Spotted knapweed, a recently declared noxious weed in Missouri, is spreading through the state at an alarming rate. Introduced to the state as early as 1963, it is now confirmed in 41 counties. Knapweed is an extremely aggressive invader capable of forming dense monocultures and displacing desirable livestock forage. It has very low palatability and cattle will avoid it. Knapweed readily infests roadsides and other disturbed sites and then spreads into adjacent undisturbed pastures and open forests. Spotted knapweed is most common in southwest and south central Missouri, however it has been recorded as far north as Putnam county on the Iowa state line and as far east as Ralls, Pike, Lincoln and Jefferson Counties.
In 2008 knapweed biocontrol insects were released for the first time by the Missouri Department of Transportation. These insects were the knapweed flower weevil and the knapweed root weevil. These weevils are the natural predators of knapweed in Europe and Asia. They feed only on knapweed and will starve to death before they feed on any native plants or crops.
The flower weevil feeds on developing knapweed seeds, while the root weevil attacks the plant’s roots, killing mature plants. Research by Montana State University has shown that when used together, these insects can reduce knapweed density by up to 99 percent over a period of several years.
A well-known biocontrol success in Missouri is the musk thistle weevil, which reduced that noxious weed throughout Missouri as well as other parts of the United States. The concept of biocontrol in knapweed is the same as that behind the thistle weevil, natural predators feeding on the plant in an effort to reduce its density and occurrence. As the knapweed population is reduced by the biocontrols, the insect’s population also declines until the plant and the insects come into equilibrium at a low population level. Biocontrols will never eradicate the weed, but they will significantly reduce its density and maintain it at a low level permanently.
University of Missouri Extension plans to make several releases of both the flower and root weevil in McDonald, Stone and Lawrence counties in the summer of 2009. These releases will spread and provide long term knapweed control in the areas where the releases are made.
Private landowners may apply for funding for biocontrol projects through the Natural Resource Conservation Service’s (NRCS) Environmental Quality Incentive Program (EQIP) and Wildlife Habitat Incentive Program (WHIP). Contact your local NRCS office for further information on applying for funding through these programs.
Bob Rich is with Weedbusters Biocontrol, Missoula, Mont.
