Evaluation of spraying efficacy of the air-assisted orchard sprayer in modern dwarfing-rootstock apple orchard

Abstract: 【Objective】Combining good application technology with advanced application machinery, optimizing parameters such as droplet size, spray volume and traction speed can give full play to the performance of application instruments, improve the utilization rate of pesticides, and achieve precise prevention and control. However, the normative evaluation of the application efficacy of modern machinery, and the reference of the measure adjustment and the equipment improvement are lacking. This research aimed to investigate the spraying effect of air-assisted sprayer, optimize application parameters by comparing and analyzing the changes of droplet characteristics, droplet deposition distribution and ground loss rate of 3WF-1000 air-assisted tower sprayer in the apple orchard with wide planting rows and dwarfing rootstocks, so as to provide theoretical reference for pesticide application“reducing quantity and increasing efficiency”in modern dwarfing-rootstock apple orchards.【Methods】Five-year-old Yanfu 3 apple cultivar with spindle-shaped canopy was used as experimental material. The spacing between plants and rows were (1.25-1.50) m × 4.5 m, respectively. The volume median diameter (VMD), droplet density and droplet coverage of the 3WF-1000 air-assisted tower sprayer were tested by water-sensitive paper, and the foliar deposition and ground deposition were tested by tracer agent allura red. A row with the length of 50 m was selected as the test plot and three discontinuous apple trees were randomly selected as sampling points. In order to investigate the droplet characteristics, the canopy was vertically divided into upper (2.0 m), middle (1.5 m) and lower (1.0 m) layers, and five points were selected as distribution sample points in the east, south, west, north and middle of each canopy. A paper clip was used to fix each water-sensitive paper with the detection face down. To investigate the ground loss rate, a dish was placed in each of four directions (east, south, west and north), 30 cm away from the trunk. 20 g of allura red was fully dissolved in 100 L of water and added to the sprayer at the traction speeds of 1.16 m·s -1 (4.18 km·h-1 ) or 1.77 m·s -1 (6.37 km·h-1 ). The water-sensitive paper was put into a plastic bag and brought back to the laboratory. After scanning, the droplet size, droplet density and coverage were measured by Image J software. In order to test the foliar deposition, three leaves were collected at each sampling point. After measuring the leaf area, each leaf was washed with 5 mL distilled water for 10 min, the absorption of the washing solution at 501 nm was determined, and the concentration of allura red was calculated according to the standard curve. The dried dishes were added with 10 mL distilled water, and shaken at 100 r·min-1 for 5 min. The absorption of the washing solution at 501 nm was measured and the concentration of allura red was calculated.【Results】The droplet characteristics of the sprayer at different traction speeds were significantly different in the five-year-old modern dwarfingrootstock and wide-row apple orchard. Compared with the traction speed of 1.16 m·s - 1 (4.18 km· h- 1 ), the droplet coverage and VMD at 1.77 m ·s - 1 (6.37 km · h- 1 ) decreased from 62.19% and 142.67 μm to 57.03% and 131.67 μm, and the droplet density (141.72 points· cm- 2 ) increased to 179.86 points· cm- 2 . The average foliar deposition, ground deposition and utilization rate at the speed of 1.77 m · s - 1 were 0.24 μg · cm- 2 , 0.55 μg · cm- 2 and 47.1%, respectively, and were both higher than those of 1.16 m ·s - 1 (0.22 μg·cm-2 , 0.43 μg·cm-2 , and 43.7%, respectively). The droplet parameters of the sprayer in the east, south, west, north and middle of the tree were also different at two traction speeds. When the traction speed was 1.77 m·s -1 , the droplet coverage in the east, west, south and north was lower than that at the traction speed of 1.16 m ·s - 1 , but it was opposite in the middle canopy, which was significantly higher than that at the traction speed of 1.16 m·s -1 (p＜0.05). The droplet particle size at the traction speed of 1.77 m·s -1 was lower than that at 1.16 m·s -1 in all 5 directions, and the south direction had a significant difference (p＜0.05). The droplet density in the east, west, north and middle of the tree at the traction speed of 1.77 m·s -1 was higher than that at 1.16 m·s -1 , while the droplet density in the south was slightly lower. The distribution of foliar deposition at the two traction speeds of the sprayer was in such a descending order: the upper canopy > the middle canopy ≥ the lower canopy of the tree, and the deposition amount in the outer of the tree was higher than that in the inner at the height of the middle and low canopy. At the traction speed of 1.77 m·s -1 , the deposition amount in the inner and outer canopy of the middle and lower canopy (deposition ratio of inner to outer was 0.73 and 0.65) was higher than that at the traction speed of 1.16 m ·s - 1 (deposition ratio of inner to outer was 0.72 and 0.64). However, there was no significant difference in the amount of liquid deposited in the upper, middle and lower canopy of the tree (p＜0.05).【Conclusion】The droplet characteristics of the 3WF-1000 air-assisted sprayer at two traction speeds (1.16 m·s -1 and 1.77 m·s -1 ) could meet the requirements of disease and pest control in modern dwarfing-rootstock apple orchards. The better pesticide utilization rate was observed with the sprayer at the traction speed of 1.77 m·s -1 , but the soil loss rate would increase as well.