The Carlisle Mosquito Online

Friday, September 24, 2010


Invasive Orange: Oriental Bittersweet

There is nothing sweet about these berries.(Photo by Drew Kissinger)

See the orange roots (Photo by Drew Kissinger)

A dead maple tree engulfed by Oriental Bittersweet. (Photo by Marjorie Johnson)

Earlier this month we learned about Glossy Buckthorn with black fruit, black roots and orange wood in the center of the stem. This week we have another orange enemy of our woods: Oriental Bittersweet. Planted in gardens for its beautiful bright orange seeds framed by a charming four-petaled cover that opens in late fall, this native of Asia has escaped the garden and is literally consuming our woods.

This week is the perfect time to go out and learn to identify this aggressive and pervasively invasive vine in Carlisle, because right now it is covered in yellow-green, ripening berries. When you go to the transfer station this week, keep driving down Elizabeth Ridge Road and then follow Sunset Road until it ends in the cul-de-sac. In the circle of grass in the center of the cul-de-sac is a perfect specimen of this destructive beauty in full glory. What you are looking at is what used to be a tall tree – perhaps a maple? It’s hard to tell because it has been completely consumed and killed by Oriental Bittersweet!

The destructive power of this vine is stunning. The vines and foliage weigh down, shade out and collapse the tree from above, while the roots choke off water and food from below.

Get out of your car and take a good close look at the leaves, the color and texture of the vines, and especially the fruit. The thick vines are coiled around the tree. The leaves are oval shaped with a jagged edge. The leaf veins branch to the edge from a central vein. Crush the bitter berries, feel the shell break away, and see the white maturing seeds inside the bright orange flesh. This fall, the shell will open up and reveal the ripe bright orange berries. Underground, the bright orange roots form a thick network that spreads far from the vines. New shoots will pop out of the ground all along the network.

Now turn from the spectacle of a tree that’s been slowly murdered and walk 30 feet up the Old Morse Road Trail which continues here at ten o’clock (if the road enters the cul-de-sac at six o’clock). This one-acre parcel is being consumed by Oriental Bittersweet. All of the vegetation is being replaced by aggressive tendrils no doubt springing from the mature network of bright orange roots underlying the whole area. The tendrils are climbing every vertical surface; fences, trees, stone walls, even the stalks of wild raspberry. The vine is creating its own sunny woodland border habitat by consuming the forest from the outside in.

Now that you can identify it, keep an eye out for it. you’ll start to see it in many places in Carlisle. It likes to start at the edge of the woods and work its way in as it kills the border. A great example of this is across Curve Street from the Bog House where the trees along the road are being consumed. You’ll see it killing trees along the farm fields in the park, and killing many of the trees around the DPW shed at the transfer station.

There is a native species of bittersweet that is easy to distinguish due to its rarity (I have never seen one in Carlisle) and the fact that its berries grow only at the ends of the vines as opposed to Oriental Bittersweet which bears its fruit anywhere along the length of the vine.

To remove Oriental bittersweet, start by cutting the vines to destroy the top growth. It is very difficult to remove by hand and involves lots of digging to trace and remove the roots. The vine will re-sprout profusely from any large roots that remain in the ground. The Minnesota Department of Natural Resources has a good website that describes each invasive species and mechanical and chemical means to control it. ( Keep in mind that by removing invasive species we are trying to conserve nature in our beautiful town (our water supply included), so be circumspect and careful when using chemicals. Before you do anything near wetlands be sure to get approval from the Conservation Commission.

The vine will also start from seedlings each spring for several years until all the viable seeds in the soil are spent. These little seedlings have a small root structure and will die when pulled out of the ground and hung to dry – don’t lay them back on the ground. The seedlings tend to look a bit different than the more established plant, and it is a good idea to learn to recognize it at this stage, because the seedlings are the only easy stage of this plant to kill.

Oriental Bittersweet is a tough customer and removing it from an area takes some hard work and persistence, but it is worth the effort. It is arguably the most destructive invasive species in town.

Submissions and ideas for the Biodiversity Corner are encouraged on any species that occurs in the wild and was seen in Carlisle. Send a note, a photo, or the whole column to If you have a mystery species, send that too. ∆

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