NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

July 1, 1999

NDSU Researcher: Leafy Spurge Control Making Progress

North Dakota has more acres infested with leafy spurge today than it did 20 years ago, but in 1979 the state's leafy spurge acreage was doubling every 10 years, says a weed scientist at North Dakota State University. Since 1991, there has been virtually no increase in leafy spurge acres, and in fact, 16 of North Dakota's 53 counties now report having fewer leafy spurge acres than in 1979.

"We've stopped the doubling. That's the big thing," says Rodney Lym, a professor in the Department of Plant Sciences at NDSU. Lym specializes in invasive weed control research.

Efforts to control leafy spurge represent the most aggressive battle ever waged against a weed in the northern Great Plains, says Russell Lorenz, a weed scientist, now retired, with USDA's Agricultural Research Service in Fargo. In 1979, more than 125 scientists, state legislators, land managers, farmers and ranchers met in Bismarck for the first Leafy Spurge Symposium. The symposium has become an annual event.

"Spurge has brought a lot of government entities together with private interests to take on the problem," Lym says.

After the first symposium, H. Roald Lund, then director of the North Dakota Agricultural Experiment Station, formed a leafy spurge team at NDSU that included a weed scientist, an entomologist, a plant pathologist and a botanist. Lym says the thinking in 1979 was that a pathogen would be the first biocontrol agent available to fight leafy spurge. Unfortunately, researchers have identified several pathogens for leafy spurge, some quite virulent, but other crops such as alfalfa are also susceptible to the diseases these pathogens cause.

While attempts to infect leafy spurge with diseases has not yet produced results, another element of biocontrol has: insects. Lym says 11 insect species have been introduced into North Dakota. He adds, "By far, the flea beetles have been the most effective to date."

During the past two decades, researchers have also been able to identify a number of grass species that are competitive with leafy spurge. These species include Bozoisky Russian wildrye, which multiyear trials in North Dakota show provides 40-percent control; Manska pubescent wheatgrass (70-percent control); Rebound smooth brome grass (80 percent); Rodan western wheatgrass (70 percent); and Arthur Dahurian wildrye (60 percent).

Research has confirmed that grazing sheep and Angora goats on leafy spurge-infested pasture and rangeland provides an effective alternative to using herbicides in some situations, although grazing alone will not eradicate leafy spurge, Lym says. Instead, grazing will reduce the density of leafy spurge infestations. The decision of whether to use sheep or goats for grazing is dependent upon the livestock facilities available (fencing, buildings etc.) and prevailing market prices for the animals.

"Today we have many more cost-effective herbicides that are doing a good job of controlling leafy spurge," Lym continues.

Besides the standards for leafy spurge control—2,4-D and Tordon—herbicides now labeled for use in North Dakota include several products containing the active ingredient glyphosate (Roundup Ultra/RT, Touchdown and Rodeo, for example). One newer product, Landmaster BW, is a combination of glyphosate and 2,4-D, and there are a number of herbicides with other active ingredients, such as Krenite, which contains fosamine as its active ingredient, as well as Casoron 4G (dichlobenil) and Plateau (imazapic). In addition, Paramount was recently labeled for leafy spurge control in North Dakota along roadsides, fence lines, rights-of-way and noncrop areas, Lym says.

Research with quinclorac, the active ingredient in Paramount, has been under way at NDSU since 1993. This research has shown that the best long-term control of leafy spurge resulted from applications of Paramount in combination with a methylated seed oil (MSO). Twelve months after application at a rate of 1.5 pounds of Paramount per acre, the herbicide-MSO combination averaged 77 percent control, Lym says. But as currently labeled for North Dakota, the maximum allowable rate for Paramount applications is only 0.4 lb/A.

"Even at the current labeled use rate, Paramount will provide good leafy spurge control with minimal injury to desirable species," Lym concludes. "It is likely that once Paramount receives a full registration, the use rate will be increased."

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Source: Rodney Lym (701) 231-8996

Editor: Dean Hulse (701) 231-6136