Optimization of operating parameters for spraying microbial (Bacillus thuringiensis and Beauveria bassiana) based bio-pesticide solutions for foliar application

Exposure to mechanical stresses developed due to different components of spraying system may cause permanent damage to the microbes of bio-pesticide solutions. To achieve maximum effectiveness of spray application, proper selection of nozzle size and operating pressure is critical. Two different classes of bio-pesticides viz. bacterial-based Bacillus thuringiensis (BBP solution) and fungal-based Beauveria bassiana (FBP solution) were evaluated for spray application by three hollow cone nozzles (1.14, 2.35 and 3.56 mm in diameter) at four operating pressures (145, 245, 345 and 445 kPa). It was observed that viability of bio-pesticide solutions increases with decrease in operating pressure and increase in nozzle size. The nozzle orifice diameter and operating pressure of the spraying system were optimized to get desired application rate, volume median diameter (VMD) and coefficient of variation (CV) of spray for maximum microbial viability of bio-pesticide solutions. The optimized values of application rate (323.94-and 325.58 L ha−1), VMD (225.88 and 231.89 µm), CV (84.49 and 85.99%) and viability (6.63 × 106 and 6.06 × 106 cfu ml−1) were obtained for BBP and FBP solutions, respectively at nozzle orifice size of 3.56 mm and 145 kPa operating pressure.