Knapweed May Hold The Key to Creating Effective, Natural Herbicide

By KATHERINE VOGT Associated Press Writer

DENVER (AP) -- An invasive weed that has taken over vast swaths of grazing land in the West may hold the key to creating an effective, natural herbicide.

A Colorado State University study found that a chemical compound secreted from the roots of spotted knapweed is toxic to surrounding plants and has potential to wipe out other unwanted weeds.

``This is an herbicide that is as potent as a commercial chemical but it comes from a natural plant,'' said study author Jorge Vivanco, an assistant professor of horticulture biotechnology at CSU. ``It's considered an environmentally friendly herbicide.''

Vivanco's research _ and a separate study at the University of Colorado in which bugs stopped the spread of diffuse knapweed _ are among the latest efforts to find natural ways of controlling invasive plant species that have bedeviled farmers and ranchers for centuries.

``I think we're see an emerging emphasis on nonchemical alternative techniques in weed management,'' said Eric Lane, the state weed coordinator for Colorado.

``It's exciting to see the results (of these studies) because it's the sort of thing that will stimulate others to conduct more research in an area of weed science that is not overrun with research.''

At least three knapweed species are found in Colorado, and forms of the invasive weed have taken over millions of acres in the West. Knapweed species are capable of wiping out all other surrounding plants, effectively ruining grazing lands. They have few predators because they are nonnative species.

Originally from eastern Europe and western Asia, the most common knapweed species in the West are believed to have arrived in the late 1800s in contaminated crop seed or possibly discarded soil from ships.

Common forms feature tiny white or purple flowers on spindly, leafed green stalks.

Two years ago, Vivanco read about a knapweed species that invades and colonizes areas by secreting a toxic compound into the soil through its roots.

His team tried to become the first to isolate the chemical from spotted knapweed _ a feat complicated by the complex jumble of contaminants, microbes and chemicals found in soil.

The team grew spotted knapweed plants in flasks in the lab. The roots were submerged in a water-based solution while the plant floated on top.

The plants secreted the toxic chemical compound into the liquid, making it easier for the researchers to isolate each compound in it.

They found nearly 30 compounds, including two forms of catechin. One type had antibacterial properties and the other had a toxic effect on other plants.

The researchers found that spraying the toxic form of catechin on plants or adding it to soil was as effective against some weeds as common synthetic herbicides, typically killing the plants within a week.

Vivanco said no one previously knew about catechin's toxic effect on plants.

His findings were published in April in the journal Plant Physiology.

Because there is no evidence that catechin is toxic to humans or animals, Vivanco hopes it will eventually be fast-tracked for approval by the Environmental Protection Agency.

CSU has licensed the ``catechin'' technology patent to a company. Vivanco hopes to see it on the market in two or three years.

Ragan Callaway, an associate professor of biology at the University of Montana and a plant ecologist who specializes in invasive weeds, said Vivanco's research is exciting but should be carefully studied.

``Just because it's produced organically doesn't mean it won't kill you. On the other hand, I think that because Jorge is trying to use natural processes to control how plants interact with each other is fantastic,'' Callaway said.

Vivanco said the discovery has several potential applications as an herbicide. In reduced concentrations the chemical only kills select plants while sparing others. That could allow farmers to protect a crop while killing a weed. Or it could be used as a preventative agent by mixing it with soil before weeds can even emerge.               

 At the University of Colorado in Boulder, researchers are studying a different kind of natural knapweed fighter: bugs. CU ecology professor Tim Seastedt and his researchers found what they believe is a way to stop the spread of diffuse knapweed _ at least along the Front Range.

Testing his theory on a parcel of open space in Boulder County, Seastedt released a combination of several insects into a field of diffuse knapweed in 1997.

After several tries, the researchers found the right combination of insects to eat and kill the plants. Seastedt said his particular bug combination _ two picture wing flies, a seed-head weevil and two beetles _ had not been used on diffuse knapweed.

By 2000, some restored prairie had emerged. By 2002, swaths of restored land had extended beyond the original 160-acre plot.

Seastedt said the insects attack all systems on the plant.

``The combined stress seems to do the plants in,'' he said. ``We threw the kitchen sink at them. We used everything that has been available.''

Though bio controls sometimes threaten native plants, Seastedt said his insects seem uninterested in native species.

He said his team will continue to research which conditions are necessary for the bio control to work. The preliminary findings will be published in Weed Science in March.