis citrella, control, comprehensive benefits