Efficacy improvement of a bioherbicidal fungus using a formulation-based approach

Authors: Boyette, Clyde; Hoagland, Robert; Stetina, Kenneth - Ken

Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2016
Publication Date: 11/28/2016
Citation: Boyette, C.D., Hoagland, R.E., Stetina, K.C. 2016. Efficacy improvement of a bioherbicidal fungus using a formulation-based approach. American Journal of Plant Sciences. 7:2349-2358.

Interpretive Summary: Eastern black nightshade (Solanum ptycanthum) is a problematic weed found throughout the eastern United States. Greenhouse experiments were conducted to compare the effects of an invert (water - in - oil) emulsion (IE) versus an oil - water (water + Tween 80) spore formulations of a bioherbicidal fungus [Colletotrichum coccodes (Strain NRRL 15547)] on dew period duration and dew delay for biocontrol of this weed. Dew periods of 4 to 12 h provided 10 to 40% control of eastern black nightshade plants 12 days after inoculation, when C. coccodes spores were applied in water + Tween 80 surfactant. But at least 16 h of dew was required to achieve ~95% plant mortality and when dew was delayed for 4 to 12 h, mortality was reduced with time (60 to 25%) in plants receiving this formulation. In contrast, the IE formulation was much more efficacious, providing 95 to 100% mortality after dew periods of 4 to 12 h; 95 to 90% weed mortality after dew delays of 4 to 12 h; and 60% mortality and 70% dry weight reductions of plants even in the absence of dew. Results demonstrate that formulating C. coccodes spores in an invert emulsion can greatly improve its bioherbicidal potential and provide strong implications that this formulation may also be applicable to some other bioherbicidal pathogens previously rejected for development because of inordinate dew requirements.

Technical 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 15547) 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.