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Weed Whacker!

Tim Seastedt takes no prisoners in the war against knapweed.

Tim Seastedt is at war.

His enemy is a drifter, voracious and cruel, striking fast and furiously. By 1997, it had already ravaged more than three million acres of rangeland in the West and fought off assaults by ravenous goats, chemical agents and flamethrowers.

Then Seastedt arrived on the scene, squaring off against the scourge on a 157-acre slice of prairie in Boulder County. His chances didn't look good: What could one lanky ecologist from the University of Colorado do to combat the dreaded Centaura diffusa? Study it to death?

Weed 'em and reap: Katie Suding (left), Kate LeJeune and Tim Seastedt in their anti-knapweed command post.Eric Lane heads the state's fight against weeds.
Weed 'em and reap: Katie Suding (left), Kate LeJeune and Tim Seastedt in their anti-knapweed command post.Eric Lane heads the state's fight against weeds.
Weed 'em and reap: Katie Suding (left), Kate LeJeune and Tim Seastedt in their anti-knapweed command post.
Anthony Camera
Weed 'em and reap: Katie Suding (left), Kate LeJeune and Tim Seastedt in their anti-knapweed command post.

But now, four years later, on a bright summer day, Seastedt strides through the pasture like an actor in an allergy-relief commercial, wearing a T-shirt bearing the words "Ecology With Attitude." Looking beyond the wildflowers, butterflies and meadowlarks, he spots signs of death and destruction. Weeds with stems stripped bare. Weeds with leaves eaten away. Weeds with seedheads decimated. Weeds starved for nutrients. Weeds pushed back by native grasses. Seastedt bends down on one knee and plucks a spindly forb from the damp soil.

"This guy's not going to make it," he says, examining the taproot, which has been split wide open by a burrowing weevil. "This is more than just good news. This is advanced good news!"

Seastedt casts aside the carcass and continues his stroll. Out on the prairie, armed with little more than bugs and fertilizer, he is winning the war against diffuse knapweed.


Colorado officials list 85 weeds they'd just as soon see wiped off the face of the earth -- plants that have overrun millions of acres of rangeland, displaced 10 percent of the state's native plants, destroyed habitat for bighorn sheep, elk and sage grouse, and caused $100 million in lost crop productivity annually. Diffuse knapweed ranks in the top five on this roster, behind only Canada thistle, field bindweed, Russian knapweed and leafy spurge. At last count, 83,000 acres along the Front Range alone were infested with diffuse knapweed, most of them in Boulder and Douglas counties.

Diffuse knapweed hails from southern Europe and the north central Ukraine; it's a member of the aster family, from the thistle tribe. Authorities aren't sure when it originally arrived in the United States, but in 1907 it was reported in Washington State, where it had been imported, along with alfalfa, from the Caspian Sea. It was first spotted in Colorado in 1962, along Highway 124 in Jefferson County. Here it found all the comforts of home: flat, well-drained, light-textured, nitrogen-rich soils; a climate similar to that of Europe; few range fires; even fewer knapweed-eating insects. The weed wasted no time nestling into gopher holes, vacant lots, train tracks, cattle pastures and roadsides, where it proceeded to be fruitful and multiply. By the mid-'90s, it was out of control.

Once established, diffuse knapweed employs an array of physiological weapons to make sure it remains a fixture on the landscape. It grows a single tap root that sinks deeper than the roots of shallower competing plants, allowing it to suck up more water and nutrients. If a neighbor does tap into the knapweed's supplies, the weed secretes a bitter chemical called cnicin, which inhibits that neighbor's ability to germinate, grow seeds and absorb nutrients. The same chemical also makes knapweed taste really bad to most grazing animals and bugs.

Diffuse knapweed grows faster and more furiously than many native grassland plants, reaching as high as forty inches. The weed can survive two years in one spot, then reproduce and live another two years through its offspring. Knapweed can also function as an annual or biennial and, depending on the availability of nutrients, germinate throughout an entire growing season.

A single plant can produce up to 900 seeds each year. These seeds are hidden inside urn-shaped stickers ideal for gradual dispersion over long distances. The stickerheads attach easily to animal hides, blue jeans and tractor tires, hitchhiking where no weed has gone before. When a plant dies, it simply snaps off at the stem and becomes a tumbling, seed-releasing machine.

Once diffuse knapweed enters the picture, within several years, native plants are bullied, poisoned and overwhelmed. If the weed is left unchecked, it will dominate its surroundings.

In Boulder and Douglas counties, the spread of diffuse knapweed has been compared to a "biological wildfire." The priority has been to stop it -- quickly. So authorities have fired up mowing machines, and road crews have sliced, diced and minced the weed to death. But only temporarily. With so many seeds out there, it quickly returns. It also adapts, growing thicker, wider and beyond the reach of mower blades.

So authorities have hosted weed-pulling parties. They've enlisted prison labor, drafted sullen teenagers and slipped on gloves themselves. But seeds slip through fingers. And weed crews, no matter how enthusiastic, can't pluck every stickerhead from the soil.

So authorities have unleashed goats, which gobble the weeds nicely. But as with mowing, the weeds return within a year. And after a few bellyfuls of knapweed, goats tend to lose their appetites.

For many weed managers, the weapon of choice has become an herbicide called Tordon 22K, which Seastedt says essentially causes the weed to oxidize itself, or "exhale itself to death." Tordon 22K is sprayed from helicopters, tanker trucks and hand-held containers; one application can wipe out knapweed for two years.

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