Efficacy Improvement of a Bioherbicidal Fungus Using a Formulation-Based Approach

Abstract

Greenhouse experiments were conducted to determine the effects of an invert (water-in-oil) emulsion (IE) on dew period duration and dew delay of Colletotrichum coccodes for biocontrol of the problematic weed, eastern black nightshade ( Solanum ptycanthum ). Dew periods of 4, 8, or 12 h provided 10%, 25%, and 40% control of eastern black nightshade plants, respectively, when C. coccodes (Strain NRRL 15,547) spores were applied in water + Tween 80 surfactant 12 days after inoculation, but a minimum of 16 h of dew was required to achieve ~95% plant mortality. In contrast, at these same intervals of dew, 95%, 100% and 100% mortality occurred, respectively, when fungal spores were formulated in the IE. Even in the absence of dew, 60% mortality and 70% dry weight reductions of plants was achieved with the fungus/IE formulation Delaying dew by 2 h after inoculation did not significantly reduce weed control or plant dry weight reductions when plants were inoculated with the fungus either in the aqueous or in the IE formulation. However, when dew was delayed for 4, 8, or 12 h, only 60%, 50%, and 25% mortality, respectively, of plants receiving the aqueous spore treatment occurred. In contrast, 95%, 90%, and 90% weed mortality occurred after the same dew delays of plants receiving the fungus/ IE treatments. These results demonstrate that formulating C. coccodes spores in an invert emulsion greatly improves the bioherbicidal potential of this fungus. Furthermore, results suggest that this formulation may render pathogens previously rejected for development as bioherbicides due to restrictive dew requirements more efficacious for use in controlling their target weeds.