(Celastrus orbiculatus)
Family: Staff-tree family (Celastraceae)
Native Range: China, East Asia, Japan, Korea
Oriental bittersweet is a deciduous woody perennial plant which grows as a climbing vine and a trailing shrub. Mature plants can attain stem widths of 4 inches in diameter and grow as high as 60 feet into trees. The leaves are alternate, glossy, nearly as wide as they are long (round), with finely toothed margins. There are separate female (fruiting) and male (non-fruiting) plants. Female plants produce clusters of small greenish flowers in axillary clusters (from most leaf axils), and each plant can produce large numbers of fruits and seeds. The fruits are three-valved, yellow, globular capsules that at maturity split open to reveal three red-orange, fleshy arils with each containing one or two seeds. Because of the abundance of showy fruits, oriental bittersweet has been extremely popular for use in floral arrangements.
Look-alikes
Oriental bittersweet can easily be confused with our native American bittersweet (Celastrus scandens), which is becoming scarce in the wild. Make sure that you have identified the plant correctly before starting control. American bittersweet produces flowers (and fruits) in single terminal panicles at the tips of the stems; flower panicles and fruit clusters are about as long as the leaves; the leaves are nearly twice as long as wide and are tapered at each end. Oriental bittersweet produces flowers in small axillary clusters that are shorter than the subtending leaves and the leaves are very rounded. Comparing the two, American bittersweet has fewer, larger clusters of fruits whereas Oriental bittersweet is a prolific fruiter with lots and lots of fruit clusters emerging at many points along the stem. Unfortunately, hybrids of the two occur which can make identification more difficult.
Ecological Threat
Oriental bittersweet is a vigorously growing vine that climbs over and smothers vegetation which may die from excessive shading or breakage. When bittersweet climbs high up on trees the increased weight can lead to uprooting and blow-over during high winds and heavy snowfalls. In addition, Oriental bittersweet is displacing our native American bittersweet through competition and hybridization.
Distribution and Background
Oriental bittersweet was first introduced into the U.S. in the 1860s as an ornamental plant. The species is often associated with old homesites from which it has escaped into surrounding natural areas. Oriental bittersweet is still widely planted and maintained as an ornamental vine, further promoting its spread.
Oriental bittersweet currently occurs in a number of states from New York to North Carolina, and westward to Illinois. It has been reported to be invasive in natural areas in 21 states (CT, DE, IL, IN, KY, MA, MD, ME, MI, MO, NC, NH, NJ, NY, PA, RI, TN, VA, VT, WI, and WV) and at least 14 national parks in the eastern U.S.
Oriental bittersweet infests forest edges, woodlands, fields, hedgerows, coastal areas and salt marsh edges, particularly those suffering some form of land disturbance. While often found in more open, sunny sites, its tolerance for shade allows oriental bittersweet to invade forested areas and persist for a long time in shaded conditions.
Biology and Spread
Oriental bittersweet reproduces prolifically by seed which is readily dispersed to new areas by many species of birds such as mockingbirds, blue jays and European starlings. The seeds germinate in late spring. Extensive seed reserves can become established in the soil within a year or two. Seeds of Oriental bittersweet remain viable for several years and control actions must continue until seed sources are eliminated. The species also expands vegetatively through root suckering.
Alternative Plants (Alternate Native Species)
Many attractive native vines are available that provide nectar, seed and host plant material for butterflies, hummingbirds, and other wildlife. Some examples for the eastern United States include:
- Virgin’s bower (Clematis virginiana)
- Trumpet honeysuckle (Lonicera sempervirens)
Whenever possible, use as alternatives plant species that are native and adapted to the ecological region where you live. They will be more valuable to the wildlife species that have evolved with them and depend upon them for food and shelter. Check with your local native plant society for recommendations and sources of native plants.
Management Options
A combination of cutting followed by application of concentrated systemic herbicide to rooted, living cut surfaces is an effective approach for removing Oriental bittersweet. For large infestations spanning extensive areas of ground, a foliar herbicide is recommended over manual or mechanical methods, which would create soil disturbance, to minimize soil disturbance.
For disposal options, refer to the control methods and disposal options page.
Plant Control
Manual, mechanical and chemical control methods are effective in removing and killing Oriental bittersweet. A combination of methods often yields the best results and may reduce potential impacts to native plants, animals and people. The method selected depends on the extent and type of infestation, the amount of native vegetation on the site, and the time, labor and available resources.
Biological Control
No biological controls are currently available for this plant.
