Controlling Oriental Bittersweet

By Donna Ellis, Senior Extension Educator

This article was originally published in a longer format in the Eastern CT Forest Landowners Assn. Newsletter 39(1):1-3; 5.

Connecticut’s fields, forests, suburban backyards, and urban parks are under threat, imperiled by non-native plants from the faraway continents of Europe and Asia or in some cases from other regions of the U.S. Invasive plants are a problem because they establish easily and grow aggressively, disperse over wide areas, displace native species, and reduce biological diversity. These plants invade not only terrestrial habitats but water bodies as well, where they can grow and proliferate undetected for many years. Some invasive plants are more newsworthy because of their beauty (purple loosestrife), their poisonous traits (giant hogweed), or homeowner frustrations trying to control them (Japanese knotweed).

How do we reduce the harmful environmental impacts of woodland invasive plant species? Let’s talk about one of the most troublesome woodland invaders, Oriental bittersweet (Celastrus orbiculatus), also known as Asiatic bittersweet. Oriental bittersweet was first confirmed in Connecticut in 1916 and today can be found in all towns statewide. Originally from Eastern Asia, this species was first introduced in the US in the 1860’s as an ornamental.

The woody vines of Oriental bittersweet, with reddish-orange roots begin as small, sometimes unnoticeable seedlings in the forest understory. Within several years, if their growth is undetected the young vines will develop from a tangled mass growing along the forest floor to wrap around desirable vegetation: trees and shrubs, or any other vertical structure they encounter. The alternate leaves of Oriental bittersweet are rounded (orbicular; as described by the genus), with fine teeth or serrations along the edges. Clusters of small greenish flowers are produced on female vines in May, followed by the development of red, succulent fruits (ovaries) enclosed in a yellow covering (the ovary wall) that splits open when fruits mature. The fruits consist of three fleshy arils encasing several seeds each. Oriental bittersweet fruits are fed upon by birds and other wildlife in the fall and winter, and the seeds disperse to new locations with the movement of wildlife.

How can Oriental bittersweet be successfully controlled? There are several options for management of this invasive, with the greatest successes occurring when

control begins early and woodlands are monitored for several years. Learn to recognize what young seedlings look like, and they can be easily hand pulled during the first year or two of growth. I make a point of walking through the wooded sections of my property several times during the summer and fall and pull up Oriental bittersweet seedlings, which I typically find under conifers and other trees where birds roost. If vines have been growing undetected for many years and you have dense, woody vines wrapped around desirable vegetation, cut out a section of the vine (several inches in length) in late summer to early fall, separating the top growth from the crown and roots. This mechanical control method will stress the vines and force the plants to use up food reserves in the roots to develop more shoots, and the top growth will die and slowly break down. You will need to continue to cut any regrowth that forms from the crown for several years, but if this method is practiced diligently it can be successful.

A chemical control option is the “Cut and Paint” method, which should also be done in late summer to early fall. Make a similar cut in the vine as described above, and within 20 to 30 minutes, carefully apply a concentrated herbicide (triclopyr products are most effective with woody invasives) to the lower cut surface with a paint brush or other applicator, reading and following all directions on the herbicide label. Avoid making herbicide applications on rainy or windy days, and be sure to avoid herbicide runoff onto the forest floor or onto non-target vegetation. Monitor control sites the following year, and if necessary, repeat the Cut and Paint procedure.

Visit the Connecticut Invasive Plant Working Group (CIPWG) website (www.cipwg.uconn.edu) for information on invasive plant topics that include identification, management, the Connecticut state list of invasive plants, a photo notebook with a gallery of invasives, non-invasive alternative plants, legislative updates, and a calendar listing invasive plant management events and other outreach activities. CIPWG is a consortium of individuals, members of environmental organizations, and affiliates of municipal and state agencies whose mission is to promote awareness of invasive plants and their non-invasive alternatives.