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Bugging Out

Tim Seastedt had a feeling about bugs.

Under the proper conditions -- and given enough time -- perhaps insects could succeed where farmers, ranchers and biologists have been failing for decades: at beating back diffuse knapweed, one of the nastiest, most invasive plants in the West. Five years after Seastedt and his beetles, weevils and gall flies first arrived at a 157-acre, weed-infested experimental site near Boulder, the results are in.

"Everything that we thought was going to work has, indeed, worked," says Seastedt, a professor of environmental, population and organismic biology at the University of Colorado. "What started as a 30 percent (knapweed) cover has fallen to well below 2 percent. And next year, we expect zero knapweed in the release site."

That's no small feat.

Diffuse knapweed, a member of the aster family, grows faster than many native plants in Colorado. Although scientists aren't sure when it first migrated to the United States from its home in southern Europe and the north central Ukraine, it appeared in Washington State as early as 1907, imported with an alfalfa shipment from the Caspian Sea.

The weed was first spotted in Colorado forty years ago, along a highway in Jefferson County. Today it occupies more than 83,000 acres along the Front Range alone, displacing native plants, destroying wildlife habitat and costing millions of dollars in lost crop productivity. In Boulder and Douglas counties, officials have called the weed's spread a "biological wildfire." To slow it down, authorities have resorted to herbicides, mowing machines, hungry goats, weed-pulling crews and even a few bug species. But the plant almost always returned.

Seastedt, an opponent of herbicides, decided to expand the bug arsenal ("Weed Whacker," August 9, 2001). Instead of using just one or two bugs to fight the weed, he enlisted five species to attack different parts of the plant simultaneously. In 1997, after receiving permission from Boulder County, he visited state agricultural offices, stocked up on free bugs and released them on a test site near Superior. For two years, not much happened -- other than the diffuse knapweed actually spreading over more ground. But in 1999, the weeds began to die. Today, knapweed rosettes on the experimental site have dropped from fifty per square meter in 1997 to one per square meter; seed production has plummeted from 5,000 per square meter to less than five; adult weeds have fallen from twenty per square meter to one. The bug population, meanwhile, has exploded from a few thousand to more than 200 million, moving off the original test site and decimating weeds on 70 percent of the surrounding land.

"There's no end to the questions," Seastedt says. "We're breaking new ground. We did this kind of blindly. We basically put five species of insects in there and left them undisturbed. We know if it works on our site. But we don't know if it will work everyplace else, which is why other folks need to try it."

So far, the City of Boulder and Arapahoe County have shown that they're willing. Even if many areas follow their lead, Seastedt doesn't believe that bugs alone will eradicate diffuse knapweed; used in combination with traditional methods, such as mowing, however, insects could certainly help keep it in check. And at a lower cost in both money and environmental risk than when herbicides are employed." There's no reason to believe that basic ecological principles functioning at our site will hold at a large number of sites," Seastedt says. "It should work for any comparable area on the Front Range. On the prairie, I have no reason to believe that they shouldn't be able to take on the knapweed."

 
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