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Invasive Species of Concern in Maryland
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May 2003

Colonial Medicine Herb Plasters the Woods with Mustard
Garlic Mustard
Garlic Mustard
Photo: Jil M. Swearingen, USDI National Park Service, Bugwood.org

ANNAPOLIS, MD (May 8, 2003) – In the 1880’s, settlers brought the Garlic Mustard (Alliaria petiolata) plant from Europe to the New World, to use for medicine and as a flavoring agent in soups. But this plant, named by the Maryland Invasive Species Council as May’s “Invader of the Month,” proved to be more like a disease than a medicine because of its rapid spread and subsequent negative impact on native eastern U.S. plants and animals.

A little more than 100 years after its introduction, Garlic Mustard is widely recognized as a problem by biologists and natural resource managers. The Maryland Invasive Species Council (MISC) hopes to raise public awareness about the problems it and other invasive species through its “Invader of the Month” program.

Garlic Mustard was introduced into New York state, and has spread as far away as Georgia, Canada, Kansas and Nebraska. It is found throughout Maryland, especially in moist, shady woods and along streams. It competes with and crowds out native spring wildflowers such as spring beauties, ginger, Dutchman’s breeches, trillium and toothworts. The toothworts (Dentaria species), which are also mustards, are the primary food source for the rare West Virginia White butterfly (Pieris virginiensis). West Virginia White Butterfly eggs laid on garlic mustard rather than Dentaria fail to hatch.

The spread of garlic mustard is due mostly to activities of humans and animals. White-tailed deer, for instance, prefer native plant species that grow along side Garlic mustard, leaving the mustard to spread without interference.

Once established, Garlic mustard can be difficult to eradicate. For small, new infestations, hand removal of the entire plant including the roots is an effective way to control the spread. Eliminating mature plants can be difficult and require a multi-year commitment since released seeds can remain viable in the soil for up to five years. Mature plants should be weeded, bagged, and removed rather than simply left on site. Chemical applications of glyphosate herbicide (i.e. Roundup) are effective at removing Garlic Mustard plants but should only be used with the assistance or consultation of a natural resource specialist. Researchers are currently studying several insects as potential biological control agents for this troublesome plant.

Garlic Mustard is a biennial plant, completing its life cycle in two years. It germinates in the spring, and forms a basal rosette with kidney-shaped leaves that stay green year round and produce a garlic odor when crushed. In April and early May of its second growing season, the plant shoots up, sometimes as tall as 4 feet. The tall stems have triangular leaves and clusters of small, white four-petaled flowers appear at the top. By June, long string-bean shaped seed capsules called “siliques” form, branching out from the main stem like a skinny candelabra. The seeds inside, which can be thrown far from the mother plant when the siliques explode open, are shiny, slender, black oblongs, a little bigger than poppy seeds.

For more information about Garlic Mustard and other Invasive Species of Concern, visit www.mdinvasivesp.org or call the Maryland Department of Agriculture at 410-841-5920.

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