Manual Control
Small infestations can be hand-pulled but the entire plant should be removed including all the root portions. If fruits are present, collect, bag, and dispose of them in heavy garbage bags. Always wear gloves and long sleeves to protect your skin from poison ivy and barbed or spiny plants.
Mechanical Control
Cut climbing vines near the ground at a comfortable height to kill upper portions and to relieve the tree canopy. Vines can be cut using pruning snips or a pruning saw for smaller stems, or a hand axe or chain saw for larger vines. Minimize the damage to the bark of the host tree. Rooted portions will remain alive and should be repeatedly cut to the ground or treated with herbicide.
Cutting without herbicide treatment requires vigilance and repeated cutting because plants will resprout from the base. Begin treatment early in the growing season and repeat the treatment every two weeks until autumn.
Chemical Control
Systemic herbicides like triclopyr (such as Garlon® 3A and Garlon® 4) and glyphosate (such as Accord®, Glypro®, Rodeo®) are absorbed into plant tissues and carried to the roots, killing the entire plant within about a week. This method is most effective if the stems are first cut and herbicide is applied immediately to the cut stem tissue.
Fall and winter applications will avoid or minimize impacts to native plants and animals. Repeated treatments will be required.
Any herbicide applications should be carefully targeted to avoid damage to native, non-target species. If native grasses are intermingled with the bittersweet, triclopyr is better to use than glyphosate because it is selective for broad-leaved plants and will not harm grasses. Follow-up monitoring is required to ensure effective control.
Caution: Applying herbicides to control invasive plants on property you do not personally own requires a pesticide applicator’s license issued by the state. A pesticide applicator’s license is required to use herbicides on public and private conservation lands.
Caution: Any activities in wetlands (from removing invasives by hand or by applying herbicides) may require a special permit under the Wetlands Protection Act and/or your local bylaws. Be sure to contact your local Conservation Commission before you act.
Notice: Mention Of Pesticide Products On This Web Site Does Not Constitute Endorsement Of Any Material.
More Information
For more information on invasive species in Massachusetts, refer to the Massachusetts Prohibited Plant List at https://www.mass.gov/massachusetts-prohibited-plant-list.
Author
Jill M. Swearingen, National Park Service, Washington, DC
References
Dirr, Michael A. 1990. Manual of wody landscape plants: their identification, ornamental characteristics, culture, propagation and uses. Stipes Publishing Company, Champaign, IL.
Dreyer, G. 1988. Efficacy of triclopyr in rootkilling Oriental bittersweet and certain other woody weeds. Proceedings of the Northeastern Weed Science Society Vol. 42:120-121.
Gleason, H.A. and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada, 2nd ed. New York Botanical Garden. pp 328-9.
Harty, Francis M. 1993. How Illinois kicked the exotic species habit. Pp. 195-209. In B.N. McKnight (ed.), Biological Pollution, Indiana Acad. Sci., Indianapolis, IN. 261 pp.
Hutchinson, M. 1992. Vegetation management guideline: round-leaved bittersweet (Celastrus orbiculatus). Natural Areas Journal 12:161.
McNab, W.H. and M. Meeker. 1987. Oriental bittersweet: a growing threat to hard-wood silviculture in the Appalachians. Northern Journal of Applied Forestry 4:174-177.
Shepard, C. 1996. Invasive Plant Information Sheet: Asiatic Bittersweet (Celastrus orbiculatus Thunb.). The Nature Conservancy, Connecticut Chapter, Hartford, CT.
Southeast Exotic Pest Plant Council. 2003. Invasive Plant Manual. http://www.se-eppc.org/manual/bittersweet.html
Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Oriental Bittersweet (Celastrus orbiculatus). http://www.invasiveplantatlas.org/subject.html?sub=3012
The Nature Conservancy. Oriental Bittersweet: Element Stewardship Abstract. In: Wildland Weeds Management & Research Program, Weeds on the Web. http://www.imapinvasives.org/GIST/ESA/
USDA, NRCS. 2009. The PLANTS Database http://plants.usda.gov/ National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
Virginia Native Plant Society. 1995. Invasive Alien Plant Species of Virginia: Oriental Bittersweet (Celastrus orbiculatus Thunb.). Virginia Department of Conservation and Recreation. http://www.dcr.virginia.gov/natural-heritage/document/fsceor.pdf
Species Management and Control Information http://www.docs.dcnr.pa.gov/cs/groups/public/documents/document/dcnr_20027203.pdf
Southeast Exotic Pest Plant Council – Invasive Plant Manual – Oriental bittersweet. http://www.se-eppc.org/manual/bittersweet.html – 2003
Plant Conservation Alliance, Alien Plant Working Group https://www.invasive.org/species/weeds.cfm