Bio-pesticides are currently applied using existing spraying systems, with spray droplet size being a crucial factor influencing canopy penetration, material carrying capacity and the viability of micro-organisms. Hydraulic nozzles atomize spray liquids into droplets ranging from 5 to over 1000 μm in diameter. For effective foliar application, the 100-300 μm droplet size range is recommended a guideline typically followed for chemical-based sprays and now applied to microbial-based bio-pesticide solutions. This study aimed to validate the droplet size distribution for microbial bio-pesticide solutions within this optimal range. Two bio-pesticides, bacterial-based Bacillus thuringiensis (BBP) and fungal-based Beauveria bassiana (FBP), were evaluated. Experiments were conducted using three liquid solutions (water-only, BBP, and FBP), three types of hydraulic nozzles (HCN/PA, HCN/PB, HCN/PC), and four operating pressures (145, 245, 345, and 445 kPa). Droplet size distributions were measured across five size ranges: less than 100 μm, 100-200 μm, 200-300 μm, 300-400 μm, and more than 400 μm using a droplet size analyzer. The focus of the analysis was on the 100-300 μm range, as this is the most effective for crop protection. Nozzle type, operating pressure, and spray solution significantly influenced droplet size distribution (p < 0.001); although reductions of 3.22% for Bacillus thuringiensis and 6.22% for Beauveria bassiana were observed in the biologically optimal 100-300 μm range relative to water, the resulting droplet spectra remained suitable for effective microbial bio-pesticide application. This demonstrates the suitability of bio-pesticide solutions for foliar application using conventional spraying systems, optimizing droplet size for effective pest control.
Kumar et al. (2026) studied this question.