Compatibility of a biological control agent with herbicides for control of invasive plant species

Kudzu, Pueraria montana var. lobata, is an exotic invasive weed that is difficult to control with available products and management practices. The fungal pathogen, Myrothecium verrucaria, is being developed as a bioherbicide for kudzu and other invasive vines. This biological control agent might be applied with conventional herbicides to improve the efficacy or spectrum of weed control. The survival of M. verrucaria was measured over time in simulated tank-mixes of commercial formulations of the herbicides: amniopyralid (Milestone*), metsulfuron (Escort XP), and fluroxypyr (Vista). The fungus was also grown in vitro in the presence of these herbicides to evaluate any growth inhibition. M. verrucaria was highly tolerant to all concentrations of amniopyralid and metsulfuron for up to two days in simulated tank-mixes, while mixtures with fluroxypyr resulted in a gradual loss of spore viability. The fungus grew on media supplemented with amniopyralid and metsulfuron with only small effects on the growth rate, but fluroxypyr caused growth inhibition. These studies provide insight for developing effective, integrated control strategies for kudzu.