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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.
Eric Lane heads the state's fight against weeds.
Anthony Camera
Eric Lane heads the state's fight against weeds.

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.

But Tordon 22K is expensive: about $75 per gallon wholesale, or about twice as much as Curtail, a competing herbicide. It is also controversial. Although officials contend that if Tordon 22K is properly diluted, at about one pint per acre, it won't hurt people, animals or most native grasses, anti-herbicide groups have fought long and hard to stop its use. They say the chemical is indeed dangerous to people and animals. Not only does it kill knapweed, but it destroys some twenty other leafy plants as well. And while Tordon does kill knapweed for two years, it's as temporary as hand-pulling, goats or mowers. Because of its large seed production, the weed eventually returns, and authorities must spray again.

Under the 1991 Undesirable Plant Management Act, every county is required to develop a plan to identify and handle noxious weeds. And so county officials wrote rules, formed weed-management boards, coordinated strategies and set about to educate the public. But they've had trouble enforcing the rules, coordinating the strategies and educating the public. So the act was amended in 1996 and the position of state weed manager created.

Today, however, Eric Lane, Colorado's weed manager, grudgingly draws this conclusion: "Uninfested areas are still becoming infested. In that respect, with this one species, we are slowly losing the battle."


Enter Tim Seastedt.

A 52-year-old Nebraska native with a suntanned face, bristle-brush mustache and vocabulary loaded with phrases like "biomass" and "stem density," Seastedt started his scientific career as a zoologist in Montana, tagging grizzly bears. But he longed to "solve big-picture questions" about "whole-level landscapes," and after spending two years as a Peace Corps worker in Tonga, "waiting for Nixon to solve Vietnam," he returned to the U.S. and became an ecologist. He studied in Alaska and Georgia and Kansas, where he specialized in grasslands, "trying to understand why dominant species are dominant." He arrived in Colorado in 1990 and became a professor of environmental population and organic biology at the University of Colorado.

In 1996, at the height of the battle over herbicides in Boulder County, Citizens for Alternatives to Toxins in Boulder tried to enlist Seastedt's help. He turned them down, but when they asked again a year later, Seastedt offered to review the scientific reports for Boulder County's weed plan.

"But there were no reports," Seastedt recalls. "There was no science justifying their management program. As an ecologist, I was used to doing science-based, ecosystem land management. The first ground rule is you obtain data. I thought, 'If they're doing these things without data, there might be a problem.'"

Although Seastedt wasn't officially affiliated with the anti-toxics group, he sympathized with them. When fighting weeds, employing herbicides is like using an anvil to hammer a nail.

"My advocacy has always been the least toxic approach," he says. "In my mind, using that stuff as a routine tool was just unacceptable."

So he started doing some investigating of his own. And he realized that while the chemicals were killing a lot of weeds, "the weeds are just going to come back. We need something more sustainable."

His first thought was bugs.

In Colorado, insects have been used to fight diffuse knapweed for more than a decade, with decidedly mixed results. But when Seastedt visited places such as Walker Ranch, where bugs have been deployed on and off for years, he found that at least one species, a weevil, had enjoyed some successes before being hindered by herbicide spraying, weed pulling or mowing. So despite the popular consensus that bugs had failed, Seastedt was encouraged.

"I saw evidence that biocontrols could work, given enough time," he says.

After getting the green light from Boulder County to conduct his experiment on 157 acres near Superior, he visited state agricultural offices and loaded up on free bugs. But instead of releasing one or two species, which had been the approach in the past, Seastedt decided to use five bugs to attack different parts of the weed simultaneously. If one bug died or moved along, another would take over.

So in the summer of 1997, Seastedt released fifty root-boring weevils named Cyphocleonus, which feed upon infant knapweeds and lay eggs on their roots. Then he released 300 beetles named Sphenoptera jugoslavica,which attack the roots, stunt growth, reduce flower production and kill rosettes. Next, he released 200 Larinus minutusseedhead weevils, which lay eggs on flowers, eat blossoms and gobble up seeds. Two species, seedhead gall flies called Urophora affinusand U. quadrifasciata,had already been released; they lay eggs on flowers and sap the weed's energy.

Then he waited.

For two years, nothing seemed to happen. In fact, he remembers, the weeds got bigger and covered more ground. But in the summer of 1999, Seastedt noticed a bug boom, an exponential growth of insects "straight out of an ecology textbook." Then weeds became stunted. Then weeds stopped producing as many seeds. Then they stopped spreading as rapidly.

