Controlling Kudzu With Naturally Occurring Fungus

By one estimate, kudzu spreads at the rate of 150,000 acres annually, easily outpacing the use of herbicide spraying and mowing, as well increasing the costs of these controls by $6 million annually.

But in Stoneville, Miss., ARS plant pathologist Doug Boyette and colleagues are testing a fungus named Myrothecium verrucaria, which infects kudzu with an astonishing speed of its own. In fact, the fungus works so quickly that kudzu plants sprayed with it in the morning start showing signs of damage by mid-afternoon, according to Boyette, with the ARS Southern Weed Science Research Unit in Stoneville.

He first began working with M. verrucaria in 1998, when a Louisiana Tech University scientist furnished him with isolates from diseased sicklepod specimens. In greenhouse experiments, spray formulations killed 100 percent of kudzu seedlings and 90 to 100 percent of older plants in outdoor trials. Myrothecium also worked its anti-kudzu magic under a wide range of conditions, including the absence of dew.

Additionally, host-range tests in 2005 showed that Myrothecium caused little or no injury to many of the woody plants known to occur in kudzu-infested habitats, including oak, cedar, pine, hickory, pecan, sassafras and blackberry.

A few companies expressed interest, but only if the fungus' production of toxins called trichothecenes could be reduced or stopped. Boyette's group examined several approaches, settling on a method of growing Myrothecium in a fermenter on a liquid diet instead of a solid one. Not only did this stop trichothecene production or reduce it to acceptable levels, the method also extended the fungus' shelf life and potency under field conditions.

Besides kudzu, Myrothecium also showed potential as a pre-emergence bioherbicide, controlling purslane and spurge in transplanted tomatoes.