It is that time of year when certain invasive plants come into blazing fall color. One of those plants is Oriental bittersweet (Celastrus orbiculatus). Its yellow fall foliage can be seen twining around trees and shrubs and its stems are laden with bunches of bright yellow and red berries - often sought after for use in wreaths and floral arrangements.
Although seemingly harmless in a decorative arrangement or when covering a garden trellis, Oriental bittersweet is very harmful in natural areas. It thrives in open, sunny sites such as forest edges, fields and hedgerows, but its tolerance for shade allows it to also invade woodland areas.
This invasive ornamental is a vigorously growing woody vine with alternating leaves that are somewhat glossy and nearly as wide as they are long (round), with finely toothed margins; stems can reach lengths of 60 feet and thicknesses of 4 inches. It climbs over and smothers vegetation which can 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. Infestations can also accelerate forest fires; vines enable flames to quickly travel from the ground to the forest canopy.
The autumn infestation of Oriental bittersweet
Oriental bittersweet leaves
Oriental bittersweet berries
Oriental bittersweet also threatens American bittersweet (Celastrus scandens) by displacing it through competition and hybridization. These two species closely resemble each other, but the native bittersweet does not exhibit aggressive growth, though when it hybridizes with Oriental bittersweet it too can become problematic.
Oriental bittersweet is a prolific seed producer. It has small, inconspicuous flowers that develop in the spring where the leaves join the stem (axils). Fruits are round and green when young and ripen to yellow and split to reveal showy, scarlet berries that persist into winter. The location of the berries is an important identifier of the species. American bittersweet has flowers and fruits only at the ends of branches (terminal), rather than in the leaf axils.
Introduced from East Asia in the 1860s, Oriental bittersweet has since invaded natural areas from Maine to Louisiana and west to Iowa, yet it is still widely planted and maintained as an ornamental vine, further promoting its spread. Even if a landowner contains its growth in a garden setting, it can still be dispersed widely and quickly due to birds eating the berries and spreading the seeds. If the plant is near water, the fruit can float and be moved downstream. The plant can also spread vegetatively by root suckering.
Dense infestations blanket trees along I-87, I-90 and I-787 in Albany, forming living walls. Unfortunately it has already made inroads into the Adirondack region and infestations are gaining ground in Lake George, Saranac Lake and Star Lake, among others. Manual, mechanical and chemical techniques are all effective methods of control, depending on the extent and type of infestation, the amount of native vegetation on the site, and the time, labor and other resources available to you.
To report infestations in natural areas or learn more about best management and disposal practices, please contact the Adirondack Park Invasive Plant Program at 518-576-2082 x 131. Also remember that if purchasing bittersweet at nurseries, confirm that the variety you are buying is American bittersweet (C. scandens) and not the invasive one (C. orbiculatus).
'Eye on Invasives' is a biweekly column that spotlights a top invader when it is easiest to identify. The Adirondack Park Invasive Plant Program is a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley. Find out more about this award-winning program online at www.adkinvasives.com.