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Leafy spurge—a tenacious, destructive weed—is controlled by teams at Teddy Roosevelt National Park through the use of BASF's Plateau herbicide. Photo: BASF

Thousands visit Teddy Roosevelt National Park in Medora, N.D., each season, but few notice one of the park's greatest threats—leafy spurge.

“Leafy spurge can survive almost anywhere,” said Chad Prosser, liaison for the Northern Great Plains Exotic Plant Management Team, responsible for ridding 14 national parks of noxious and invasive weeds. “If we didn't do anything, it would occupy 100% of the park—it grows in sun, shade, dry soil, or moist soil.” It displaces native vegetation and forms a monoculture that can reduce grass production by 75%.

Terry Cacek, exotic weed specialist for the National Park Service, notes that bison, elk, wild horses, and deer won't eat leafy spurge because its sap is irritating and can cause ulcers in their mouths. “If we let this plant take over, we would have no grass- and shrub-eating animals left in this park.”

Leafy spurge spreads in numerous ways. “Horses can get the seeds in their hooves,” said Prosser. “Cars and mountain bikes can get them in their tires and hikers in the soles of their shoes.” Campsites and recreational trails are some of his greatest concerns.

Treating leafy spurge requires a well-planned, integrated pest management (IPM) solution. Prosser's IPM plan includes biological and chemical control, prescribed fire, and reseeding with native grasses and forbs. Leafy spurge has a deep root system, is difficult to control, and its seeds can lie dormant in the ground and produce seedlings as long as eight years after deposit. When seed pods burst, the seeds can fly up to 15 feet.

Flea beetles have proved a good biological tool for controlling leafy spurge in the park's remote areas. Adults eat the leaves, larvae feed on the root system, and they are harmless to other plants and animals. Last year, Prosser's team released more than 8 million flea beetles at 790 sites throughout the park.

Prosser's IPM plan also includes Plateau herbicide, from Ludwigshafen, Germany-based BASF; the chemical effectively controls leafy spurge while releasing desirable grasses, forbs, wildflowers, and legumes. The fall-applied solution penetrates deep into the roots when the plant is storing nutrients for the winter. In the spring, when the weed emerges from dormancy, the herbicide inhibits the plant's ability to produce new foliage by slowly exhausting food reserves. The structure eventually dies.

Prosser determined 1050 infested acres needed to be sprayed by foot, an all-terrain vehicle (ATV), or helicopter. His team applied 8 ounces per acre, two weeks following Labor Day when the park was relatively empty and the chemical would work most effectively. He relied on the all-volunteer Montana Conservation Corps to do most of the backpack spraying and park employees to run the ATVs.

Efforts have paid off. “The combination of flea beetles and Plateau produces excellent results,” said Prosser. Every year he returns to a treated area, he finds a reduced leafy spurge density, and the next treatment involves less herbicide and shorter application time. Seeing other grasses flourish where leafy spurge once dominated, Prosser knows he's found a long-term solution. Cacek calls Teddy Roosevelt a “flagship park for invasive weed control.” According to Prosser, “We have to be vigilant so that we can keep this park as natural as possible.” PW

Andrea Cuff is a Minneapolis-based business writer.