by Bruce Wenning
Family Celastraceae. Genus Celastrus. Species Celastrus orbiculatus Thunb.
Regulations: The importation, distribution, trade, and sale of Asiatic bittersweet vine have been banned in Massachusetts effective January 1, 2009 (Massachusetts Prohibited Plant List website, 2012).
General Description: Asiatic bittersweet is a deciduous vine with alternate, simple, obovate to orbicular (round in shape) leaves with slightly toothed (crenate-serrate) margins (Dirr, 1998). Leaf apex has a slightly pointed tip (Dirr, 1998; Zheng, et al, 2006; Magee and Ahles, 2007). Asiatic bittersweet originates from China, Japan and Korea (Zheng et al, 2006; Huebner, Olson and Smith, 2006).
This exotic invasive vine effectively utilizes nearby trees, shrubs, or any other above ground structure as scaffolding that helps it to grow upward into sunny exposures using its twining stems. As witnessed on many trees, the growth habit of this vine typically wraps around tree trunks as it grows upwards where it eventually constricts the host plant’s vascular system, thus inhibiting carbohydrate flow from the leaves to the roots and water and nutrient flow from the roots to the leaves and above ground growing points. Eventually, the host plant weakens and slowly dies from a combination of the vine’s rapid shading and vascular (phloem and xylem) constriction; branches die and break off; roots weaken and the host tree may topple over (Fryer, 2011; Ellsworth, 2005). Infested host trees are particularly susceptible to snow, ice and/or wind storms.
If you observe areas that are heavily infested with this vine, you will notice that the growth habit of twining is characteristic of the species and very effective for its survival. In the absence of a structure to climb upon, this vine will use its own twining stems to grow toward the light creating impenetrable thickets in open fields and other areas where there is no other available scaffolding. I have seen this species send up multiple stems that wrap around each other to gain enough rigidity to span into areas too distant for a single vine. Eventually, the wrapped stems contact a very distant branch or tree.
The orange-colored roots serve as a diagnostic identification characteristic observed when one pulls out seedlings as well as adult plants. Young vine stems have warty lenticels on light brown colored bark (Somers, Kramer, Lombard, and Brumback, 2006). Older vines exhibit a gray / brown colored furrowed bark.
Asiatic bittersweet vine exhibits the following invasive traits:
(1) High seed production and good seed viability. Reproductively mature vines are prolific seed producers primarily in sunny areas. Seed has a high viability to germinate, particularly in the first year of production (Fryer, 2011; Ellsworth, 2005). Ellsworth (2005) stated that from his research and experience approximately two-thirds of first year seed that contacts soil actually germinates the year it is shed when environmental conditions are right. Seed viability drops considerably in the second year (Ellsworth, 2005; Fryer, 2011). Seeds that become part of the soil seed bank show a reduction in viability after the first year; seed bank longevity for this species is short-lived in most soil and site conditions (Ellsworth, 2005; Fryer, 2011). According to Fryer (2011), some land managers have noticed that small portions of viable seed germinated in seed banks older than one year. Seeds are a deep red-purple color embedded in red-colored arils (i.e. fleshy seed tissue) surrounded by orange and yellow capsules (Somers et al, 2006; Dirr, 1998).
(2) Vectors. Seed is dispersed by birds and other berry-feeding animals, sometimes over great distances; wind and water are less effective at dispersing seed. The combination of this species’ seed production and viability with the continuous spread by birds makes this vine an effective and efficient invader of residential properties, local landscapes, and larger surrounding ecosystems (Ellsworth, 2005). The vector trait provides an advantage for rapidly colonizing new and especially far away sites.
(3) Sexual reproduction breeding system. Asiatic bittersweet vine is dioecious [i.e. having male and female flowers (reproductive parts) on separate plants]. Male vines have flowers that produce pollen. Pollen fertilizes a female vine flower that produces fruit and seed. Both male and female plants need to be in close proximity in order to successfully reproduce. Pollination occurs by bees, other insects, and wind. This may help explain why, as an early colonizer, this vine forms randomly distributed and dense populations or patches that appear to “leapfrog” through a woodland (or neighborhood) over time. When left unchecked, these populations can join each other or coalesce forming contiguous populations throughout a property, larger landscape, or region of land overlapping many different types of landforms and/or ecosystems and simultaneously exhibiting different age classes (younger and older vines) growing together. In addition, many ecologists are concerned that Asiatic bittersweet vine hybridizes with the American bittersweet vine (C. scandens), thus diluting the native species gene pool (Dirr, 1998; Somers, et al, 2006).
