Invasive Species of Concern in Maryland

ANNAPOLIS, MD (October 21, 2004) Mile a Minute

(photo: Britt Slattery, U.S. Fish and Wildlife Service, www. invasive.org)

The name alone says it all - this is one fast growing plant! Mile-a-minute weed (MAM), also known as devil’s tail tearthumb, is an herbaceous, annual, trailing vine in the buckwheat family (Polygonaceae). It is native to Asia and was introduced into the e astern U.S. (York County, Pennsylvania) during the 1930s for ornamental interest. MAM is reported to be a problem in Wisconsin and in nine states in the northeast and mid-Atlantic including Connecticut, Delaware, Maryland, Massachusetts, New Jersey, Pennsylvania, Virginia, West Virginia, and Washington, D.C. It has the potential to spread and establish throughout much of the U.S. These credentials have earned MAM the prestigious spot as “Invader of the Month” by the Maryland Invasive Species Council for October 2004.

Known scientifically as Polygonum perfoliatum, MAM is a sun-loving plant that prefers moderate to full sunlight and moist conditions. It invades forest edges, stream banks, wetlands, roadsides, uncultivated fields, fence lines and other disturbed, open sites. It grows very rapidly, scrambling over low vegetation and up tree branches into the canopy. Thick blankets of MAM vines smother and kill native plants by blocking light and preventing photosynthesis.

The stems and leaves of MAM are armed with downward pointing hooks or barbs which help it hold onto vegetation as it climbs. These barbs also make it difficult to walk through infested areas and painful to remove MAM by hand. The leaves are distinctly shaped like an equilateral (equal-sided) triangle and alternate along the narrow, delicate stems. Like most polygonums, a small collar-like structure surrounds the stem at each node. Flowering begins in June or July and continues through the growing season. The small, light green, inconspicuous flowers are followed by clusters of colorful blue-purple fruits each containing a single glossy, black or reddish-black seed.

Birds are attracted to the colorful fruits of MAM and are apparently its primary long-distance dispersers. MAM seeds are transported locally by ants that are attracted to a small food body on the seeds. The ants feed only on the food body and may help the survival of MAM by inadvertently planting the seeds. Water may also play an important role in dispersal. Its fruits can remain buoyant for 7 to 9 days and may be carried during flood events.

Weevil to the rescue? A biological control agent has been investigated for control of MAM and is planned for a test release into the wild in Delaware. This knight-in-shining armor is a tiny orange weevil with the scientific name Rhinoncomimus latipes that is specific to MAM in China. Adult weevils feed on foliage and the larvae tunnel through the stems, causing defoliation, wilting and death of MAM under heavy feeding pressure.

Small infestations of MAM can be removed by hand while wearing leather gloves, long pants, and a long-sleeved shirt to prevent scratches and cuts from the barbs. Removal of vines before fruits are produced will help prevent buildup and spread of seed. If fruits are present, the vines should be balled up, bagged, and disposed of in a landfill. For practical purposes, large infestations require treatment with herbicide. Controlled areas need to monitored throughout the summer and retreated as necessary. Due to the continual spread of seed, and seed remaining in the soil, favorable sites may unfortunately remain infested for years to come.

For more information about other Invasive Species of Concern, visit www.mdinvasivesp.org or call MDA at 410.841.5920.

photos available electronically on request.