Oriental Bittersweet Causing Woodlot Headaches
Posted: 02/22/2011

By itself, the small vine seems of little threat; maybe an ornamental wreath, with yellow capsules giving way to red berries...or perhaps climbing a trellis, with soft, green leaves.

But Oriental bittersweet doesn't travel by itself. And it doesn't stay small for long. The invasive transplant from eastern Asia is jumping the fence from backyards to woodlots. It's choking, shading and crowding out native trees, shrubs and other desirable plants in regions across the eastern U.S...and now in Iowa.

Marilyn Keller first noticed it three winters ago on her 29 acres near Cedar Rapids. "I would always see grape vines; Virginia creeper. This was a different vine, though," recalls Keller. "It was wrapping around a tree. It didn't come off easily. The little nodes had flowers; many times more than (American) bittersweet. By Spring, I could see it almost everywhere."

The vines grow low, across the understory of a wooded area. They grow high, into the top reaches of hardwood trees. Then they grow back down; to the ground. "You fight it low, where you can see it. You don't always look 80 feet up, to see it (going) from tree to tree; growing out to the sides and down again," emphasized Keller. She has been battling the fast growing vine ever since.

"It is a regional problem now," assesses Mark Vitosh, district forester for the Department of Natural Resources in the Cedar Rapids-Iowa City region. "However, it has a huge potential for exploding on you, if you are not in the woods a lot. In just a couple years, it can overtake an area."

Vitosh says not many woodland owners know what to look for. It looks similar to native American bittersweet. Look closely, though, and the imposter can be unmasked. Oriental bittersweet has rounded glossy leaves, alternately growing along the stem. Clusters of small greenish flowers-and eventually fruits-grow all along the stem. The American species has longer, narrow leaves, with fruits clustered at the end of stems. Just the sheer number of seeds produced gives the Oriental bittersweet a big advantage.

And once the invader takes root, it takes woodlot war to beat it back. Riding a couple months after first noticing the new vine, Keller realized her horse could not get through the thick, two-foot high mass of tangled vines. That is when she took the offensive.

Hiring two workers, they plowed forward. Hacking away at the thick vines ("Machetes work", says Keller), they would literally shove the tangled mass before them with the bucket of an endloader. Some of the vines had circled the trunks of trees, squeezing them, and shutting off nutrients through the cambrium layer. The workers piled vines-some five inches across-into piles to dry and then burned them. But not before the invader caused noticeable damage. "I lost two to three dozen large trees there," she noted, pointing to a ridge top along her property."

And control is not a one shot dose. Keller and her helpers comb the property; pulling small vines and trying to get to the problem before seeds drop. A broadleaf weed spray-one with triclopyer-helps. With the invader on neighboring property, she knows, though, it is just a fence line away from re-establishing itself.

"The key is to catch it early," urges Vitosh. "Otherwise, it is unbelievably hard to control." Vitosh warns that with its potential for mass seed production and its ability to overtake a woodland area and shade or choke out native plants, it as more destructive than garlic mustard.

He urges woodlot owners to watch for the invasive species; do a lot of vine pulling, especially when they are young and more easily removed. As it grows, cutting and herbicide application; a much more aggressive regime is needed, to control the fast growing shallow, wide root system.

"That is why it is so worrisome," admits Vitosh. "It grows on anything."