Side note: Asiatic bittersweet vines that grow as single vines in the woods with no further seed production/germination could be a lone male or female vine deposited by a bird far from the original (dioecious) breeding population, or the vine may be growing under shady conditions. When an opposite sex vine comes in close proximity, the lone vine or new arrival could then produce berries and eventually start a viable, reproducing invasive population (i.e. the leapfrog effect mentioned above) that could add to new populations in the existing area or infest new areas via vectoring birds.
(4) Vegetative or asexual reproduction (i.e. sprouting). Vegetative reproduction occurs when stems are cut or broken. For both male and female vines, sprouting produces more reproductive stems than the original uncut or unbroken stem. Asiatic bittersweet produces new stems from root sprouts as well as from root fragments left behind by incomplete pulling and/or digging (Fryer, 2011; Ellsworth, 2005).
(5) Predator avoidance and/or deterrence. There are virtually no appreciable predators or diseases feeding on this plant to curtail its growth, development, and spread.
(6) The timing of leaf out and leaf loss. Leaves emerge in the spring with other native plants; however, this species holds onto its leaves a little longer in the fall than most native plants. This trait contributes to Asiatic bittersweet’s ability to produce more carbohydrate and other compounds in the leaves by way of photosynthesis and to transport these products to the roots for storage (i.e. cold weather storage for better winter survival and spring growth).
(7) Sun/shade tolerance. Asiatic bittersweet is shade tolerant. However, like glossy buckthorn and common buckthorn, it frequently invades sunny areas which is why it is seen growing in open fields; along field, road and, path edges; and in any other areas that are sunny. Ellsworth (2005) stated that Asiatic bittersweet has the genetic variability to tolerate a wide range of sun and shade exposures; high seedling survivorship was observed under deep shade; however, he also noticed that partially shaded conditions contributed to high seedling survivorship.
Ellsworth as cited in Fryer (2011) reported that the thickness of the woodland litter layer affected seedling emergence; seedlings of Asiatic bittersweet were more successful emerging from pine litter layer than thick oak litter. Pine litter has a structure more conducive to air and light penetration than the heavy matting effect that results from overlapping oak leaves.
(8) Time of year of fruiting. Asiatic bittersweet flowers from May to June; flowers are a greenish-yellow color (Zheng, et al, 2006). Flowering time is the same as for common buckthorn. However, the fruiting period is quite long, beginning in July and lasting through October (Zheng, et al, 2006). Like other exotic invasive plants this species has fruiting periods that are longer than most native plants in the landscape which increases its invasion success.
IPM Control Strategies for Asiatic Bittersweet Vine
1. Cultural Controls: Monitor or visually inspect your property for Asiatic bittersweet. Do this at least every June and September. As stated in Part II of IPM Control Strategies for Exotic Invasive Plants, prevention is a cultural control of great value. Do not plant, transplant, or encourage the planting of this species. Do not use this vine in the fruiting stage in holiday decorations particularly Christmas wreaths. Educating others (e.g. clients or neighbors) about the dangers of this pest is another cultural control of enormous value.
2. Mechanical Controls: Pull, dig, and cut. Pull out easy-to-pull plants. If you can’t hand-pull Asiatic bittersweet, then you can dig out the plant. Attempting to pull it out with a Weed Wrench ® can prove to be troublesome for many people because the woody stems have a spongy or soft construct (less rigidity) than other woody plants. Spring or early summer cutting will slow its growth and reduce its ability to form functional male or female flowers for reproduction. Remember, this species is a dioecious plant with male flowers on one plant and female flowers on another plant. Cutting down Asiatic bittersweet vines in close proximity to one another before they flower disrupts an otherwise intact breeding system. In addition, the practice of repeated cutting on a monthly or so basis will be more effective at stunting the plant and inhibiting flower and fruit production.
Mechanical controls can be done at any time of the year; however, the best times are the months before or during flowering. Vines that have been cut at the base but are very large or entangled in the host vegetation should be left hanging in place for three to six months before they are pulled down. Freshly cut vines have a spongy or soft construct to their woody stems and need to dry out to become brittle enough to be easily pulled down without damaging host branches.
3. Biological Control: There are no insects, mites or commercially available disease organisms yet found to be effective biological control agents.
