Bacillus velezensis is an effective biocontrol bacterium, with its microbial pesticides showing promise in biological control. In this study, we optimized the medium and conditions for fermenting strain F0b, developed a wettable powder formulation, and assessed its efficacy against Botrytis cinerea. We screened carriers, wetting agents, dispersants, and UV protectants compatible with F0b, determining the optimal ratio and dosage. The best medium for F0b fermentation included rice flour (3.472%), ammonium chloride (4.898%), and disodium phosphate (1.871%). The ideal fermentation conditions were a 20% inoculum volume, 40 degrees C temperature, 80% sterile water, and a 72 h fermentation time, yielding a viable count of 1.33 x 1010 CFU/mL. The final formulation contained 54.7% Bacillus velezensis dried powder, 27.3% kaolinite carrier, 16% wetting agent (3:7 ratio of sodium dodecyl sulfate to sodium lignin sulfonate), and 2% ascorbic acid as a UV protectant. All quality indicators met national standards, with a viable bacteria concentration of 7 billion CFU/g. Field trials showed that the F0b wettable powder effectively controlled Botrytis cinerea, with a disease index significantly lower than the control group. Control efficacy ranged from 50.58% to 73.14% over 7 to 14 days, demonstrating the commercial potential of this formulation.
