Garlic mustard (Alliaria petiolata) is an invasive weed throughout much of the Midwest and Northeast. It forms large patches that overtake native plants. Garlic mustard grows best in shady, cultivated sites, but it can become a problem in any woodland area. Garlic mustard germinates in spring and forms a rosette of leaves that survives the winter. The plant flowers the following spring, with clusters of four-petal white flowers in midspring to early summer. Leaves on flowering stalks are heart-shape and toothed. Crushed leaves smell like garlic. Cut off flowering stalks before they go to seed to prevent the plant from spreading seed and to break its biennial life cycle. Remove the cut stems from the site, because cut stalks sometimes mature their developing seeds. After several years of cutting, you should have your patch of garlic mustard under control. Of course, you'll need the cooperation of neighbors, too, if garlic mustard is growing on their properties. You can also spray garlic mustard with a nonselective herbicide, such as glyphosate (Roundup). Spray in late fall or early spring when other woodland plants are dormant but garlic mustard is actively growing.