Abstract: [Objective] The aim of this paper is to make progress in the areas of droplet size spectra, viability and infectivity delivery options and control effect, and it will contribute to overcoming the impediments and increasing use of biopesticides.[Method] A rotary disk atomizer for biopesticide was developed, and an air-assisted system was also designed to improve the atmospheric effects. The influences of biopesticide atomizer structure (disk diameter, oblique angle and teeth number), operational parameters (flow rate, spinning speed and wind speed of air-assisted system), and spraying downstream range on atomization performance and biopesticide application efficacy was tested. The spraying was repeated with water sensitive cards placed on the artificial plant leaf surface to determine the distribution of spray coverage rate. Characteristics of mean droplet size of spray produced by rotary disk atomizers were experimentally investigated. A Sympatec laser diffraction analyzer was used to measure the droplet size of water spray in the downstream distance along the spray trajectory. Effects of different structure parameters and various operating conditions on the mean diameter had been studied. The volume median diameter (VMD) was used to represent the generated spray droplet sizes.[Result] 1) The teeth number and oblique angle had no significant influence on the droplet size, but the disk diameter,flow rate, spinning speed and the spraying downstream distance were related to the droplet size. It was also found that VMD increases as the downstream distance, and liquid flow rate increase. Meanwhile, a decrease of spinning speed and disk diameter result in an increasing VMD. 2) A regression model for volume median diameters (VMD) prediction including four independent, non-correlated variables (rotary disk diameter, spinning speed, liquid flow rate and the spraying downstream distance) was established. Furthermore, the model's goodness-of-fit was also assessed to prove model fitness and feasibility. 3) The result of water sensitive cards placed on the artificial plant leaf surface showed that air-assisted system increase the spray coverage rate due to due to the fact that droplets with stronger penetrability by the aid of air-assisted system. Facing the wind direction, the distribution of spray coverage rate in front layer is much higher than that in rear layer. 4)This paper also discussed the viability and infectivity of air-assisted rotary disk atomizer by spraying beauveria bassiana. The result showed that the main effects of four experimental factors on the viability and infectivity of biopesticide were ordered by wind speed > rotary disk diameter > spinning speed > liquid flow rate > oblique angle > teeth number.[Conclusion] The rotary disk atomizers can increase the spray coverage rate and enhance the control effect by air-assisted system. VMD can be correlated with the rotary disk diameter, spinning speed, liquid flow rate and the spraying downstream distance. The regression model provided a VMD evaluation approach, and it was important in the interpretation of droplet size for different measuring distance, operation techniques and rotary disk structures.[Result] from this paper provided a case study showing how to spray biopesticide to treat plant pests and diseases effectively by setting optimal parameter.

Key words: forest disease and pest control, biopesticide, air-assisted, rotary disk atomizer, downstream range, viability and infectivity of biopesticide