Myrothecium verrucaria fungus: A bioherbicide and strategies to reduce its non-target risks

Studies were conducted on a fungi Myrothecium verrucaria (MV) strain, originally isolated from sicklepod (Senna obtusifolia L.), that exhibits bioherbicidal activity against kudzu [Pueraria lobata (Willd.) Ohwi] and several other weeds. Treatments of MV plus the surfactant Silwet L-77 caused 100% mortality or control to kudzu seedlings under greenhouse conditions, and 90% to 100% control of older kudzu plants in naturally-infested and experimental kudzu plots, respectively. MV caused greater reductions of kudzu plant biomass production at 30°C, compared to 20°C or 40°C, when tested in environmental chamber experiments. Responses of various non-target, young, woody plant species from several plant families to MV applications ranged from non-susceptible to moderately susceptible. Bioassays of MV on seed germination and early growth of sicklepod (Senna obtusifolia L.) and hemp sesbania [Sesbania exaltata (Raf.) Rybdb. Ex A.W. Hill] demonstrated that hemp sesbania was more sensitive than sicklepod to the fungus. Although MV possesses desirable bioherbicidal traits such as high virulence and the ability to control several species of weeds, this isolate also produces undesirable mycotoxins, i.e., trichothecenes. Research data are presented, as well as some discussion of future approaches to possibly reduce or eliminate these mycotoxins to develop a safe and efficacious bioherbicide.