Nature Conservancy Magazine: Summer 2007 - The War on Weeds

SWAT stands for Strategic Weed Action Team. What it really means is two strong young guys grunting up and down hills with a 40-pound sprayer full of herbicides, zapping bad plants like Scotch thistle. The herbicides contain a blue dye so sprayers know where they’ve been.

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The War on Weeds

Fine Fat Maggots

The Conservancy’s tactics in the ground-weed war here are pretty straightforward: Contain them as much as possible, and when you find new outcrops, hit them hard. Pull no punches. Depending on circumstances, crews use herbicides, bio-weapons and plain old grunt labor.

Everything but the grunting has the potential for controversy. Yellow star thistle is common in its native lands but kept in check by the local insects that eat the thistle or its seeds. Now some of those bugs are munching silently in Hells Canyon.

Three types of weevils and two kinds of flies have been set free here. When the insects are doing their work well, they can kill 90 percent of the seeds in 90 percent of the pods in a patch of yellow star thistle.

The weevils lay eggs in seed pods, and those eggs emerge into fine fat maggots that devour thistle seeds inside the pod, before the seeds can spread. The weevils are cute little guys, with a proboscis like an anteater. But collectively these bugs have a scary sounding description — “biocontrol” — and you wonder, what’s to keep these critters from becoming some kind of “frankenbug”?

The short answer is, there’s no guarantee, says Atchison, whose job includes rounding up thousands of insects and disseminating them in new weed colonies.

But there is an incredibly high degree of certainty. The U.S. Department of Agriculture must approve the release of any insect new to the continent, and before it does so, the bugs undergo extensive tests in their native lands. If they display an appetite for any beneficial plants (be they non-native alfalfa and apple trees or native fescue and bunchgrass), they can’t come in.

In the case of yellow star thistle, all of the bugs used here are “food-specific” to that plant. If somehow all the thistles died, the bugs would starve. The weevils aren’t efficient enough to eat themselves out of a job any time soon. “When you’re talking biocontrols,” says Talsma, “you’re talking decades.” But they are effective at stemming expansions.

The insects are the primary tool in controlling big swaths of star thistle, collaring the plant’s advance. When smaller patches are found — say, a few acres — herbicides like Tordon, Milestone and Transline are the tools of choice.

Albeit, not the most appealing choice. Even Atchison is a little chary about it. “I don’t like chemicals in my body,” he says. “So I use all the protection I can.” He covers his eyes and hands. He wears long sleeves and long pants. He reads the labels and follows directions. “And we always use the lightest amount to take care of the weeds,” he says.

Chemicals aren’t cheap, Talsma explains. Spraying weeds from a helicopter costs $30 an acre. Zapping them from the back of an all-terrain vehicle costs about $80 an acre. Strapping on a backpack sprayer and puffing up and down the mountain costs about $120 an acre. And with so many acres at risk, those dollars add up (which is one reason why hopes are high for the bugs).

But the issue is more than money. Right now, exotic bugs and toxic chemicals are pretty much the only tools available to kill and contain invasive plants. While those tools have some shortcomings, without them, millions more acres of habitat would be lost. Vast food chains could be disrupted.

“Doing nothing has huge consequences,” Atchison says. “It’s just not an option.”

Yellow star thistle was a negligible presence in 1989, when the Conservancy first started working in Hells Canyon with the purchase of the China Garden Creek Ranch. Today, much of the ranch — most of which now belongs to the state of Idaho or the federal Bureau of Land Management — and the surrounding acreage is infested: about 100,000 acres of the 1.15-million-acre canyon. The Conservancy started its weed program here in 1999, then began the helicopter program in 2004. All those bright-yellow hillsides were painting a grim picture of the future.

Talsma says people often question him about the need to use chemicals and bugs. But for every skeptic, he says, “there’s somebody else who wonders why we didn’t start sooner.”

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