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Garlic mustard - serious invader from the East
by Mike Owen

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May 26, 2000 - Iowa State University has recently received numerous inquiries about a relatively new invasive weed problem. The weed is garlic mustard (Alliaria petiolata) and invades woodlands, parks, and "natural" plantings. Garlic mustard is extremely aggressive and will rapidly displace native forbs and wild flowers. This plant can eventually become the dominant species in woodlands and parks and will develop in dense stands. Garlic mustard spreads as a uniform advancing front from established infestations but will also move quickly over greater distances as a satellite population when introduced into new areas accidentally by man or animals.

Garlic mustard is a biennial and thus requires two years to complete a life cycle. The first year, seeds germinate early in the spring and grow as a basal rosette. The plant over-winters and begins to flower later in the second spring. Seed production is quite high and seeds are dormant thus enabling them to remain viable in the soil for many years. Garlic mustard was introduced from Europe, presumably as a plant with medicinal properties. When species are introduced into new areas, often the new habitat does not have the ecological "checks and balances" of the native habitat and the introduced species will grow unimpeded.

Garlic mustard is in the Cruciferae plant family. Crucifers have flowers with four petals arranged in a cross. Garlic mustard flowers are white and occur in the second year in clusters at the top of the stem. Plants have a distinct and strong garlic odor and can grow as tall as three to four feet. Fruits are slender capsules called siliques that are 1 to 2.5 inches in length. Seeds are oblong, black and occur in a single row within the silique.

Control strategies are somewhat limited and must reflect the location of the garlic mustard infestation. There are effective mechanical, cultural and chemical tactics available for garlic mustard management. Mechanical tactics include hand-weeding and decapitation of the flower stalk. If hand-weeding is used, most of the root must be removed to prevent resprouting. Further, hand-weeding also causes considerable disturbance of the desired native flora and thus maybe be to destructive in sensitive areas. Removing the flower stalk soon after flowering begins will effectively eliminate seed production, and if cut at the soil surface, plants will not resprout.

Burning in the early spring or fall is a cultural tactic for garlic mustard management. However the fire must be hot enough to burn away all exisiting vegetation. Fall burns seem to work more consistently, but the treatment will be needed for several consecutive years for best control. Plan to supplement burning with hand-weeding.

There are several herbicides that have activity on garlic mustard. These include glyphosate (Roundup), sulfosate (Touchdown), triclopyr (Garlon), and 2,4-D. A combination of 2,4-D and triclopyr is also available (Crossbow). The use of herbicides is difficult in areas where there is desirable wild flowers or other forbs. Spot applications of glyphosate/sulfosate as a 1 or 2% solution will be effective and serve to keep the herbicides off desirable species. Otherwise, apply herbicides when the desirable plants are dormant. Be sure to follow the label instructions for all herbicide applications.

Links to other garlic mustard information:

Prepared by Mike Owen, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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Common chemical and trade names are used in this publication. The use of trade names is for clarity by the reader. Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply nonapproval.