Open Space Invaders

Open Space Invaders

Noxious weeds crowd out native plants, ruin rangeland, and cost farmers and ranchers millions. How Montana is fighting back. By David Stalling

This story is featured in Montana Outdoors July-August 2011 issue

If the commonly used term “war on weeds” seems overly dramatic, consider this: Noxious weeds today infest more than 130 million acres of the United States.

Each year they overrun an additional 1.7 million acres, invading an estimated 6 square miles of Bureau of Land Management (BLM) and U.S. Forest Service (USFS) lands every day. Weeds have infested more than 7 million acres in national parks, including Glacier and Yellowstone. Harmful invasive plants are a major scourge of agriculture, which declared the “war.” Each year noxious weeds cost Montana producers $100 million in control expenses and crop production losses, according to the Montana State University (MSU) Extension Service.

Invasives also devastate native vegetation, in some cases reducing entire biologically diverse plant communities to large tracts of just one or two dominant species. And by crowding out indigenous grasses and forbs that wildlife eat, noxious weeds reduce the amount of forage available for deer, elk, and pronghorn.

“Noxious weeds” is a legal term state and federal agencies use to denote exotic plants posing serious threats to agriculture, wild­life, and native plant communities. Many weeds reach this continent as seeds inadvertently carried in grain shipments. Others are brought by well-meaning folks to grace gardens or help control erosion. Once here, plants and their seeds hitch rides aboard birds, big game animals, wool pants, horses, trains, and the tires of trucks and all-terrain vehicles. Some simply ride with the wind or float along rivers.

One of the most invasive exotic plants is spotted knapweed, which arrived in North America from central Europe in 1883, mixed in with shipments of alfalfa or soil used as ship ballast. Knapweed has since crowded out native plants on 2.8 million acres in Montana, thriving on soil disturbed by logging, grazing, flooding, or fire. By sending down stout taproots, knapweed gets the jump on other plants with its early spring growth and snatches up space, sun, water, and nutrients. Each plant produces more than 1,000 seeds annually, creating knapseed stands of up to two million plants per acre. According to the Forest Service, such densities can reduce the total amount of native grasses and forbs by as much as 90 percent.

Making matters worse, native plants have a tough time growing back even after knapweed has been eliminated. Documenting the first scientific evidence of a plant using an offensive chemical weapon, researchers at the University of Montana and Colorado State University recently verified that knapweed releases a substance called “catechin” that destroys roots of surrounding vegetation.

The U. S. government recognizes roughly 4,000 exotic plants as “pests.” Of those, 90 are federal noxious weeds, and dozens more are listed as noxious by various states. The BLM refers to exotic weeds as “A Growing Pain,” the U.S. Department of Agriculture calls them “Silent Invaders,” and The Nature Conservancy created “The Dirty Dozen” list of “America’s Most Wanted: A Rogue’s Gallery of Invasive Plants and Animals.” In an article for Sierra magazine, writer Robert Devine coined the term “botanical barbarians.”

Barbarians, indeed. Noxious weeds have a competitive edge over native plants because their natural predators—mammals, birds, insects, and fungi—don’t live here. Just as deer and elk proliferate in the absence of predation—human or otherwise—noxious weeds multiply on lands where few natural enemies exist. In Montana, aggressive species such as leafy spurge, spotted knapweed, and Dalmatian toadflax take over prairies, wetlands, sagebrush steppes, mountain parklands, and riverbanks. Though research on the ecological effects is spotty, scientists know that invasive plants greatly reduce biological diversity in native plant communities. And because the roots of weeds hold less soil than native vegetation roots, erosion increases dramatically where invasives such as knapweed dominate.

opsoil sloughs into streams and fouls spawning and rearing habitat critical to trout and other fish. An MSU study published in 1989 found that surface runoff and sediment loss were nearly three times higher on sites dominated by spotted knapweed than on those where native bunchgrass predominated. In a Wyoming study, sites dominated by native prairie bunchgrass lost only 12.5 pounds of soil per acre in a simulated thunderstorm, while sites overrun by spotted knapweed lost more than 125 pounds per acre.

Noxious weeds also threaten native plant communities in national parks. During one three-year period in Glacier, spotted knapweed nearly eliminated seven rare or uncommon native species. Yellowstone reports widespread infestations of Dalmatian toadflax and Canada thistle.

The few studies on how noxious weeds affect wildlife raise concerns among conservation agencies and organizations. Researchers at the University of South Dakota found that deer and bison used areas dominated by leafy spurge far less than similar uninfested sites. A study in the early 1990s by Mike Thompson, now FWP regional wildlife manager in Missoula, found that dense stands of spotted knapweed in native bunchgrass sites reduced available winter forage for elk. “We can’t go so far as to conclude that noxious weeds reduce elk numbers in Montana,” Thompson says. “That’s because in much of the state we’re already managing populations below the land’s biological carrying capacity, in order to reduce wildlife depredation problems on private land. But weed infestations definitely make a difference in elk distribution. If you have more weeds on public lands, elk could move to other property where there are fewer weeds.”

Nonprofit conservation groups are concerned, too. The Nature Conservancy and the Rocky Mountain Elk Foundation have warned of the threat noxious weeds pose to wildlife and native plant communities.

Then there’s aesthetics. Though noxious weeds sprout colorful flowers, people who value native plant communities wince at the sight of knapweed over­taking shortgrass prairie or leafy spurge spilling over riverbanks. And few sights are more discouraging to dog owners than their Brittany, springer spaniel, or golden retriever covered in houndstongue or burdock seed.