4. Chemical Controls: The best time for any control option is just before a plant flowers. In addition, the application of herbicides in July, August, and up to mid-September gives maximum chemical control. These are the months that carbohydrates and other plant compounds are being manufactured in the leaves by way of photosynthesis and transported from the leaves to the roots for storage. This downward flow of plant compounds helps facilitate the transport of foliar and stump applied herbicide to the roots during these months for more effective kill. The mechanical control of cutting or mowing is also very effective during these months for the same reason. For example, when you cut the top off any plant the roots naturally respond by pushing up more top growth (sprouting), reducing the root reserves (carbohydrates and other growth compounds) stressing the plant. Every time you cut the top off you force the plant to sprout which reduces the root reserves and weakens the plant.
Suggested chemical control for vines too difficult to hand pull or dig during July, August, and up to mid-September is to cut Asiatic bittersweet down to one inch from the ground and immediately apply straight glyphosate herbicide to the freshly cut stump using a paint brush or sponge applicator. Roundup ‘poison ivy killer’ works very well. Suggested chemical control in March, April, May, and June is to cut the stump high (six to twelve inches) and let it sprout. Then cut the sprouted plant in July, August, or early September to one inch from the ground and immediately stump-applicate with straight glyphosate herbicide.
A Suggested Asiatic Bittersweet Vine Example Using the IPM Procedure
1. Properly identify Asiatic bittersweet vine. Educate your neighbors and others about what you are doing and why.
2. Hand pull (or cut) what you physically are able before Asiatic bittersweet produces berries (seeds), preferably before September.
3. Using a Weed Wrench® on hard to pull plants is, at times, not practical.
4. Plants that prove to be too difficult to remove by way of pulling or digging you can cut down to a one-inch stump and immediately apply a glyphosate herbicide to the freshly cut stump using a paint brush or sponge applicator. Stump application is very effective during July, August, and up to mid-September. Remember, you may have to leave the remaining vine up into the host vegetation because the vine has to dry out to become brittle enough to be effectively pulled off the host without causing branch damage.
If you cannot stump-applicate the hard to pull plants during the summer months, then you can instead cut the plant six to twelve inches from the ground before it starts to produce berries (seeds) preferably by September (Ellsworth, 2005). After the taller stump has re-sprouted, you cut it to one inch above the ground and immediately apply glyphosate herbicide to the freshly cut stump. Allowing the stump to re-sprout during the summer months draws carbohydrate and other growth compounds from the roots and depletes some of the root energy making herbicide kill more effective.
5. Foliar application of glyphosate works best on multi-stemmed vines that had been repeatedly cut for many years without chemical control follow up or had not been removed by digging. Foliar application works best between July and mid-September particularly on impenetrable thickets growing in open areas such as fields, along road sides and paths where the vines are not growing up on host vegetation. Foliar application transports the herbicide from the leaves to the roots. If Asiatic bittersweet has many stems with foliage and is quite large, it may take one to two years for complete kill after one foliar application because multiple stemmed specimens generally have a very large root system. Climbing vines that have foliage close to the ground should be sprayed from the ground up to six or more feet for effective control. If vines have a small amount of low level foliage and / or are too tall with no available low foliage then stump applied herbicide would be more effective. Individuals contemplating using chemical control of Asiatic bittersweet in or near wetlands must use a wetland approved herbicide. It’s the law.
6. Cold weather stump application (November through February; temperatures ranging from 15.8 to 46.4 Fahrenheit) (Reinartz, 1997) reduces the risk of contaminating non-target plants. University of Wisconsin researcher, James Reinartz (1997), tested cold weather stump application using 25% concentration of glyphosate herbicide on glossy buckthorn and obtained 92 to 100% control. I have used straight glyphosate concentration on the freshly cut stumps of Asiatic bittersweet vine in November and obtained a 98 % kill in a small, but heavy, infestation of vines that were between two and four inches in diameter. Cold weather control frees up time for control efforts that is not available during the summer months and is especially useful on overgrown Asiatic bittersweet individuals.
7. The above suggested example may be modified to suit existing site conditions and the level of Asiatic bittersweet vine infestation.
To learn more about Asiatic bittersweet vine, visit: www.invasive.org.
For additional information about exotic invasives, refer to Bruce’s article: “Controlling Small Scale Infestations of Exotic Invasive Plant Species: Ecological and IPM Information for Landscapers and Homeowners.”
Individual Exotic Invasive Plant Fact Sheets:
About the Author
Bruce Wenning has university degrees in plant pathology and entomology and is an ELA Board member and regular contributor to the ELA Newsletter. Bruce also spearheads the effort to expand ELA’s website content. Watch for his upcoming articles with information about individual invasive species. He is a horticulturist at The Country Club, Brookline, MA where he continues his battle with exotic invasive plant species.