When he studied the results this summer, even Seastedt was surprised: Rosettes have dropped from 50 per square meter in 1997 to three; seed production has been slashed from 5,000 per square meter to below 100; adult weeds have fallen from twenty per square meter to less than five. And weeds that appear healthy are little more than insect reservoirs, serving as both a home and a food source. By next summer, he says, those weeds will be producing new bugs instead of new knapweeds. And if that happens, the insect population could soar beyond twenty million -- enough to supply knapweed-eating bugs to the entire Front Range.

"Look at this," Seastedt says, yanking a droopy weed from the pasture. "What we're getting are these wimpy little plants. Roots have been hit. Seedheads are empty. They've been defoliated. Larinus has done its damage. The gull flies have been doing their thing. There's just nothing here to support the final product. Next year, I'm not even sure there will be knapweeds here."

With the knapweed in full retreat, native plants will be free to take their place. Some already have.

"When we started, you could hardly find June grass here," Seastedt says. "And when you did, it was just these tiny clumps. Now it's all over. The recovery has just been spectacular. Next year, I predict 90 percent restored prairie. And the 10 percent of knapweed that is here will be grazed to the ground."


Even if the bugs are successful, Seastedt believes that the ultimate way to beat diffuse knapweed is to understand why it has flourished in Colorado -- and then reverse the process.

His team is trying to do just that on the land outside Superior.

Here is Seastedt's theory. Diffuse knapweed has been able to thrive in Colorado because, among other things, changes in the soil over the past 150 years gave the weed a competitive edge. First, the rangeland has been grazed continuously, and plants that might have offered competition have been repeatedly nibbled away. Second, fires have been limited, and fires cleanse the soil of nutrients that weeds love, including nitrogen. In fact, scientists have discovered that one of the fastest ways to turn healthy grasslands into weed fields is to add nitrogen. And nitrogen, as it turns out, is the third factor: Nitrogen levels have been rising steadily in the soil, in part because of increases in atmospheric deposits.

Seastedt wonders: Can scientists reverse the process? Can they tinker with soil chemistry and restore rangeland to its pre-knapweed condition? And if they succeed, will it blunt the weed's competitive edge? Will it bring back healthy native plants and grasses?

To find out, Seastedt and researchers Katie Suding and Kate LeJeune cordoned off certain plots and added nitrogen. The plants -- particularly pepper grass, which grew in thick bunches loved it. But diffuse knapweed stayed more or less unchanged.

Interesting, the researchers thought. Perhaps nitrogen wasn't so vital to knapweed after all. Perhaps another nutrient determined whether the weed would live or die. In other parts of the world, like the tropics, phosphorus is a key nutrient; perhaps knapweed needed phosphorus.

So they added phosphorus, and while other plants stayed more or less unchanged, diffuse knapweed bulked up like a linebacker on steroids.

Interesting, the researchers thought. Diffuse knapweed liked phosphorus; perhaps phosphorus would prove knapweed's Achilles heel.

So they tinkered some more, adding phosphorus and nitrogen, removing phosphorus and nitrogen, pulling knapweed from some plots and leaving knapweed in others. Although it's too early to tell what the results of this summer's experiments will be, they think they're on the right track. In May, they were awarded a $280,000 federal grant. Now if they can find the right mix of phosphorus, nitrogen or some other nutrient, they might be able to tip the balance away from knapweed and toward native plants and grasses.

"Once native grasses are happy and healthy again, we think they are capable of greatly reducing knapweed," Seastedt says.


Margaret Paget manages 300 acres of open land in Wheat Ridge with "considerable" knapweed. She has mowed, sprayed and lopped off seedheads with dandelion pickers, yet the weed thrives.

Paget toured Seastedt's research site last month. "I was impressed," she says. "There are a lot of tools out there, and this looks like a good one. From my standpoint, trying to control these weeds in a way that does not involve herbicides is a good alternative. If I could get his bugs, I'd use them."

Jerry Neri is a certified organic farmer and herbicide opponent. He's been fighting knapweed for years, too. "I've seen the site every year for the past few years, and it's gotten incredibly better," he says of Seastedt's experiment. "It's not only cheap and natural, but it's also achieving the ultimate goal, which is to control these things in an environmentally responsible way. There's always going to be a little knapweed, but those five insects pretty much kick ass."

Jonathan Rife is the weed inspector for Douglas County, where diffuse knapweed has infested thousands of acres. He also sees promise in Seastedt's work, but he wonders whether the bugs will work in different soil and weather conditions. In Douglas County, he has robust weeds that look like "a different subspecies" from the weeds in Boulder. And he points out that although state officials have tried various combinations of insects, they have reported "very disappointing results."

