Compatibility of selected herbicides with entomopathogenic fungus Beauveria bassiana (Bals.) Vuill

The in vitro effect of five commonly used herbicides viz., pyridate, fluazifop-P-butyl, foramsulfuron, tembotrione and Smetolachlor on mycelial growth of entomopathogenic fungus Beauveria bassiana (ATCC 74040) was evaluated each at different concentrations: 100, 75, 50, 25, 12.5, 6.25 and 0% of recommended field application rate on PDA agar plates at 15 and 25°C. The herbicides tested were classified in 1-4 scoring categories based on reduction in mycelial growth: 1 = harmless (<25% reduction), 2 = slightly harmful (25-50%), 3 = moderately harmful (51-75%), harmful (>75%) in toxicity tests. All the five herbicides had fungistatic effect to B. bassiana at varying intensities depending on their concentrations in medium. The present study showed that B. bassiana is very sensitive to the herbicides tested, particularly at recommended as well as lower field dosage. The selected herbicides foramsulfuron, tembotrione and S-metolachlor have strong fungistatic effect on mycelial growth (> 75% inhibition) at 15 °C and concentrations from 50 to 100%. Foramsulfuron has fungicidal effect at 100 % concentration. Foramsulfuron, tembotrione and S-metolachlor were less inhibitory at 25 than at 15 °C, but the temperature had no influence on reduction of mycelial growth at pyridate and fluazifop-P-butyl. Of the herbicides tested, pyridate and fluazifop-P-butyl showed less adverse effects and are probably compatible with B. bassiana in the field. However, extensive field studies complemented by parallel laboratory experiments should consider assessing the interaction between selected herbicides and B. bassiana isolates to evaluate their ecological impact in cropped environments.