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The Nature Conservancy in Connecticut Connecticut Home Places We Protect Contact News Room Ways of Giving Volunteer Government Relations Corporate Council CLCC Invasive Species |
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Description
Asiatic bittersweet is a non-native woody vine with yellow fruits which split to reveal showy bright red seeds. It is also commonly referred to as Oriental bittersweet. This highly invasive species entwines its round, brown stems about other plants and structures, climbing as high as sixty feet. Approximately two weeks after autumn foliage's peak, the leaves turn golden-yellow and are easily sighted.
Diagnostic information
Roots: outer surface is characteristically bright orange. Stem and branches: round and brown. Flowers: small, greenish-yellow, with 5 sepals and 5 petals, clustered in the axil of the leaves. Fruit: 1/4" diameter, change from green to bright yellow as mature, bright scarlet arils. Leaves: 3/4" to 4-3/4" long and 5/8" to 3-1/4" wide, margin is crenate to serrate, base is cuneate to obtuse, tip is acute to rounded, change from green to golden-yellow as mature.
Habitat
In its native Asia, this species dominates lowland slopes and thickets. Here in North America, Asiatic bittersweet is extremely successful in almost any habitat type, such as disturbed edges, abandoned fields, along coast, and the edge of salt marshes. It prefers utility corridors, fence rows, railroads, and roadways (for example, it is prolific along the Merritt Parkway).
Seasonal Cycle
Asiatic bittersweet is a deciduous perennial plant. There are typically separate male and female plants, which bloom in May and June. Bees aid in pollination. The fruit (on the female plant) ripens by September and remains on the vine through winter. Numerous bird species, such as black-capped chickadee, northern mockingbird, European starling (non-native), and blue jay, small mammals, and human activity (such as composting ornamental cuttings) widely disperse the Asiatic bittersweet's seeds. Rootsuckering, the ability to send up shoots from the roots, contributes to the vine's high density once established at a site.
Distribution
Asiatic bittersweet is native to temperate East Asia (Japan, Korea, and China). Introduced to North America in the mid-nineteenth century, it quickly became established from Louisiana to Maine. Asiatic bittersweet reached Connecticut as early as 1916 as an ornamental and is now found throughout the state.
Threat
Due to its high reproductive rate, long-range seed dispersal, and rootsuckering abilities, Asiatic bittersweet can quickly disperse through an entire area, threatening upland meadows, thickets, young forests, and beaches alike. Growth of native vegetation is extremely limited beneath bittersweet's dense shade, and it tends to strangle small trees and shrubs by growing around their stems, constricting the flow of the plant's fluids. Many supporting plants also succumb to wind and ice storms with the added weight of the vine. Asiatic bittersweet also has the capacity to hybridize with the native American bittersweet (Celastrus scandens), cross-pollinating to the extent of modifying the genetic differences between the two species.
Control
The Nature Conservancy and project partner the Connecticut Agricultural Experiment Station recently conducted research on the control of Asiatic bittersweet at Bluff Point, in Groton, funded by the DEP License Plate Fund (project completed in Fall of 2006). Included in this research were herbicide treatments, applied to the basal bark of vines, as well as applications to cut stumps, near ground level. These applications were done using a foam paint brush, not from a spray. Different concentrations of the chemicals glyphosate (Roundup is one product name) and triclopyr (Brush-B-Gon) were used for each treatment.
In general, the cut stump treatments were more effective than the basal bark treatments in reducing the number of living bittersweet vines the year after treatment application. Higher concentrations of either herbicide generally provided better control. A Roundup formulation with a 25% active ingredient of glyphosate performed well. (Note: any herbicide use must adhere to the label instructions on the product) Both small and large Asiatic bittersweet vines were treated, but vine size did not seem to affect treatment response in terms of survival the following year, number of sprouts or sprout length. The spring and summer herbicide application timings appear to have been more effective than the fall timings. Carefully applying an herbicide directly onto cut stumps will minimize impact to “non-target” species that are adjacent to the vines you are treating.
For more details on this research, please contact the Connecticut Chapter.
Low patches of bittersweet can be removed by cutting the vine and applying triclopyr herbicide (the active ingredient in Ortho's Brush-B-Gone®) to the regrowth a month later. Care must be taken when cutting an area infested with bittersweet, to protect native plant species still in the area, as these plants will help ensure the treated area is revegetated. Asiatic bittersweet has a substantial seed bank, and successful removal of the species requires perseverance through two or three years.
Other Points of Interest
Asiatic bittersweet is similar in appearance to the native species American bittersweet. Asiatic bittersweet is distinguished from American bittersweet by the fact that its fruit and flowers are located in clusters of three to seven in the axil of the leaves (between the leaf and the stem). American bittersweet's fruit and flowers are located at the branch tips only. It is very important for land managers, naturalists, and gardeners to distinguish between the native species and the invasive species in any control efforts.
Asiatic bittersweet was planted for wildlife food and cover, cultivated to use the fruit-covered vines for decorations, and employed in soil erosion control.
Nature picture credits (top to bottom, left to right): Photo © Chris Evans, River to River CWMA, Bugwood.org (Bright Red Seeds of the Asiatic bittersweet (Celastrus Orbiculatus)); Photo © Chris Evans, River to River CWMA, Bugwood.org (Asiatic bittersweet (Celastrus Orbiculatus)).
