Assessment of Insecticide Compatibility with Metarhizium (Nomuraea) rileyi for Fall Armyworm (Spodoptera frugiperda) Management in Maize

The mycelial growth of Metarhizium rileyi, an entomopathogenic fungus, was evaluated in media treated with various insecticides and their inhibitory effects on fungal growth. The effects of insecticides Thiodicarb 75 WP, Spinetoram 11.7 SC, Emamectin benzoate 5 SG, Chlorantraniliprole 18.5 SC, Novaluron 5.25 + Emamectin benzoate 0.9 SC, and Chlorantraniliprole 9.3 + Lambda-cyhalothrin 4.6 ZC were tested at different concentrations (50%, 75% and 100% recommended concentration)1/2, 3/4, and full recommended concentrations, Recommended Concentration). Observations at 7, 14, and 21 days after inoculation revealed significant differences in fungal growth compared to the control. Thiodicarb 75 WP showed minimal inhibition, with the lowest growth inhibition (12.73%) at 3/4th RC, indicating high compatibility with M. rileyi. Emamectin benzoate 5 SG also showed low inhibition (0.61-24.85%) at various concentrations, supporting robust fungal growth. In contrast, Spinetoram 11.7 SC exhibited the highest growth inhibition (60.61-69.70%), particularly at full RC. The study concludes that lower concentrations of certain insecticides, particularly Thiodicarb, Emamectin benzoate, and Chlorantraniliprole, have minimal inhibitory effects on M. rileyi, while higher concentrations of Spinetoram and Novaluron + Emamectin benzoate had shown significant inhibition. These findings suggest that compatibility between M. rileyi and insecticides is concentration-dependent, highlighting the importance of formulation selection for integrated pest management strategies.