Abstract:

Objective: China has been using the cross-spraying method of air and ground to control forest pests. Stereoscopic spraying chemical has been adopted in the forestry pests control which apply pesticide both on the ground and in the air. Due to greater human awareness of environmental conservation and public health, pests and diseases control requires accurate, efficient, scientific, and reasonable operation according to the actual conditions. A wide variety of choices and decisions must be made by applicators to result in a successful pesticide application. Examples of these choices include proper adjuvant mixture and spray equipment (e.g. nozzle type and orifice size) and application technique (e.g. spraying pressure) selection while also considering environmental influences such as wind speed. Droplet size is one of the most important factors affecting spray application, efficacy, drift and spray performance optimization. Method: A laser diffraction technique in wind tunnel was used to provide complimentary information on droplet size distribution and spectra. Droplet size was determined by application conditions (nozzle type, spraying pressure, operation condition and wind speed), and tank mixing physical properties were affected by the carriers (water or oil) and adjuvants (drift retardant, surfactant and wetting agent). These sprays were atomized using ground nozzles and aerial nozzles placed in a wind tunnel and the droplet spectra measured via a laser diffraction instrument. Result: Experimental results showed that the VMD decreased with the increase of the spray pressure and decrease of nozzle's orifice size. It was also showed by tests that when spraying 41A liquid as drift retardant, VMD produced by nozzles increased compared with water as solution in the wind tunnel, and all the nozzles' RS value increased, the spectrum category changed. When the CHEMWET100 as wetting agent and LI700 as surfactant, VMD produced by import nozzles and domestic nozzle reduced lightly and the spectrum category remained the same. Droplet size sprayed by CP nozzles could be changed both by orifice size and deflector angle. Increasing the deflector angle produced smaller droplets, e.g., 30° produced smaller droplets than those of 0°. Meanwhile, using a downward deflection of 30 degree might have improved relative RS of droplet sizes for CP nozzle. Conclusion: Spray mix composition and adjuvant could have a large effect on droplet size and spray performance criteria. During aerial application, in order to reduce the drift of airborne droplets, appropriate pesticide additives (such as drift retardant 41A) should be added to increase the droplet size and improve their adhesion. During ground application, appropriate pesticide additives (such as surfactant LI700) should be added to reduce the droplet size and enhance the deposition rate in order to ensure the coverage area and canopy penetration. For the leaves of trees with a thick waxy layer, the surface might be difficult to be wetted by the pesticide solution. When spraying pesticides on these targets, the wetting agent CHEMWET should be used to increase the wettability and adhesion of the pesticide solution to the target surface.

Key words: forestry pests, chemical application on the ground, chemical application in the air, pesticide's adjuvant, nozzle, droplet size