Weed Whacker!

Tim Seastedt takes no prisoners in the war against knapweed.

"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."

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.


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."

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