Weeds Could Meet Their Match in a Novel Bioherbicide

Annual morningglories and other broad-leaved weeds could meet their match in a novel bioherbicide that includes weak or nonvirulent fungi and an oil emulsion, Agricultural Research Service (ARS) studies suggest.

Use of the bioherbicide could offer a nature-based alternative to conventional chemical controls--and the risks associated with applying them, such as drift beyond crop fields and groundwater contamination--note ARS plant pathologist Norman Schaad and retired ARS researcher Shaw-Ming Yang.

One bioherbicide ingredient is the saprophytic fungus Myrothecium verrucaria. In nature, it survives by absorbing nutrients from decaying plant matter. When mixed with oil, however, it can kill many common dicot weed species, including annual morningglories, bermudagrass, pigweed and bindweed.

In early greenhouse studies, Yang showed that oil serves as both an emulsifier that retains moisture and a synergist that enables the fungus to kill weeds. Neither M. verrucaria or oil alone will damage plants, so natural movement of the fungus to crops or other nontarget plants isn’t likely.

In test plots in Maryland, Louisiana, Mexico and France, the fungus killed or damaged the weeds as effectively as the herbicides atrazine and 2,4-D. In June 2000 trials on Houma, La., sugarcane plots, about 95 percent of smallflower morningglory plants sprayed with the fungus died 4 days later, versus 100 percent for those treated with atrazine. Rex Millhollon, a collaborating scientist at ARS’ Sugarcane Research Station in Houma, conducted the trials.

The team began experimenting with M. verrucaria in 1997. In 1998, they received a patent covering use of weak or nonvirulent fungi in combination with an adjuvant and oil emulsion as a broad-spectrum bioherbicide. The technology is now available for licensing. Before commercialization is possible, however, scientists must first determine whether this strain of the fungus produces metabolic byproducts called trichothecenes that are dangerous to humans and other animals. Dana Berner and assistant Larry Paxton are investigating the possibility at ARS' Foreign Disease-Weed Science Laboratory in Fort Detrick, Md.

ARS is the U.S. Department of Agriculture's principal scientific research arm.