“It’s easy to get depressed about noxious weeds,” says Jim Olivarez, a retired weed program manager for the USFS Northern Region. “But I try to look at it this way: About 95 percent of our public land is not affected by weeds, and we can keep it that way. I refuse to let these plants dominate the landscape. These lands are national treasures, and we need to protect them.”

Montana has been fighting noxious plants for more than a century. The state legislature passed its first laws to control weeds as early as 1895. Yet by the late 1920s, invasive exotic vegetation had spread to every county in the state. Today, 32 species infest 7.6 million acres of Montana.

In 2000 Montana developed a comprehensive, state­wide noxious weed management plan. Its goal is to boost existing weed management and promote new, ecological ways of controlling weeds. The plan notes that noxious weeds are controlled by identifying ways the plants are spread, educating land­owners and others on how to limit spread and prevent introductions, and conducting plant inventories and research. Weeds are killed using herbicides, fire, hand pulling, and insect predators (known as biocontrols.)

Dave Burch, state weed coordinator with the Montana Department of Agriculture, says this “integrated” approach is making inroads into existing infestations. Spotted knapweed has taken the biggest hit, declining from 4.5 million infested acres in 1985 to about 2.8 million acres today. Though that reduction has been partly offset by new infestations of other species, over the past decade Montana has reduced the amount of land with noxious weeds by 500,000 acres.

According to the 2008 Montana Noxious Weed Summit Advisory Council, private land managers, county weed districts, and federal and state agencies now spend a total of $21 million each year in Montana on noxious weed control. (The council calls for spending nearly three times that amount to slow the spread and reduce existing infestations by 5 percent each year.)

In addition to containing and eradicating weed infestations, a major goal of the weed war is to prevent new noxious plants from taking hold. Public education is critical. Burch says the more people who know about noxious weeds, the more likely early infestations can be detected and then treated before the plants take over. He tells of a retired Forest Service employee who reported a stand of yellow starthistle discovered while hiking near Dillon. The county weed district quickly treated the site. “That shows how important it is for people to be able to identify weeds and report them to us,” Burch says. “Yellow starthistle is not prevalent in the state, and we want to keep it that way.”

FWP is a key player in the state’s noxious weed management plan. Joe Weigand, the department’s statewide weed coordinator, says FWP is responsible for managing noxious weeds on 610 sites across the state comprising 410,000 acres. Working with state, federal, and county programs, the department spends roughly $650,000 each year for on-the-ground weed control and other management, in addition to several million dollars in grants and other payments that landowners and others may use to manage weeds (see sidebar at left). Along with educating the public and applying herbicides, FWP’s integrated management approach includes pulling weeds by hand, using cattle grazing to help native range resist weed invasions, and releasing beetles and other natural insect predators to attack the weeds. “We use every tool available,” says Weigand.

Thompson says being a good neighbor is a top priority for the department. “Wildlife management areas are part of a community, so we put a lot of emphasis on controlling weeds along the borders with our neighbors,” he says. “We understand that a landowner on one side of the fence can spend a ton of money on weed control and then see those efforts wasted if the neighbors aren’t doing their part too.” Weigand adds that FWP is required to control weeds on its lands, and that a law passed by the 2009 legislature mandates the department to develop a noxious weed management plan for any land it proposes to buy.

While nearby landowners support FWP weed control, other Montanans criticize the department for using herbicides. The chemicals can harm native wildlife forage and, when used at fishing access sites, contaminate streams and lakes. Weigand says the department is using more biocontrols to reduce the need for chemical applications. “We’re very cautious about how, when, and where we apply herbicides,” he says. “But broad herbicide applications are necessary where we have massive weed infestations, especially to save wildlife forage production. In the long run, we believe eradicating noxious weeds is best for the land and for wildlife, and using herbicides is usually the lesser of two potential evils.”

One thing’s for certain: Noxious weeds aren’t going away by themselves, whether on FWP lands or any others. The looming threats to agriculture and natural ecosystems mean that Montana can’t stand by and do nothing. To keep existing infestations from spreading and prevent new species from taking root, the state may have to be as pugnacious and persistent as the weeds themselves.Bear bullet

Dave Stalling is a past president of the Montana Wildlife Federation and a previous conservation editor at Bugle. He currently lives in Berkeley, California, where he is the communications director for Trout Unlimited of California.

FWP’s battlefront on FWP lands

At the new Marias Wildlife Management Area and State Park near Shelby, FWP has released root-boring weevils at 20 different sites to control noxious weeds. The department also spot-sprayed herbicides on roads, trails, and river corridors, and aerially sprayed 300 acres. “Keep in mind that the previous owner had done no weed control at all for the previous 50 years, so it will take us some time to get a handle on the weeds there,” says Graham Taylor, FWP regional wildlife manager in Great Falls.
The activities at Marias are just a snapshot of the noxious weed control FWP does at state parks, wildlife management areas (WMAs), and fishing access sites. In 2010, the department:

“I’m encouraged to see how our long-time managers pass their experience and knowledge about noxious weeds to the new managers,” says Joe Weigand, FWP noxious weed coordinator. “They’re committed to not lose any ground they’ve gained over the years.”

Join the Fight

The best way to battle noxious weeds is to prevent new infestations and stop the spread of existing ones. Here’s how:

For more information:
FWP Noxious Weed Management Program or e-mail:
Montana’s Statewide Noxious Weed Awareness and Education Program
Montana Department of Agriculture Noxious Weed Program or e-mail:
The threat of aquatic invasive species, including plants: