Oriental Bittersweet Identification and Management

By Celestine Duncan, editor

By Celestine Duncan, editor

Figure 1: Distribution of oriental bittersweet (by county) in the United States (EDDMapS 2019).

Figure 1: Distribution of oriental bittersweet (by county) in the United States (EDDMapS 2019).

Oriental bittersweet (Celastrus orbiculatus) is native to Korea, China, and Japan. It was introduced to the United States in the 1860s as an ornamental plant and is still sold for landscaping, despite its invasive qualities. It is currently reported naturalized in much of the eastern half of the United States (Figure 1), and in Ontario and Quebec Canada.

Oriental bittersweet is highly invasive with a wide distribution range. It is most abundant in mesic, mixed-hardwood forests and forest edges, but is also adapted to coniferous forests, riparian woodlands, shrub land, abandoned fields, and coastal beaches and dunes. In full sunlight, oriental bittersweet may grow 10 to 12 feet per year. The vine is shade- and light-tolerant at all life stages.

Identification and Spread

Oriental bittersweet is a deciduous vine (liana) with woody, twining stems that can reach 66 feet in length. The vine uses woody shrubs and trees for structural support, twining around support trunks and branches of desirable vegetation. Vines may eventually over-top and shade out desirable trees and shrubs. Oriental bittersweet assumes a sprawling form on open sites, making impenetrable thickets.

Oriental bittersweet spreads by seed and roots. The vine is dioecious with male and female flowers occurring on separate plants. Leaves are alternate, oblong, from 2 to 5 inches long, and 1.5 to 2 inches wide. Flowers are sparse, occurring in branched clusters (cymes). Fruit are 3-valved capsules about 0.4 inches in diameter. Each valve contains one to two seeds covered by fleshy, yellowish red arils. Seeds and arils mature in autumn and remain on the plant all winter. People collecting vines for wreaths and other fall decorations, and wildlife are important means of long-distance dispersal. Seeds remain viable in soil for about one year.

Asexual regeneration is important for oriental bittersweet spread. It sprouts from roots, root fragments, and the root crown. Cutting or damaging branches, root crowns, or roots encourages sprouting.

Oriental bittersweet has been shown to hybridize with the relatively uncommon American bittersweet (Celastrus scandens L.). Hybridization may lead to the loss of American bittersweet's genetic identity. Differences between native and non-native bittersweet are described at the end of this article.

Photographs of oriental bittersweet (courtesy of Anne Morse, Winona County, MN): (L to R) Oriental bittersweet vine climbing hardwood tree; fruit showing 3-valved, yellow capsule; thicket covering desirable woodland.

Photographs of oriental bittersweet (courtesy of Anne Morse, Winona County, MN): (L to R) Oriental bittersweet vine climbing hardwood tree; fruit showing 3-valved, yellow capsule; thicket covering desirable woodland.

Management

Preventing the introduction of oriental bittersweet is the most cost-effective management tool for managing the invasive species. Once it’s established, early detection and control is critical to stop spread. Click here to read about an eradication program in southeastern Minnesota.

Herbicides

Oriental bittersweet can be controlled with selective herbicides using basal cut-stump or low-volume basal applications. For basal cut-stump treatments, apply Garlon® 4 Ultra herbicide plus basal bark oil soon after cutting to optimize oriental bittersweet control. To prepare the herbicide mixture, make a solution of 25% Garlon 4 Ultra with 75% basal oil (Table 1). Apply the herbicide solution to the sides of the stump, including the root collar area, and outer portion of the cut surface until thoroughly wet, but not to the point of runoff. This herbicide mixture can be applied all year; however, it becomes too thick to spray out at temperatures below 30⁰F.

Low-volume basal (LVB) treatments are well suited for controlling individual woody plants near desirable vegetation or sensitive areas in low-density brush situations. Apply the herbicide solution (Table 1) entirely around the circumference of the stem in a band 12 to 15 inches wide, until the stem is thoroughly wet, but not to the point of runoff or puddling.

Table 1: Low-volume basal or basal cut-stump tank mix guide to control oriental bittersweet with Garlon® 4 Ultra herbicide plus oil-based carrier*.

bittersweet table1.png

Physical or mechanical control

Repeated mowing or cutting every two weeks throughout the growing season may control oriental bittersweet. Young plants can be removed by hand-digging. Stem or roots left on the site may sprout, so plant parts should be collected, bagged, and removed to prevent rooting. Occasional mowing, cutting, or grubbing only encourages root sprouting and is not recommended.

With any treatment method, follow-up monitoring will be needed to control sprouts and newly germinated seedlings.

References:

  • Consortium of Pacific Northwest Herbaria Specimen Database (CPNWH). Available online: www.pnwherbaria.org (accessed May 9, 2019).

  • Dreyer, G., L. Baird, C. Fickler. Celastrus scandens and Celastrus orbiculatus: comparisons of reproductive potential between a native and an introduced woody vine. Bulletin of the Torrey Botanical Club 114(3):260-264; 1987.

  • EDDMapS. 2019. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Available online: www.eddmaps.org (accessed May 8, 2019).

  • Fryer, Janet L. 2011. Celastrus orbiculatus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available online: www.fs.fed.us /database/feis/plants/vine/celorb/all.html (accessed May 8, 2019). 

  • Gage, Karla, S. Flynn, C. Evans, and D. Gibson. 2015. Rate limitation and efficacy trials for low-volume basal bark treatments of C. orbiculatus and L. maackii with aminopyralid and triclopyr. Presentation/data summary.

  • Southeast Exotic Pest Plant Council Invasive Plant Manual. Available online: www.se-eppc.org/manual/bittersweet.html (accessed May 8, 2019)



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