Garden valerian is an invasive plant that's tall, tough and pungent. It's poisonous to cattle and has been muscling its way into northern Wisconsin ditches and fields since 2001. The town of Amnicon appears to be ground zero for the invader.

"The largest concentration of this valerian weed is right here in the town of Amnicon, that I can see," said Jerry Kroll, who winters 135 head of red angus at Kingbird Ranch.

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It's been spreading.

"And now it's totally out of control," Kroll said.

Driving along 22nd Road last week, fields to either side were thick with the white, lacy flowers of garden valerian, which tower above neighboring plants at 6 feet.

"This valerian, it basically kills off most of the vegetation, canopies it and chokes them out," Kroll said." New vegetation won't come in because that weed is there. It's definitely hardy stuff."

Garden valerian is spread through root nodes as well as seeds, according to Jane Anklam, horticulture and agriculture educator with the University of Wisconsin-Extension. Kroll said he doesn't see much in his fields, which are cut and grazed regularly. But with the current soft hay market, many landowners are choosing to leave fields uncut.

"Because these fields aren't getting cut, it doesn't take long and they're taking over," Kroll said of the invasive plant.

Garden valerian is an Asian plant that was brought to Europe and then the United States for medicinal and garden use, but it escaped.

It's invaded New England and a swatch of the Midwest, as well as a few patches in the far northwest, according to the United States Department of Agriculture. How it got loose in Douglas County is unknown. Valerian seeds may have been hidden in hay bales from outside the area. Plants may have escaped a local garden. Maybe seeds made their way here on Great Lakes ships.

However it got here, it's become a problem.

"I know it's impacting my farmers," Anklam said. "Most of them, they can't shrug it off anymore."

It's an economic threat, lowering the quality of hayfields and pasture land. It can also change local water quality, plant diversity and native habitats.

Even members of the public have started talking to her about "that stinky stuff," Anklam said.

Although invasive valerian reports date back to 2001, the number of sightings jumped from about 50 in 2007 to more than 250 in 2008. Today, 363 populations are currently known to exist within the state, most in northern Wisconsin, according to Mark Renz, assistant professor and extension weed specialist with the University of Wisconsin Madison.

Anklam said the invasive plant prefers cool, wet areas; open areas take off faster than wooded. She's noticed it spreading along road and trail corridors in the area, heading south.

Cattle won't eat it. Kroll let some of his herd graze through the ditches beside the road this spring. The only thing they left untouched was the valerian. But, Renz said, if it is dried and baled in with hay, livestock might not be able to tell it apart from the good vegetation.

Kroll's concerned about what will happen when the hay market heats up.

"And all this dormant seed that's laying there on top the ground is going to get raked up and baled and hauled off," he said. "And when those bales get hauled off, they're going to affect other fields elsewhere."

There's no management prescription yet for the invader. Douglas County's ground zero, however, may provide the key.

Renz and Anklam are testing eight different herbicides on a field of valerian in the town of Amnicon. Data compiled from the site will be used to provide recommendations for the rest of the state.

"I would love to get it nailed here, because it's being spread to the rest of the state and it's recognizable by the public," Anklam said.

She encouraged the public to call 715-395-1515 to report large plots of valerian in the area.

"It's not going to be if, it's going to be when," Anklam said.