Weed Whacker!

Tim Seastedt takes no prisoners in the war against knapweed.

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."

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


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 minutus seedhead weevils, which lay eggs on flowers, eat blossoms and gobble up seeds. Two species, seedhead gall flies called Urophora affinus and 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.

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