Toxicity of Post-Emergent Herbicides on Entomopathogenic Fungi Used in the Management of Corn Leafhopper: In Vitro and In Vivo Assessments

This is the first study to assess the physicochemical and biological compatibility of herbicides used in corn crops with entomopathogenic fungi used in the management of Dalbulus maidis in Brazil. The biological index was employed to ascertain the in vitro compatibility of the herbicides with pure spores (not formulated) of tested fungal isolates (Esalq-1296 of Cordyceps javanica and IBCB66 and Simbi BB15 of Beauveria bassiana ). The results indicated a significant interaction between herbicides and fungal isolates when colony diameter and colony-forming units (CFU) were considered. Furthermore, changes in physicochemical characteristics were observed in some mixtures of herbicides and mycoinsecticides tested. The number of CFU was significantly reduced as the exposure time increased in the mixtures containing all the herbicides tested. In general, the Esalq-1296 isolate of C. javanica , formulated in a suspension concentrate (Octane ® ), proved to be more sensitive to the herbicides studied. In vivo bioassays demonstrated that, despite the synergistic effect of the binary mixtures of herbicides and mycoinsecticides on D. maidis mortality, the presence of the herbicide in the mixtures prevented the extrusion of entomopathogens from cadavers; therefore, caution is recommended when combining mycoinsecticides and post-emergent herbicides in tank mixtures aiming to manage D. maidis .