NEWS for North Dakotans
Agriculture Communication, North Dakota
State University
7 Morrill Hall, Fargo, ND 58105-5665
June 4, 1998
Vigilance and prompt control measures are a key to keeping several weed species at bay in North Dakota, notes a North Dakota State University weed expert.
There are several emerging weed threats in North Dakota, according to weed scientist Rod Lym. Lythrum, commonly called purple loosestrife, is beginning to invade the state's wetlands and waterways, and several species of knapweed are invading range and crop land.
"If we've learned anything from the weeds that are already big problems in the state, it's that it's much more effective to get after problems early," he says. "Once we start talking about thousands of acres of infestation, the control becomes much more costly and complex."
Purple loosestrife, a beautiful garden plant with an aggressive nature, has been in North Dakota for at least 50 years as a cultivated flower. It's been shown that these garden varieties of purple loosestrife, once thought to be sterile, can cross breed with wild varieties. In the wild, purple loosestrife crowds out native plants and destroys habitat for ducks, muskrats and other wildlife. Heavy infestations can reduce stream flow.
Even with infestations in or near Grand Forks, Fargo, Valley City and Minot, there is less than 50 acres of purple loosestrife in the entire state. "That makes it a very manageable infestation," Lym says.
In 1996, purple loosestrife was placed on the North Dakota noxious weed list which includes the weeds considered by North Dakota officials to pose the most serious economic or health threat. Purple loosestrife is the only weed on the list that does not pose a threat to the state's crops or rangeland.
"The environmental threat posed by the plant was enough for it to be added to the list," Lym explains. Purple loosestrife clogs thousands of acres of wetlands, lakes and waterways in Minnesota and other nearby states and provinces. It can spread when seeds float away and sprout or broken parts of the plant take root.
"If you see an infestation, contact your county weed officer," Lym says. "With such a small infestation, we have a very good chance of keeping this weed contained."
Because purple loosestrife doesn't yet cause an economic loss, Lym and other researchers are looking for insects and other biological methods of controlling it. The most identifiable characteristic of purple loosestrife is the striking rose- to purple-colored flowers arranged on a spike that can be from a few inches to three feet long. It typically flowers from early July until first frost in North Dakota.
Meanwhile, three species of knapweed, relatives of the thistle, are also threatening the state.
"These weeds are currently the No. 1 threat to agricultural acreage in North Dakota," Lym says. "These weeds spread faster than thistles and have the potential to eclipse leafy spurge in acreage and rate of spread."
Leafy spurge is the current king of weeds in North Dakota rangeland, spreading rapidly and stubbornly resisting attempts to kill it. Current knapweed infestations in North Dakota are found primarily along highways, waterways, railroad tracks, pipelines and recently constructed utility lines. It spreads by seed in hay, on vehicles or in contaminated seed. The three species are:
n Russian knapweed. This species has been in North Dakota for many years and infests about 3,500 acres. It's a perennial with black, spreading roots that form new shoots. Its growth characteristics are similar to those of Canada thistle. It's the only one of the three species that causes significant crop losses. It can be identified by the rounded bracts with transparent tips at the base of pink to lavender flowers. Largest infestations are in southwestern North Dakota. The plant is adapted to poorly drained and saline and alkaline soils
n Spotted knapweed. This species is a short-lived perennial or biennial with a taproot. It can be most easily identified by the black tipped bracts located at the base of the pink- or cream-colored flowers. Typically a problem in rangeland, the weed is also making inroads on no-till and minimum-till crop acres. The plant infests about 1,500 acres in North Dakota. Infestations may remain in a confined location for several years then spread rapidly. It's important to control the weed as soon as it's identified and monitor the location for regrowth.
n Diffuse knapweed. This is also a short-lived perennial or biennial with a taproot. Its bracts are spiny or crab-like at the base of white- to rose-colored, or sometimes purple, flowers. Diffuse knapweed is difficult to distinguish from spotted knapweed without looking at the bracts. This species infests only 20 acres in North Dakota, but has the potential to spread significantly.
"There's a lot of potential for spread with the knapweeds," Lym notes. In Montana and Minnesota, knapweeds infect more acres than leafy spurge. At least one of the three species has been found in 25 counties in North Dakota.
"People are the major cause of knapweed spread," Lym notes. "Producers should exercise caution when using hay from road ditches or purchasing hay from infested areas. And land managers need to learn how to identify and control these plants. Timely control now will be very cost effective compared to treating larger acreage later."
For more information on the knapweeds or purple loosestrife, contact your local office of the NDSU Extension Service. Ask for publication W-1146, "Know Your Knapweeds," or W-1132, "Identification and Control of Purple Loosestrife."
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Source: Rod Lym (701) 231-8996
Editor: Tom Jirik (701) 231-9629
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