Garlic Mustard can outcompete native herbaceous species, depriving them of light, moisture and space. It also negatively impacts mycorrhizal fungi that are important underground symbionts for northern hardwood species, allowing it to compete with these woody species. In some states this plant threatens native butterfly species by outcompeting their native host plants. When the butterflies lay their eggs on Alliaria petiolata the larvae do not seem to survive as well. The seeds of Alliaria petiolata usually fall just beneath the plant, but it is probably dispersed longer distances by people when seeds get attached to boots and clothing.

Garlic Mustard is successful in many types of habitats. It prefers moist, shaded areas, but can grow well at roadsides, edges of woods, along trails and in forest openings. Because of its shade tolerance it is one of few invasives that can be present and dominate a forest understory. A single plant can produce thousands of seeds, which scatter as much as several meters from the parent plant.

Control Methods

Hand Pulling
Hand pulling is an effective method for removing small populations of garlic mustard, since plants pull up easily in most forested habitats. Plants can be pulled during most of the year. However, if plants have capsules present, they should be bagged and disposed of to prevent seed dispersal. Care should be taken to minimize soil disturbance but to remove all root tissues. Soil disturbance can bring garlic mustard seeds to the surface, thus creating a favorable environment for their germination. To avoid this, soil should be tamped down firmly after re- moving the plant. Re-sprouting is uncommon but may occur from mature plants not entirely removed.

Cutting
Cutting is effective for medium- to large-sized populations depending on available time and labor resources. Cut stems when in flower (late spring/early summer) at ground level either manually (with clippers or a scythe) or with a motorized string trimmer. This technique will result in almost total mortality of existing plants and will minimize re-sprouting. Dormant seeds in the soil are unaffected by this technique due to minimal disturbance of the soil. However, as viable seeds may be produced from cut stems, they should be removed from the site when possible. Cuttings should be conducted annually until the seedbank is depleted.

Key Identifiers

Garlic Mustard is an herbaceous biennial whose flowering form can reach 1 m (3.3 ft.) in height. The first year plants are a basal rosette of leaves that remain green throughout the winter. They develop into mature flowering plants the following spring. The lower, dark green leaves are reniform (kidney-shaped), while the stem leaves are alternate and deltoid. The basal leaf blades can be 6-10 cm (2.4-4 in.) long and wide, while the stem leaves are 3-8 cm (1.2-3.1 in.) long and wide, gradually decreasing in size as they go up the stem. The margins of the leaves are coarsely toothed. The leaves give off a strong garlic odor when crushed. The flowers of Alliaria petiolata are consistent with those of the mustard family. That is, there are four white petals arranged in a cross shape, and these are 5-6 mm (0.25 in.) in diameter. The flowers are arranged in terminal racemes. They appear in the early spring (April-May), and fruits are produced by May. The cylindrical, shiny, black seeds are 3 mm (0.1 in.) in size and are contained in pods called siliques. These siliques are 2.5-6 cm (1-2.4 in.) long and 2 mm (0.08 in.) wide and contain 10-20 seeds.