Compatibility of Metarhizium anisopliae and Beauveria bassiana with insecticides and fungicides used in macadamia production in Australia

Abstract Background Integrating fungal biocontrol agents into crop protection programs dominated by synthetic pesticides is an important first step towards developing an integrated pest management (IPM) program; however, their successful integration relies on an understanding of how their performance may be impacted by the remaining agrochemicals deployed for managing other pests and diseases. In this study we tested 10 formulated pesticides used in macadamia production at different concentrations to determine their effects on the germination, mycelial growth and sporulation of Metarhizium anisopliae and Beauveria bassiana in vitro . Further tests with laboratory‐grade actives of the noncompatible pesticides were conducted to determine whether any antagonistic effects were caused by the active constituent or by formulation additives. Results At their registered concentrations, formulated trichlorfon, acephate and indoxacarb were compatible with M. anisopliae , whereas B. bassiana showed compatibility with formulated trichlorfon, acephate, indoxacarb, sulfoxaflor and spinetoram. Bioassays using laboratory‐grade active constituents indicated that the adverse impact of formulated beta‐cyfluthrin on both fungal species and that of formulated methidathion on B. bassiana is probably due to components of the emulsifiable concentrate formulations rather than their active constituents. Diazinon was the only insecticidal active that showed high toxicity to both fungal species. The two fungicides, carbendazim and pyraclostrobin, were toxic to both fungal species at all tested concentrations. Conclusion Our results identify which pesticides used on macadamias in Australia are compatible and incompatible with entomopathogenic fungi. Future studies on pesticide degradation rates will help define the spray intervals required to eliminate these adverse effects.