Garlic mustard (Alliaria petiolata) is a major weed in many areas of Illinois. Information from the Illinois Department of Conservation shows garlic mustard scattered throughout the northern three-fifths of Illinois, mainly along stream corridors. This rapidly spreading forest weed is displacing native woodland wildflowers. Garlic mustard is not a weed to take lightly; if you have it, control is imperative. Large expanses of this weed have choked out native plants at Allerton and Lodge parks in central Illinois; there are also large patches in The Morton Arboretum in northern Illinois.
In Illinois, garlic mustard behaves mostly as a biennial. After germinating in the spring, the plant spends its first summer and winter as a rosette of heart-shaped leaves (two to eight inches long) with course, round, irregular teeth on the margins. The following spring, the plant sends up a one- to two-foot flowering stalk of small, four-petaled, white flower clusters.
The plant spreads exclusively by seed, dispersed on the fur of larger animals such as deer, by flowing water, and by human activities. Some plants produce as many as 8,000 seeds! Therefore, the goal of any garlic mustard control program is to prevent seed production until the seed bank is exhausted--usually a two- to five-year period. Cutting and hand-pulling may be feasible with smaller outbreaks; controlled burns and herbicides may be needed for more established patches. Roundup (glyphosate) works best in the spring and fall when the plants are actively growing.
(Adapted from Illinois Garlic Mustard ALERT, IDOC)