Bulletin #2504, Maine Invasive Plants: Japanese Barberry, Berberis thunbergii (Barberry Family)
Developed by the Maine Natural Areas Program and University of Maine Cooperative Extension
Threats to Native Habitats
Japanese barberry has escaped from cultivation and is progressively invading natural areas. It is a particular threat to open and second-growth forests. An established colony can eventually grow thick enough to crowd out native understory plants. Traversing through dense patches of barberry can be difficult and even painful. Birds eat the red berries, thereby spreading the shrub into new areas.
Japanese barberry is a dense woody shrub with numerous arching spine-bearing branches. It usually grows about three feet high, but occasionally reaches up to six feet. A single spine grows off the stem beneath each cluster of small wedge-shaped leaves. Its small yellow flowers are four-parted and can occur alone or in small clusters. Flowers appear in May, and the fruits — red oblong berries — persist on the plant into the following winter. In the fall, the leaves of Japanese barberry turn attractive shades of red and orange. Fall foliage color is one of the reasons this plant has been widely planted as an ornamental.
Japanese barberry is found in old fields, in open woods, on floodplains, on ledges, along power lines, and on roadsides. In Maine, it occurs in thickets, on roadsides, and in open areas. Plants are both sun- and shade-tolerant and invasions of relatively undisturbed woodlands are becoming more common. It grows successfully in a variety of soil types.
Japanese barberry is native to Asia. It was brought to North America in the late nineteenth century and has been widely planted as an ornamental. It has escaped and naturalized (is established and reproducing in the wild) as far north as Nova Scotia, south to North Carolina, and west to Montana. In Maine, Japanese barberry has been documented in five counties. It probably occurs in more, particularly the southern counties, but has been under-collected due to a general lack of interest in weedy species.
Mechanical removal is recommended because it is effective and may cause the least disturbance. Japanese barberry is one of the first plants to leaf out in spring and is therefore easy to distinguish from other shrubs. Whole shrubs may be removed with a hoe or weed wrench. Use of thick or sturdy gloves is recommended to provide protection from the spines. Plants can resprout from roots, so remove as much of the roots as possible. Regular mowing can prevent barberry from returning once it has been removed. In areas where mechanical removal is not practical, such as rock piles or outcrops, a glyphosate herbicide can be used. Consult a licensed herbicide applicator before applying herbicides over large areas.
Josselyn Botanical Society of Maine. 1995. Checklist of the Vascular Plants of Maine, Third Revision. Orono, ME: Maine Agricultural and Forest Experiment Station.
Haines, A. and T.F. Vining. 1998. Flora of Maine. Bar Harbor, ME: V.F. Thomas Co.
The Nature Conservancy of Vermont. 1998. Invasive Exotic Fact Sheet: Japanese Barberry. Montpelier, VT.
Brunelle, H. and B. Lapin. 1996. Invasive Plant Information Sheet: Japanese Barberry. Middletown, CT: The Nature Conservancy of Connecticut.
Gleason, H.A. and Cronquist, A. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. New York: New York Botanical Garden.
For more information or for a more extensive list of references on invasive species contact:
Department of Conservation
#93 State House Station
Augusta, ME 04333-0093
University of Maine Cooperative Extension
495 College Avenue
Orono, ME 04469
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