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Invasive Species: Garlic Mustard

written by: Maricar•edited by: Niki Fears•updated: 5/31/2009

An overview of garlic mustard, a highly invasive weed that is threatening to take over the woodlands of North and Midwestern U.S.

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    The Garlic mustard plant (Alliaria petiolata) is an invasive species that is common in the northeastern and midwestern U.S. Its name is derived from the scent reminiscent of garlic or onion, which is released when the leaves and stems are crushed. It grows as readily in established forests as it does on yards. Garlic mustard typically grows best with some shade.

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    Biology and Method of Spread

    First year garlic mustard Garlic mustard is a biennial herb that could grow up to reach heights of over 4 feet tall. It has scalloped leaves that form rosettes and that stay green through the cold temperatures of winter. In its second year, the garlic mustard plant produces an abundance of white flowers perched on one or two of its stems. The fruits of the plant are up to 2 ½ inches long and contain a single row of black seeds. Ridges on the seed coats allow the seeds to be carried on the fur of animals and in addition to this mode of transportation, the garlic mustard seeds are also easily spread via water.

    Because the seeds are so easily spread, this plant can begin to cover a wide area quite quicklhy. Garlic mustard is a highly invasive species that has taken over portions of the habitats of woodland flowers. If left untouched, it will eventually cover a forest floor, smothering native plants and affecting the balance between local flora and fauna.

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    Second-year garlic mustard 

    Infestations of garlic mustard are best checked when they are small. This is best done before the plant has had a chance to flower and propagate, in the spring. Pulling the plants out of the soil, either manually or using tools, is for small patches of the weed.

    For more significant spreads, burning during the fall or early spring may be done. However, there is a chance that seeds will survive the fire and that new plants will grow even more vigorously. Burning should be repeated yearly for at least 3 years for it to be effective. Herbicides have been used to control large infestations although this is not recommended due to the harm that the chemicals can cause to the environment. Research into methods of biological control is being conducted by a consortium coordinated through Cornell University.