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Spotted Knapweed Invading County

August 2, 2012

Spotted Knapweed flowers are pinkish-purple and visible during July and August.

An invasive plant species is keeping area ranchers and the Barnes County Weed Control Board on its toes.

Weed Control Director Jim McAllister said Spotted Knapweed has been in the area for about eight years, but now it is threatening a widespread infestation.

“We consider there’s probably 225 acres infested, and the bad part about it is it makes pasture virtually worthless,” he said. “The Knapweed is an annual or a short-lived biennial, but it still has the ability to choke out anything that’s growing.”

McAllister said the infestation can partially be traced back to a Montana grass seed company that sold grass seed to local farmers that were converting crop land to pasture land. Each plant produces about 1,000 seeds that are viable for up to 7 years, and are transported by vehicles, railroads and rivers. Commonly found along the medians of Interstate 94, McAllister said he recently found a plant near the Valley City National Fish Hatchery on County Highway 19.

“To find it out here is odd, but then again, maybe it isn’t. A lot of people travel this road on their way to the lake,” he said.

The plant grows to be 2 to 4 feet tall with several flower stems that grow from the roots. It is easy to spot in July and August due to its pinkish-purple flowers. It gets its name from the black-tipped flower bracts from which the flower blooms. It can also release toxins into the soil to keep other vegetation from growing.

McAllister said the best offense against invasive species is prevention, which is also the most cost-effective. Herbacides Picloram, Dicamba and Clopyralid + 2,4-D are effective in fighting the weed but an area must be monitored for several years and possibly retreated due to the seeds long validity. If land owners choose to spray an area themselves, McAllister asks that the Weed Control Board is notified.

“We would prefer to know about it so that we can mark it and watch it.”

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