Weed Wars
DB: This is Earth and Sky. Some brightly-colored wildflowers blooming in a mountain meadow are on the government’s “most-wanted” list.
JB: Leafy spurge, Russian knapweed and yellow toadflax are among the plants classified by the U.S. government as “noxious weeds.” They arrived here from Europe or Asia – some brought by the first European settlers centuries ago. Since then, the plants have been moving west.
DB: Here in North America, these plants aren’t bothered by the diseases, insects, and herbivores found on their native turf. So the weeds spread – and spread. They crowd out native plants. Mule deer and elk can’t feed in a meadow where musk thistle and houndstongue have replaced native grasses. Russian knapweed can be poisonous to horses.
JB: But weeding out the weeds is tough – especially in the West’s many backcountry areas. In some places, “biological control organisms” from the weeds’ native homes are being introduced. Hikers are being told to groom their dogs and clean the soles of their boots. And wilderness rangers are trained to recognize noxious weeds – to help squelch a small invasion – before having to reclaim acres of land that have gone to weeds.
DB: Today’s show was made possible by the National Fish and Wildlife Foundation, in cooperation with the U.S. Forest Service. We’re Block and Byrd for Earth and Sky.
The following individual(s) were interviewed for today’s show. Our thanks to:
Mark Tucker
Range Management Specialist
USDA Forest Service
San Juan National Forest
Dolores, CO
Craig Goodell
Assistant Fire Management Officer
Columbia Ranger District
San Juan National Forest
Bayfield, Colorado
The following articles and web sites provided information relevant to this script:
Website of the San Juan National Forest (USDA Forest Service)
Web site of the Colorado Weed Management Association
Author’s notes by Cynthia Berger:
Not all those pretty flowers are natural, warns rangeland management specialist Mark Tucker. The brightly colored wildflowers in a mountain meadow or streamside wetland may include such noxious weed species as leafy spurge; diffuse, spotted, and Russian knapweed; Canadian, musk, yellow star, and Scotch thistles; field bindweed; cheatgrass; houndstongue; and yellow and Dalmatian toadflax (there are many others).
The exact definition of a “weed” is open debate; one team of Arizona researchers say a weed is a plant that interferes with the management objectives of a given area of land at the given time. Many of the plants that are considered “noxious weeds” in the American West originated in the Middle East, spread to Europe along trade routes, and were brought to this continent by European settlers inadvertently, mixed in with grain and agricultural seeds, mixed with feed for livestock, mixed with the ballast of ships, and hidden in the soil surrounding potted plants. A few species now considered weeds were cherished ornamental garden plants in Europe but escaped from gardens here and, finding little competition from native plants, have come to be regarded as pests. Once they reached the New World, weeds spread inland along roads and railroad beds; in this century they’ve been helped along the way by long-distance trucking and by the movement of heavy construction and logging equipment. According to the Bureau of Land Management, noxious weeds consume 4,600 acres a day (i.e. 4,600 football fields’ worth of land) on western public lands. The Colorado Weed Management Association estimates that of the States 1,300 native plant species, about 10 percent have been displaced by non-native weeds.
In the last ten years we’ve seen weeds encroaching more and more into wilderness areas, says Craig Goodell, now a fire management officer but formerly a range management technician working on weed control in the San Juan National Forest.
“We’re in containment mode, not eradication mode”, says Tucker, also of the San Juan National Forest, where an estimated 5 percent of the forest – 1.8 million acres – are infested with noxious weeds. “We try to stop weed infestations while they’re small”, notes Goodell. “If they get big in these remote areas, we really can’t deal with them.” Many of the plants considered to be noxious weeds have life habits that make them hard to eradicate. Many produce seeds by the thousands, and often, these seeds are very tough. For example, the seeds of field bindweed remain viable-able to sprout-for up to forty years. Other species are stellar competitors. The roots of a single leafy spurge plant can extend for as much as thirty feet, making it all but impossible to eliminate the plant by uprooting it. Russian knaps weed and certain other weeds release chemicals from their roots that keep other vegetation from growing in the immediate area. The Forest Service takes a multifaceted approach to weed control. In areas in the San Juan National Forest where logging occurs, logging equipment must be cleaned before it is moved to new sites in the forest, to reduce the risk that weed seeds will be transported into a new area. Because windborn weed seeds find favorable conditions and sprout in the disturbed soil that’s present in a logged-over area, land managers go into a recently logged area with targeted herbicides to knock the weeds back before they set new seeds and spread even more. And herbicide applications are also targeted along trails and at trailheads, to reduce the risk that hikers will inadvertently pick up and spread weed seeds. In addition to spot use of herbicides, low-impact biological control is an option for some weed species. For example, musk thistle is being controlled in the San Juan Forest by two kinds of weevils; one eats the seed heads while the other chows down on the leaves. And in one fragile wetland area where herbicides aren’t an option, flea beetles are being used to control leafy spurge. In other locations, some noxious weeds can be controlled by targeted livestock grazing practices. Sheep in particular will often feed selectively on certain noxious weeds.
Additional Teacher Resources
South Dakota Department of Agriculture: Integrated Weed Management Options for Noxious Weeds
A brief report on the status of noxious weeds in South Dakota. This report includes sections covering: What is a noxious weed?; Why control noxious weeds?; Integrated weed management; Biological Controls