State weed manager Lane is also cautious. "It looks like one beetle has taken quite well, but it's too soon to tell what the end result would be," he says. "People tend to fixate on one particular tool -- some on herbicides, some on hand-pulling, some on biological controls. But it's our experience that no one tool is going to be the magic bullet. We're really glad Tim's work is focusing on a species that could have significant payoffs, but we wouldn't expect the same for other species. We've tried a lot of insects on a lot of different species, and it's safe to say that a majority have not provided appreciable controls. Tim's research is helping explore the possibilities, but it may be more the exception than the rule. It looks promising, but it's not a sure thing by any stretch of the imagination."

Nevertheless, Lane adds, in one way, Sea-stedt's bugs have worked too well. Not only have they ravaged the knapweed, but they've also infested an area that was previously bug-free. "That's unfortunate," Lane says. "We don't have something to objectively compare it to."

Cindy Owsley, Boulder County weed-management coordinator, remembers when four species of knapweed-eating insects were released on a particularly sensitive acre of Walker Ranch back in the '80s. Ten years later, that one acre had become a hundred infested acres. "Now we have a significant problem," Owsley says. "And as a result, we have to use more herbicide."

Eight years ago, Owsley used bugs to control musk thistle. Although the bugs worked, they worked slowly, she says. When landowners gazed out their windows at what appeared to be healthy weeds, they complained -- and when she asked them to be patient, they complained even louder.

"I've been the subject of ridicule in that area ever since," she says. "If people look outside and see diffuse knapweed growing, and we say we're controlling it with insects only, it's going to be the same scenario. That's intolerable from a neighboring landowner's perspective. We feel a strong responsibility to be good neighbors."

According to Ron Stewart, a Boulder County commissioner, the commissioners support Seastedt's efforts. That's why they loaned him the 157 acres in the first place. But weed managers do not have the luxury of waiting five years for insects to become established, he says; the county cannot risk losing more land to diffuse knapweed. Which is why insects will probably continue to be "one more tool in the tool box" alongside herbicides.

"I've looked at his site. I've looked at the site where we have sprayed. And there's a lot less knapweed on the area we sprayed," Stewart says. "His project, to this point at least, does not prove you can do weed control without using multiple tools. We believe biocontrols have a very significant place in weed management, but I don't think he has proven that he can do it yet without the use of herbicides. "

Seastedt has heard that criticism before.

He welcomes it.

"Hey," he says, "I live and die on data. If I had failed with this, I was prepared to tell the world. But so far, it looks pretty good."

Seastedt realizes that insects alone will not stop diffuse knapweed, and he knows bugs do not work in all circumstances and in all conditions, including alongside roadways. But if used with other methods, such as hand-pulling or mowing, insects can keep the weed in check -- and with less damage to the environment and the pocketbook.

"For this species, I'm completely convinced that insects are less risky than chemicals," he says.

After four years, Seastedt's getting closer to the answer. And with weed warriors having fought the knapweed war for so long, that's "major good news," he says. "We've tried something that had been out there but not been tried in this way before. So far, we've potentially been lucky."

Seastedt doesn't worry that the imported beetles, weevils and flies will devour other plants. The feeding and reproductive habits of the five bugs are tied to the unique characteristics of knapweed, he says. But just in case, his researchers are keeping a close eye on the bugs. They've even sprayed knapweed juice on other plants to entice them.

"So far, the bugs are behaving themselves," Seastedt says. "I suppose anything is possible. Mutation happens. But there are 5,000 native insects that have the same potential to mutate. All we're doing is adding four more species that may do something weird, like suddenly decide to eat asphalt, but that's such a low probability that I don't think it's much of a risk. All these guys will probably do is go in search of diffuse knapweed until they die trying to find it. The worst-case scenario is that they'll munch on some distant relative of knapweed, like an aster. Anything beyond that is pure science fiction."

No matter how successful his experiments, Seastedt doesn't believe diffuse knapweed will ever be completely eradicated. In fact, he doesn't think weed managers should even try. At best, they can only hope to reduce the weed to a level that allows native plants and grasses to return.

"What I'd like to see is a prairie dominated by the vegetation we want to be there: native plants given the maximum potential to express diversity," Seastedt says. "If that means 1 or 2 percent cover by diffuse knapweed, that wouldn't bother me at all. It would be just like the dandelion. And if we can get knapweed to be like a dandelion, then we've done our job."

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