Experts fear invasive species in Winona woods

Halloween is right around the corner, and there’s something lurking in a Winona forest that’s keeping biologists on high alert.

T hey call it the werewolf of the forest.

It’s not a ghost or a monster. It’s an invasive species of vines called Oriental bittersweet, a nd it’s killing trees at an alarming rate.

Bruce Eng, a retired Department of Natural Resources employee who now spends his days fighting Oriental bittersweet said, “It’s called the werewolf of the forest. It has the potential of taking the forest and just bringing it down.”

Eng said it has to be stopped.

“It’s a war. It’s critical. It’s important to go after it and stop the spread,” Eng said.

Like a python, the vines wrap around and strangle their prey.

“It goes around them very tightly and over and over and it girdles them so they can’t get their nutrients up under the bark and eventually it will suffocate them in that way,” Eng said.

Any tree can fall victim to the vines.

“It takes them down, even the big oaks,” Eng said.

Anne Morse, the sustainability coordinator for Winona County, said, “I don’t know of any place that has a worse problem than we do.”

Morse said Winona County has the worst Oriental bittersweet problem in the state.

“There isn’t anything that keeps it in check,” Morse said.

She’s leading volunteers and students at St. Mary’s University in Winona to clear the woods behind the school.

“We do our best to cut as many of these as we can, so then we can treat with the herbicide,” Morse said.

Even though experts think the vines have been in Winona for more than 50 years, the county just recently discovered them.

“Until five years ago, we at the county didn’t even know we had this infestation,” Morse said.

That’s partly what makes Oriental bittersweet so dangerous.

“It’s insidious and it’s sneaky. You don’t think you have it, and all of a sudden, you just kind of notice it all over your trees,” Eng said.

Despite the group’s hard work, the vines are still spreading.

“It’s just a matter of time. It’ll be down in La Crosse,” Eng said.

If you think you have Oriental bittersweet, make sure you cut the vine near the root and spray it with herbicide.

If you don’t spray it, the vines will only come back stronger.

If you would like to volunteer to help get rid Oriental bittersweet in Winona, you can go to

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