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Garlic Mustard Alert: Have You Seen This Villain?

by Rachel Shaw

Garlic mustard (Alliaria petiolata) is an exotic species of European origin that is rapidly invading woodlands in the eastern and central U.S. This pungent biennial, a member of the mustard family, gives off the odor of garlic or onion when crushed. Woodland invaded by garlic mustardIn Europe it is used as an herb or salad green and is believed to have been brought to this country for that purpose. (Garlic mustard is actually featured as an herb in the kitchen garden at Greenfield Village. While this display is probably historically accurate, it indicates that the nature of this invader is not yet widely enough recognized!)

In the first year, plants reach a height of only a few inches, and may be hidden under dead leaves in spring. First year leaves are kidney-shaped and form a basal rosette. The basal leaves are retained in the second year, and differ in shape from the triangular second-year leaves, which are alternate on the stem and become smaller towards the top of the plant. Garlic mustard flowers in the second year and can reach a height of 2–3 feet or more, although some second-year plants may remain quite small. The small white flowers have four petals and are clustered at the top of the stem. The seeds are contained in green pods and are dispersed when the capsules burst open in the fall. Plants retain their green color throughout the winter.

Unlike many weeds, garlic mustard is shade-tolerant. It can quickly come to dominate the forest floor, growing in dense stands and displacing native woodland wildflowers. In less than a dozen years, garlic mustard is capable of virtually eliminating some spring wildflower populations. Garlic mustard seeds appear to spread rather easily via animals, humans, and flowing water. The species often invades along trails or streams.

Eradicating garlic mustard is difficult. Repeated hand pulling or cutting until the seed bank is exhausted may halt its spread in small areas. Pulled or cut plants should be bagged and removed. Burning, and use of the herbicide Roundup, can also be effective. Burns may need to be conducted for at least two consecutive years, as a one-time burn can actually increase seedling production. The use of Roundup is effective but is best undertaken outside of the regular growing season to minimize the impact on other plants. Learning to recognize garlic mustard, pointing it out to others, and taking steps to control it are vital if we are to protect our native woodland flora.

Article reprinted from the Summer 1999 issue of the Ann Arbor Wild Ones Newsletter. Copyright © 1999 Wild Ones–Natural Landscapers, Ltd.

For more information...

...and photos of garlic mustard, see the following web sites:


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