Myrothecium verrucaria isolates and formulations as bioherbicide agents for kudzu

Abstract

The fungus Myrothecium verrucaria (MV) has previously been shown to have potential as a bioherbicide for kudzu (Pueraria lobata) control. It has also been shown that MV wild-type (MV-wt) often forms sectors, when grown on various nutrient media. Experiments compared MV-wt and MV sector efficacy when grown on agar or on rice grains. In greenhouse evaluations of sectors, applied as foliar sprays in water or in other formulations (corn oil, surfactant, and corn oil plus surfactant) for efficacy against kudzu seedlings, some sectors possessed bioherbicidal activity equal that of MV-wt, but others exhibited lower activity. Without a dew period, aqueous formulations of MV-wt, a yellow sector, and a white sector provided zero control, but all three isolates were active without a dew period when formulated in corn oil, Silwet L-77 surfactant, and in surfactant plus corn oil. Generally, the yellow sector was less effective than the other two isolates in any formulations, and the MV-wt and white sector provided approximately 100% mortality of the test plants. Dew (10 h) increased weed control to 100, 33, and 65%, respectively, for MV-wt, the yellow sector and the white sector. All isolates provided nearly 100% control in the oil and surfactant formulations with a dew period compared to treatments receiving no dew. Soil incorporation studies were also performed to compare MV-wt efficacy of preparations grown on agar versus growth on rice grains. Higher efficacies (1.75–3.3-fold increase) were obtained from rice grain preparations compared to preparations grown on agar, when preparations were incorporated at several rates into soil prior to planting. Cell-free extracts of the MV-rice cultures were also phytotoxic to kudzu seedlings up to the eight- to 10-leaf growth stage. Thus, formulation, growth media, and the application method are important determinants in the efficacy of MV and MV sectors on kudzu seedlings.