Biological control of kudzu (Pueraria lobata) with an isolate of Myrothecium verrucaria

An isolate of the fungus Myrothecium verrucaria (MV) was evaluated for biocontrol potential against kudzu (Pueraria lobata). In greenhouse tests, MV was highly virulent against kudzu in the absence of dew when conidia were formulated in 0.2% Silwet L-77 surfactant (SW). Inoculum concentrations >2 x 10(7) conidia ml(-1) were required to satisfactorily control plants in the third leaf stage and larger. In controlled environment experiments, kudzu mortality was greater at higher temperatures (25-40degreesC) than at lower temperatures (10-20degreesC), although pathogenesis and mortality occurred at all temperatures tested. In Weld tests, transplanted kudzu seedlings in the 2-3 leaf growth stage treated with MV at 2 x 10(7) conidia ml(-1) in 0.2% SW, exhibited leaf and stem necrosis within 24 h following inoculation, with mortality occurring within 96 h. After 7 days, 100% of inoculated kudzu plants were killed in plots treated with the fungus/surfactant mixtures. Similar results were observed in a naturally occurring kudzu population, where 100% control occurred within 14 days after inoculation with 2 x 10(7) conidia ml(-1) in 0.2% SW. In summary, MV effectively controlled kudzu in the absence of dew over a wide range of physical and environmental conditions and under Weld conditions. These results indicate that, when properly formulated, MV has potential as a valuable bioherbicide for controlling kudzu.