How to Identify and Control Oriental Bittersweet (Celastrus orbiculatus)
Invasive Species Spotlight: Oriental Bittersweet (Celastrus orbiculatus)
Readers’ Note: Know Your Land is an informational series intended to educate deedholders on potential invasive species in their field or woodlot. We provide descriptive information, interesting facts, and strategies for managing these species.
Ask a biologist or forester what would make their top 5 list of ‘the worst’ invasive plants and you would almost certainly get a different response every time. But working in the forests of southern New England, Oriental Bittersweet (Celastrus orbiculatus) makes our list without hesitation. Introduced as an ornamental between 1860 and 1879 in New York, bittersweet has spread to at least 25 US states.
Description
If you’ve ever driven along Massachusetts’ tree-lined roads in early autumn and noticed pale green or yellow leaves still clinging to the trees after the maples have dropped theirs—or hiked the edge of a winter field and spotted yellow and red berries twisting up a trunk and through the canopy—you’ve likely seen bittersweet. And once you’ve noticed it, it’ll show up everywhere you look.
This fast-growing deciduous woody vine will start out as thin as a pencil and in a few short years will be as thick as your wrist, wrapping itself around a tree and girdling it, starving it of nutrients and water, and ultimately killing it.
Oriental Bittersweet leaves are in an alternate arrangement and leaf shape varies from elliptic to obovate (looking for help with leaf shape?). Fruits are red in color, spherical-shaped, and have a green, becoming yellow (in autumn) casing that is highly visible. If you are still looking for confirmation, look at their unmistakable orange roots.
Strategies for control
Oriental Bittersweet possesses several strategies that give it an advantage over our native plants:
- It grows fast — from 1-12 feet a year and can reach up to 60 feet in height.
- It grows well in sun or shade (while most visible along wooded edges, it is not uncommon to find it growing in the interior forest understory).
- Bittersweet can spread via seeds or through root suckering, and
- One of its primary methods of seed dispersal is birds, who consume the fruits that persist through winter.
Controlling bittersweet can be very challenging. To save the host tree, vines can be cut and will eventually rot and fall off the tree. However, hand pulling the remaining vine shoot and/or repeated cutting of resprouts is necessary to eventually exhaust the plant’s resources and kill it. Alternatively, what is generally considered the most effective approach is a combination of mechanical and chemical control.
Cutting the vine and ‘painting’ the cut surface with a systemic herbicide such as glyphosate or triclopyr (often referred to as cut stump treatments) ensures the root system is killed with the minimum amount of chemical. Foliar spraying of the leaves is typically not recommended unless you are trying to control young shoots that are not yet wrapped around a tree. Cut stump treatments may be conducted year-round. Follow-up monitoring and maintenance is important both to address root suckering and resprouting but also to treat new plants because bittersweet seeds can remain viable in the soil for two years or longer. For more information on controlling bittersweet visit here. If you choose to use herbicides, be sure to read and follow instructions provided on the label and follow all applicable regulations from the Massachusetts Department of Agricultural Resources.
What about our native bittersweet?
Massachusetts does have a native species of bittersweet, American bittersweet (Celastrus scandens). At a quick glance it may appear similar to our invasive bittersweet, but the leaves are narrower and more elliptical and the fruit/flower arrangements differ. American bittersweet is a state-threatened species that has declined due to habitat loss and possible competitive displacement caused by Oriental bittersweet. A recent study suggested that Oriental bittersweet ‘hybridizes asymmetrically’ with American bittersweet, effectively reducing the native plants presence in the environment.
The problem with bittersweet wreaths
Bittersweet vines have a long tradition of being used in holiday wreaths. While they are undeniably gorgeous, you run the risk of spreading the invasive to other areas. Therefore, it is best to avoid using bittersweet in a wreath. Properly disposing of the bittersweet wreath is very important. You should either burn the wreath (be sure to follow local ordinances) or put it in a black plastic bag and solarize it for a minimum of a month.
Need more help?
If you have a forest management plan or stewardship plan on your property and have invasive plant issues, talk with your forester about it. They can direct you to resources and contractors that can assist you. If you don’t have a plan, consider reaching out to your local USDA NRCS office. Their staff can walk your land with you and provide free technical assistance.