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May 21st, 2001

INSTAAR researchers receive grant to study noxious weed

Researchers at the University of Colorado at Boulder have received a $280,000 grant to help unlock the mystery of how diffuse knapweed, a noxious weed that has infested more than 80,000 acres along the Front Range and 3.2 million acres in the West, has become dominant in the prairies around Boulder.

The three-year study, funded by the United States Department of Agriculture, will test a series of questions about how knapweed responds to changes in soil chemistry and how it chemically modifies soil for its own benefit, according to CU-Boulder Professor Tim Seastedt, who will be working on the study with CU-Boulder researchers Kate LeJeune and Katie Suding.

"Essentially we are looking for a way to remove diffuse knapweed's ability to dominate other plants," Seastedt said. "Once we have found how knapweed obtains and sustains its dominance over native plants, we can work on a cost-effective, environmentally friendly way to control it."

The researchers are members of the environmental, population and organismic biology department and the Institute of Arctic and Alpine Research at CU-Boulder.

Historically, perennial grasses dominated the prairies around Boulder and the Front Range because they were able to hoard nutrients in the soil, like nitrogen, keeping a low nutrient availability in the soil, Seastedt said. "These native perennial grasses basically out-competed the other plants by keeping the nitrogen to themselves."

However, the researchers believe that increased nutrient availability in the soil from long-term overgrazing, atmospheric nitrogen deposition or absence of wildfires has led to the knapweed's success. Over time, the nutrient buildup has erased the advantage the native perennials once held and tipped the balance in favor of weeds like diffuse knapweed.

Part of the study includes experiments to find out if diffuse knapweed can still dominate a grassland system if there is low nutrient availability in the soil. The researchers don't think it can.

Evidence suggests the weed's competitive edge is making phosphorus unavailable to other plants, thus preventing native species from obtaining adequate nutrients and moisture, Seastedt said.

"Diffuse knapweed may practice subterranean chemical warfare by secreting chemicals that interfere with the ability of other plants to take up food," he said.

"Over the next three years we hope to find an economical way to reduce phosphorus in the soil, and thus take away this weed's advantage," he said. "If we add something to the soil that makes phosphorus unavailable to the weed, we may find its Achilles heel."

Seastedt said it is possible that the research will give the native plants a leg up on diffuse knapweed, but that it is highly unlikely that the weed will completely disappear in Colorado or other infested areas.

"We are going to have to learn to live with knapweed, but hopefully we can turn the tables on it," he said.

Weed control agents have used herbicides, mowing, grazing and various other biological methods to control the spread of diffuse knapweed. The noxious weed has infested large areas of the West over the past 30 years and is extremely difficult to control, because each plant produces numerous seed heads that can be spread by wind, water, animals, people and vehicles. The plants also become tumbleweeds when they die, allowing them to travel long distances dispersing seeds as they go.

Diffuse knapweed is in the sunflower family, is native to Europe and Asia and is commonly found in Romania, Yugoslavia, Turkey, Greece and other countries. The weeds, which stand about two feet tall and produce white flowers, have little nutritive value to animals like deer and cows because they are hard to digest and can be toxic if eaten in large amounts. Grazing animals often skip over the weeds, putting other plants at an even greater disadvantage. Other areas affected by diffuse knapweed include Montana, Washington, Idaho and Canada.

The research is part of a larger project that looks at how biological controls such as insects and vertebrate grazers and soil resources can be manipulated to the detriment of the weed and to the benefit of the native species.