Abstract: In order to develop a new microbial fungicide with stability and control effect against powdery mildew, Bacillus subtilis YN2014090 was used as an active ingredient. By adding dispersants, wetting agents, thickeners, UV protective agents, preservatives, etc., the agents were mixed in the corresponding proportions to prepare a suspension of YN2014090, and the number of viable bacteria reached 3.2×10¹⁰ cfu/mL. The optimum ratio of wetting and dispersing agent was screened by single factor screening aid and orthogonal test. The final formula was determined as:YN2014090 bacteria powder 15% (3.2×10¹⁰ cfu/mL), xanthan gum 2.2%, dispersing agent EMA 8%, 600# 12%, D425 2.2%, OP-10 2.2%, Tween 20 1.2%, PEG600 1.2%, urea 0.3%, and methyl p-hydroxybenzoate 0.12%. The pH value of the prepared suspension agent was between 8.20 and 8.30, the fineness (<10 μm) pass rate was greater than 95%, the long-lasting foam amount (after 1min) was less than 38mL, the residue mass fraction after pouring was less than 5%, and the residue quality after washing was less than 0.4%. The control efficacy reached 94.21% on tomato powdery mildew 11 d after 2 sprays, indicating that the suspension concentrate has a good potential to control tomato powdery mildew.

Key words: dispersants, wetting agent, suspension concentrate, tomato powdery mildew, control