Resources: Winter 2000
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Invasive Weeds
Know No Borders Know No Borders

Like other Western states, New Mexico is home to wide open spaces-spaces that provide comfortable homes for invasive weeds such as Russian knapweed, Canada thistle, African rue and leafy spurge. As their names indicate, weeds have arrived from well outside New Mexico's borders.

"We are on a threshold," says Richard Lee, weed scientist with NMSU's Cooperative Extension Service. "The weed population appears to be increasing exponentially in certain areas of our state."

Diffuse knapweed

Pretty Problems

Invasive weeds that choke out native vegetation are creeping into the Four Corners area from the north, south, east and west. This "slow-motion explosion" was apparent earlier this year when diffuse knapweed was first recognized near Farmington.

Diffuse knapweed is unpalatable and poisonous to livestock and wildlife. The multistemmed annual stands 1 to 2 feet tall. When the flowers bloom from July to September, the plants are covered with white, rose or purple blossoms.

"This invasive plant literally owns southern Denver," Lee says. "How it moved from Colorado into New Mexico is anyone's guess." Diffuse knapweed can spread when dried seed heads attach to vehicles, people or animals.

Other knapweed varieties also are major problems in the Four Corners area. Russian knapweed is the most common, overtaking fields and empty lots like wildfire.

Spotted knapweed

"Russian knapweed spreads by black, deep-growing roots, which can penetrate to a depth of more than 8 feet," Lee says. "These roots emit toxic chemicals that inhibit growth of other plants around them."

Spotted knapweed is unpalatable to animals and displaces native vegetation, causing permanent changes to the ecosystem. The plants have large taproots. "This is a problem on hillsides where spotted knapweed has crowded out the native plants," Lee says. "The taproots aren't able to hold the soil and prevent erosion like the fibrous roots of native species."

Lee is concerned that spotted knapweed's purple flowers mask its problems.

Many invasive weeds around the state have beautiful flowers, making them attractive picks for home floral arrangements. "New weed infestations can occur when people transport the pretty flowers," he says.

Yellow toadflax

Yellow toadflax, sometimes called butter and eggs, was actually introduced as an ornamental plant. "It's a member of the snapdragon family that people liked because it was pretty. Now it has escaped and become an aggressive, competitive species."

The perennial plant sports numerous yellow flowers. Its extensive root system makes the plant difficult to control as it crowds out other plants.

"Leafy spurge is one of our more toxic plants that's spreading rapidly," Lee says.

The vigorous perennial infests almost 2.5 million acres in North America. Yellow, heart-shaped flower petals enclose seed capsules that explode when dry. "When these capsules explode, seeds can be projected up to 15 feet, making this weed extremely difficult to control." Plants along ditches and rivers can send their seeds downstream easily by ejecting them into the water.

Leafy spurge

Leafy spurge can burn the mouths of horses and cows. The plants contain a milky substance that, if rubbed on the face, can cause blindness or a rash around the mouth and eyes.

"All of these nonnative plants came into the country without their natural checks and balances," Lee says. "As a result, we're losing land in the West to weed infestation at a rate of more than 200 acres per hour, 5,000 acres per day. If we choose to ignore the problem, it will only get worse."

Sensible Solutions

New Mexico and Oklahoma are the only two Western states that have no laws requiring noxious weed management. Economic losses caused by the weeds have forced other states to implement such laws.

Lee is working with the New Mexico Department of Agriculture to establish a noxious weeds law here. "Fortunately, we're not alone," he says. New Mexico's three neighbors that help form the Four Corners-Arizona, Utah and Colorado-already have laws in place.

Telling the story: Helping people identify invasive weeds as potential problems instead of as pretty flowers is Richard Lee's goal.

"Weeds know no boundaries," says George Beck, Extension weed scientist at Colorado State University. "You've received some of your weed problems from us, like leafy spurge, which traveled down the Animas River from Colorado. And New Mexico, in return, has given us some of its weed problems."

Each state has certain common weeds. As these weeds spread into surrounding states, it's only natural for scientists to collaborate and share their knowledge.

"We've had leafy spurge, diffuse knapweed and Canada thistle that are just now being introduced into New Mexico," says Tom Whitson, Extension weed specialist with the University of Wyoming. "Let's each share information so we don't all have to reinvent the same wheel."

Beck and Whitson were among several scientists from neighboring states who helped with the Southwest Noxious Weed Short Course this summer in Farmington.

The annual short course draws participants from as far away as Idaho and California. Attendees include ranchers, U.S. Bureau of Land Management personnel, state highway department employees and others interested in managing invasive weeds.

"We've improved our chances of discovering weed infestations through this type of education," Lee says. "We're focusing on plants of concern. And we're telling people about them-how to identify them and how to manage them."

To help with identification, Lee recently published a pocket-sized guide to New Mexico's invasive weeds. Funded by several state and federal land management agencies, the spiral-bound booklet contains color photos, descriptions and known locations of 25 invasive weeds.

Yellow toadflax

The guides are being distributed through local county Extension offices. "Our goal is to help farmers, hikers and other New Mexicans identify the fast-spreading weeds so they can be contained," Lee says.

Once an infestation is found and identified, NMSU researchers are expanding their control to include mechanical, chemical and biological methods. "None of these is a stand-alone treatment," Lee says. "Only through integration of all management options will we see success."

One such success has been the introduction of Aphthona flea beetles. Already in use in Montana, Wyoming and the Dakotas, the flea beetle feeds primarily on leafy spurge. During the past seven years, NMSU researchers have released flea beetles in spurge-infested areas around the state.

"We also have to consider revegetation in our management plans," Lee says. "If weeds are removed from an area without arranging for revegetation, the weeds will return."

Controlling imported weed species with introduced insects and replacing them with noninvasive varieties is just the beginning.

"Awareness is critical across state lines if action is to take place." Lee says. "We've got to tell the story of noxious weeds and urge people to avoid spreading seeds."