The scale insect pest is the main pest in agroforestry, causing varying degrees of damage to crops, fruit trees, ornamental plants, and forest trees. The fungus Cordyceps javanica IJID003 exhibits strong pathogenicity against scale insects, making it a promising candidate for the development of microbial pesticides. Research and development efforts focusing on its wettable powder formulation and the optimization of its production process are essential steps toward its industrialization and commercialization. The efforts are also crucial for promoting sustainable agricultural practices and achieving green pest management strategies. In this study, a single-factor test was employed to identify the optimal solid fermentation substrates and exogenous additives of strain IJID003. This research screened the optional carrier, wetting agent, dispersing agent and UV protective agent of the C. javanica by measuring the compatibility and its effective performance, which developed the wettable powder formula of the C. javanica preliminarily. The field efficacy of the C. javanica wettable powder was evaluated against female adults of Icerya jacobsoni on Michelia alba. The optimal spore-producing base substrate for C. javanica was barley. The best substrate formulation was a mixture of barley (7 parts) and wheat bran (1 part) by weight. The optimal exogenous additives included 1% glucose as a carbon source, 1% acid hydrolyzed casein as a nitrogen source, 2% potassium chloride as an inorganic salt, 1% glycine as an amino acid, and bee pupal body wall powder as a chitin source. The optimal formulation for the strain IJID003 wettable powder was 20% spore powder of IJID003, 1% wetting agent Morwet EFW, 5% dispersing agent Morwet D-450, 1% UV protectant CBS-X, and 73% carrier diatomaceous earth. Field trials demonstrated that a spore concentration of 6×10⁸ CFU/mL of C. javanica wettable powder effectively controlled female I. jacobsoni adults on M. alba, with an efficacy of 92.50% at 21 days post-inoculation. This efficacy was not significantly different from that of the control insecticide, a 4000-fold dilution of 25% thiamethoxam wettable powder, which achieved a control efficiency of 95.50%. In conclusion, the strain IJID003 wettable powder shows excellent potential for the green management of scale insects and holds significant promise as a sustainable alternative to chemical pesticides.