Contact: Kerrie Kyde, Maryland Department of Natural Resources | firstname.lastname@example.org
ANNAPOLIS, MD (November 14, 2005) – A beautiful, fragrant blooming woody vine from Asia, Japanese honeysuckle (Lonicera japonica) was introduced into Long Island, NY in 1806 as a garden plant and bank stabilizer. Although initially slow to spread, by 1912 this perennial vine had escaped from cultivation, and by 1919 was recognized as a “ruthless invader.” Japanese honeysuckle has proved an aggressive and adaptive addition to the U.S. flora and is now present in the entire continental U.S. except for the Pacific Northwest and the northern Plains states, as well as in Hawaii and Puerto Rico. In mid-fall, as native plants lose their leaves, the semi-evergreen honeysuckle is still highly visible, which is why MISC chose the species as the November Invader of the Month.
Japanese honeysuckle is a woody vine that climbs by twining around trees, drapes over lower shrubs, or sprawls across the forest floor. It has opposite oval to oblong leaves that most often are not toothed or lobed and have a blunt pointed tip, although as a new seedling, Japanese honeysuckle may have lobed leaves that look like small white oak leaves. The familiar fragrant flowers bloom from late April through June in the mid-Atlantic, but sometimes flowers appear as late as October. The flowers are creamy white and turn yellow as they age. Shiny black berries containing two to three dark brown seeds develop in pairs at the nodes in the fall. Younger vines have tight finely haired bark, while older vines have rough shredding bark.
A highly adaptable plant, Japanese honeysuckle invades forests, field edges, disturbed areas, roadsides and floodplains spreading both vegetatively and by seed. It does not usually invade mature closed canopy forests, preferring more sunlight, but can establish in tree-fall gaps or along woodland trails. Once established, it grows rapidly, scrambling over and smothering native herbs and shrubs. Twining up trees into the canopy, it can actually girdle adult trees by twisting so tightly that the supply of water and nutrients is cut off. Trees are also damaged or killed when the vines are so dense they block light to their leaves or pull them down by the sheer weight of the vines. The prolific vine can suppress native tree seedling generation and reduce native herbaceous growth. It competes directly above-ground for light and below-ground for nutrients and space. The seeds are eaten by both birds, including robins, turkeys, quail, bluebirds and goldfinches, and mammals, which furthers its spread. White-tailed deer browse on it, and may contribute to its spread by dispersing the fruit.
In most of Maryland, Japanese honeysuckle is semi-evergreen, and can even hold its leaves throughout the entire winter. It can grow, slowly, at temperatures just above freezing. These characteristics enable the plant to continue to photosynthesize and grow well into the winter, long after native deciduous vines such as Virginia creeper and grapes have lost their leaves. It also gives honeysuckle a jump-start in the spring, when the plant begins to grow as soon as temperatures begin to rise, before native leaf out.
Japanese honeysuckle, including the especially aggressive variety Hall’s honeysuckle (Lonicera japonica var. halliana), is still widely sold as a garden ornamental or for covering walls, fences and steep banks. It can be a beautiful garden plant, but once escaped, becomes a damaging invader in natural areas.
The best way to control Japanese honeysuckle is not to let it get established in the first place. Small plants can be pulled or grubbed out relatively easily. Larger sprawling vines may be removed with a weed wrench or similar tool. However, other tactics are needed for larger and more established infestations, including use of commonly available herbicides such as glyphosate (RoundUp, Rodeo, etc) applied any time from spring through fall when the plant is actively growing.
Photots: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
For additional information about specific control tactics go to:
http://www.nps.gov/plants/alien/fact/loja1.htm which is part of the National Park Service's "Weeds Gone Wild" web site.
For more information about Invasive Species of Concern, visit the Maryland Invasive Species Council.