Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/30/2007
Publication Date: 12/5/2007
Citation: Hoagland, R.E., Boyette, C.D., Abbas, H.K. 2007. Myrothecium verrucaria Isolates and Formulations as Bioherbicide Agents for Kudzu. Biocontrol Science and Technology. 17(7):721-731. Interpretive Summary: Since the introduction of kudzu (Pueraria lobata) into the U.S. (late 1800's) for erosion control and as forage, it now inundates millions of hectares in many eastern, southern and some mid-western states. In 1998, Congress declared kudzu a noxious weed. Although some synthetic herbicides control kudzu, repeated applications over several years are required, and such herbicides can damage non-target plants in its habitat. Greenhouse/field tests indicate the fungal pathogen Myrothecium verrucaria (MV) has bioherbicidal activity on kudzu without detrimental effects to many trees and shrubs. MV forms spontaneous mutants (sectors) when grown on various media. MV preparations grown on agar versus growth on rice grains indicated a 1.75 ' 3.3-fold higher efficacy of the rice grain preparations incorporated in soil at several rates prior to planting. Some sectors possessed bioherbicidal activity equal to that of MV, but some exhibited lower activity. Without a dew period, aqueous formulations of MV and two sectors, provided zero control, but activity of all three isolates was increased substantially when formulated in corn oil, Silwet L-77 surfactant, and surfactant + corn oil. Overall results indicate that formulation, growth media, and application method are important considerations for the development of MV (and/or MV sectors) as a commercial bioherbicide for kudzu.
Technical Abstract: The fungus Myrothecium verrucaria (MV) has previously been shown to have potential as a bioherbicide for kudzu (Pueraria lobata) control. With the goal of improving, and more completely characterizing this bioherbicide, further tests in our laboratory showed 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. 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, indicated some sectors possessed bioherbicidal activity equal that of MV-wt, but some 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 about 100% mortality of the test plants. Dew (10 hours), 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. Studies comparing MV-wt efficacy of preparations grown on agar versus growth on rice grains indicated higher efficacies (1.75 ' 3.3-fold increase) of the rice grain preparations when incorporated at several rates into soil prior to planting. Bioherbicidal activity of ground MV-wt-rice grains showed that cell-free extracts of the MV-rice culture was also phytotoxic to kudzu seedlings up to the 8 ' 10 leaf growth stage. Thus, formulation, growth media, and application method are important in the efficacy of MV and MV sectors on kudzu seedlings.