Effects of herbicides on in vitro vegetative growth and sporulation of entomopathogenic fungi

Abstract

Four commonly used herbicides were evaluated at two different temperatures and three concentrations (10X, 1X and 0.1X, where X = recommended field rate) for compatibility in vitro with the entomopathogenic fungi Conidiobolus thromboides, C. coronatus, Beauveria bassiana, Metarhizium anisopliae, Paecilomyces farinosus and Verticillium lecanii. The effects of the herbicides on radial growth during the whole test period (14 days at 25 °C and 24 days at 15 °C), and intensity of sporulation were quantified. Generally, phenmedipham plus desmedipham (1:1), metolachlor, and chloridazon had pronounced adverse effects on all fungi. The 1X rate of these three herbicides either totally impaired the development of the fungi at both temperatures or strongly inhibited the growth at 25 °C, as in B. bassiana, M. anisopliae and V. lecanii. The 0.1X rate of these herbicides usually resulted in fungistasis, which was not expressed in subcultures of the fungi on herbicide-free agar. The fourth herbicide, lenacil, killed C. thromboides when tested at 25 °C at the 1X and 10X rates. At the 0.1X rate, lenacil had a temporary stimulatory effect on the development of the test fungi. In all other fungus-herbicide concentration-temperature combinations, lenacil had a temporary, reversible inhibitory effect. Of the herbicides tested, lenacil, which showed a less adverse effect in the tests, is probably compatible with most entomopathogenic fungi in the field. This is not the case, however, with phenmedipham plus desmedipham, metolachlor, and chloridazon, which are strongly antagonistic.