Weed Kills?

How harmful is Russian knapweed? Park volunteers are told to keep hands off.

Further proof that gardening can be hazardous to your health--or at least leave you digitally impaired--can be found in a nasty little weed that, along with its cousins, is threatening to take over the American West.

Like many of its fellow noxious weeds, Russian knapweed is particularly adept at killing off competitors and protecting itself from enemies. The plant concocts its own herbicide, which inhibits the growth of other plants nearby.

"These weeds push out native plant species that once provided homes, food, and shelter from predators," says Heather Poe, a park ranger at Roxborough State Park who is in charge of its noxious-weed program. "Some people, including the Division of Wildlife, say they do more harm to wildlife than human development. At least when people see a beautiful meadow bulldozed, they understand what that means to wildlife. With noxious weeds, it's more subtle, but just as devastating."

But it's not just other plants the noxious weeds affect. Studies have shown that Russian knapweed, when eaten in sufficient quantities, causes an impairment in the brains of horses that prevents them from being able to chew, says Poe.

So far there have not been any studies, she says, on the effect of the weed on wildlife that may eat it. "However," she adds, "there have been studies that show that a field that in the past supported 100 elk now can only support two."

And according to Weed Watch, a newsletter produced by the Colorado Weed Management Association, there has been at least one incident in which Russian knapweed may have harmed a person. In that case, which occurred about five years ago, a U.S. Forest Service employee in Idaho spent a day pulling up knapweed; skin on his hands was broken and came into contact with knapweed sap. The worker developed benign tumors and subsequently had to have two fingers amputated.

A follow-up article in last May's issue of Weed Watch written by Terry Cacek, integrated pest-management coordinator for the National Park Service in Fort Collins, pointed out that no scientific studies have been conducted to see whether contact with the plant really is harmful. "It is unlikely," Cacek wrote, "that exposure to knapweeds caused the tumors." But Cacek also wrote that no studies have been done to disprove a relationship. "Those who want to err on the side of caution," he wrote, "might want to avoid hand pulling, which generally is not an effective control."

Poe says the possibility of a link between health problems and the weed is enough to warrant warning volunteers with the park's "Weed Warriors Program."

"I certainly don't want to dismiss it," she says. "We tell all of our volunteers to wear gloves."

Noxious weeds, most of which are thought to have arrived in this country through agricultural products, are a huge issue, Poe says. "Whether or not this 'cancer' problem is borne out," she adds, "it's right at the top of every resource manager's list of priorities."

Scientists have known for years that Russian knapweed and other noxious weeds are moving in with enormous economic and environmental consequences. According to a report issued last week, scientists estimate that every day, 4,600 new acres of public land are infested with noxious weeds.

"Visually, try to imagine a fire that burns 4,600 acres each day," says Poe.
By state law, landowners are required to control noxious weeds, which include such plants as Canadian thistle and several varieties of knapweed. It's up to each county to determine which plants should be on the list and how it will try to control them.

 
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