Invasive Species: Oriental Bittersweet

By Matt Forster

The classic image of the South, ancient trees dripping with Spanish moss, has changed in the past few decades. The trees are certainly draped with something. It’s the frightfully fast growing kudzu, which has spread from Texas to Virginia, Florida to southern Ohio, blanketing the South in a suffocating green quilt. The climate zones are gradually shifting northwards here in the United States, but so far our cold Midwest winters have kept the kudzu at bay.

Another Asian transplant, however, handles our winters just fine and has a secure foothold in the woods of Southeast Michigan. It is oriental bittersweet (Celastrus orbiculatus), and if you enjoy hiking in the area, you have seen this invasive species.

Oriental bittersweet is a woody vine that grows on the edges of forests and woodlots —eventually expanding those “edges” and creating an environment for itself: whole fields of creeping vines. It climbs trunks, stealing sunlight from the tree’s leaves. Eventually, the tree is weakened to where it can no longer support the weight of the vines. This often comes to a breaking point in the winter when the bittersweet increases the amount of snow and ice that collects on weakened branches and the trees topple.

It shouldn’t be confused with Michigan’s other vines: poison ivy (three leaves), Virginia creeper (five leaves), wild grape (grape leaves), and American bittersweet (Celastrus scandens).

As a cultivar—raised and sold by nurseries—the oriental bittersweet was a popular plant with gardeners for generations. It was brought from Asia in the late 1800s as an ornamental for domestic gardens. It was originally considered a hearty alternative to our native American bittersweet. The imported variety is ignored by deer and other pests, and the berries it bears in the fall are more impressive than those of the local bittersweet. Even now, people use the oriental bittersweet to weave decorative wreaths. (Of course, passing out wreaths of bittersweet is one of the ways in which bittersweet is spread.)

Unchecked, patches of oriental bittersweet have taken down acres of forest. Area park managers know too well the damage it can cause and can typically point you to a few devastating examples.

Woody vines, in general, are notoriously difficult to control. When they have been transplanted to an environment without any natural enemies, they become even more so. Poison ivy, for example, is a hassle to rein in, but at least the deer that find a field of poison ivy see an all-you-can-eat salad bar. No such luck with oriental bittersweet. The usual chemical controls (like Round-Up) don’t work. Mechanical controls (like cutting and mowing) simply stimulate further growth, vines sprouting up by the dozen with each vine trimmed.

When oriental bittersweet shows up in a park, the usual response is a round of controlled burns. Or volunteers are sent out into the woods with loppers and an herbicide that is applied directly to the cut stump. (This pulls the poison into the root directly.)

Of course, oriental bittersweet looks a lot like American bittersweet, and there is even rumor of them cross-pollinating. So you need to educate yourself on the subtle differences before heading out into the woods to hack away at the problem.

If you have oriental bittersweet on your property, there are a handful of resources to help you take control. First is the informative handout on oriental bittersweet published by the Michigan DNR. The Oakland Phragmites & Invasive Species Task Force (OPIS) also has a few resources for you.

In order to gather information on the spread of invasive species, the Midwest Invasive Species Information Network (MISIN) recently released an app. The program is free and there’s no cost to setting up an account. Once the app on your phone or other smart device, you can help local and regional experts track and eradicate invasive species.