Submitted to: Weed Biology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2006
Publication Date: 2/2/2007
Citation: Boyette, C.D., Hoagland, R.E., Weaver, M.A. 2007. Biocontrol efficacy of Colletotrichum truncatum for hemp sesbania (Sesbania exaltata) is enhanced with unrefined corn oil and surfactant. Weed Biology and Management. 7:70-76. doi:10.1111/j.1445-6664.2006.00230.x. Interpretive Summary: Hemp sesbania (Sesbania exaltata) is a problematic weed in soybeans throughout much of the southeastern U.S. An isolate of the fungal pathogen Colletotrichum truncatum has shown promise as a bioherbicide for controlling this weed. An emulsion formulation consisting of unrefined corn oil and a surfactant (Silwet L-77) stimulated spore germination and infection of hemp sesabania in greenhouse and laboratory conditions. Infection by the fungus typically requies dew, and the fungus has increased ability to infect in the absence of dew in the emulsion formulation. In three years of field experiments, a single application of formulated fungus controlled hemp sesbania in soybeans an average of 95%. Soybean yields were significantly higher in plots where weeds were effectively controlled. The results in this report indicate that, with superior formulations, Colletotrichum truncatum can be a very effective bioherbicide for controlling hemp sesbania.
Technical Abstract: In greenhouse and field experiments, an oil – in – water emulsion of unrefined corn oil and Silwet L-77 increased the biological weed control efficacy of Colletotrichum truncatum (Schw.) Andrus & Moore for control of the weed hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill]. The surfactant - corn oil emulsion stimulated germination and appressoria formation in vivo and in vitro and delayed the need for dew. We hypothesize that the corn oil protected the conidia from desiccation during the dew - free period and the surfactant stimulated spore germination and appressoria formation. In field experiments conducted over three years, a single application of a 50% (v / v) unrefined corn oil tank mixture containing 0.2% (v / v) Silwet L-77 surfactant controlled hemp sesbania in soybeans an average of 95%. Aqueous fungal suspensions or adjuvants alone did not affect or control hemp sesbania. Soybean yields were significantly higher in plots where weeds were effectively controlled. These results suggest that formulating C. truncatum in unrefined corn oil and surfactant greatly increases infectivity and the biocontrol potential of this pathogen.