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That lovely bamboo in your yard? It's not bamboo. And it's killing local plants.

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Japanese knotweed
The fat stalks of Japanese knotweed plants grow to almost an inch thick and sprout in dense thickets that crowd out other species of plants. It takes three to five years of herbicide application to kill the plant.
MPR Photo/Dan Kraker

"This stuff scares me."

Judy Gibbs points to a patch of Japanese knotweed along Keene Creek next to a busy street in West Duluth. The dense thicket towers more than 10 feet high. It's not supposed to be here. It's out of control, crowding out native plants and threatening to make its way from the Keene down to the St. Louis River.

"This stuff grows so fast," says Gibbs, who oversees trees and trails for the city of Duluth Parks and Recreation department. "That area is an important bird area for waterfowl, all kinds of migrants, so if this got along the St. Louis River, it would be devastating."

State officials are struggling to fight the spread of knotweed, buckthorn, wild parsnip and other noxious weeds. There's an "eradicate list" for species with the most serious potential economic, environmental or health impacts. But it's a battle fought on thousands of fronts against a clever enemy.

"You can't even see spruce trees, because this stuff just climbs up over them, and covers them, and eventually it breaks trees."

The knotweed, also known as Japanese bamboo, first came to the U.S. as an ornamental plant. It's now spread outside of backyards, mainly when plant fragments are washed down streams and rivers.

Map: Track the spread of Japanese knotweed

In southeast Minnesota, a woody vine called oriental bittersweet has spread quickly along the Mississippi River, said Anthony Cortilet, who coordinates the state's noxious weed program.

"There's some pretty serious infestations in Winona that are just amazing," he said. "You can't even see spruce trees, because this stuff just climbs up over them, and covers them, and eventually it breaks trees. It's pretty serious."

A recent $350,000 state grant from the state's Environment and Natural Resources Trust Fund will help combat oriental bittersweet, Dalmation toadflax, Cutleaf teasel, Japanese hops, and Grecian foxglove. Cortilet says that's important, because until now most funding has been geared toward enforcement and education.

"It's really the first time that we've been able to get some money for direct boots-on-the-ground type of management, and that's really needed here in Minnesota."

Meanwhile, the state Department of Natural Resources has launched a new public education campaign called "Play Clean Go."

The goal is to educate the public about invasive species that spread across the land, DNR terrestrial invasive species coordinator Laura Van Riper said. The approach is similar to the agency's "Stop Aquatic Hitchhikers!" campaign informing the public about zebra mussels and other invasives in lakes and rivers.

It's illegal to sell or transport plants on the "eradicate" list and landowners must try to get rid of them.

But preventing an invasive plant from taking root in Minnesota is much easier than trying to eradicate it once it's here, Van Riper said.

That's exactly what people in Duluth are discovering with Japanese knotweed.

Lowell Cobb first saw the flowering stalks in his yard as beautiful and encouraged them. Now, he said, the knotweed is "like a cancer. It's going to take over unless I do something about it."

He and other Duluth residents took part in a workshop last week to learn how to remove the stubborn plant from their property.

To help, Judy Gibbs with the city's Parks Division later handed out small containers of herbicide. "So you cut your stalk, you take the cap off and just go around the edge of the stalk," she said. "But you have to do it to every stem."

And, she cautioned, it could take three to five years of weekly applications to finally kill the plant.