Alliaria petiolata or Alliaire officinale
First year plants form low rosettes that remain green throughout the winter. Second year plants grow from 0.3 - 1.3 m (1-4 ft) tall. They produce attractive white flowers in early spring producing long (2.5 - 6.5 cm) narrow seed pods 4 - 8 weeks afterwards that can persist and drop seed throughout the summer. Seeds can remain viable in the soil for at least five years.
Photo: John Oyston Toronto Ravine, Dec 2010
Garlic mustard can be insect or self-pollinated. A single plant is capable of producing thousands of seeds which are easily transported by animal and human activity over large distances.
It is found predominantly in rich moist forests and along stream banks but can also tolerate full sun. It rapidly colonizes disturbed sites. Garlic mustard prefers calcareous soils and does not tolerate acid conditions.
Garlic mustard was likely imported by settlers from Europe and Asia for use as a medicinal and cooking herb. It was first recorded in 1868 in Long Island NY.
It is a biennial that can rapidly overtake native vegetation. In addition to directly competing for light, moisture and nutrients, it secretes a phytochemical that suppresses other plants, including tree seedlings. Since garlic mustard most readily colonizes disturbed areas, try to maintain a healthy native plant ecosytem.
Hoeing first year rosettes and hand pulling is most effective before populations become widespread. Garlic mustard can re-sprout from root and stem fragments. Pull when the soil is moist to aid in removing the entire root.
Second year growth can also be cut close to the ground before releasing seed. New flowers can grow from leaf axils, so care must be taken to cut below the first axil.
Remove all plant material, particularly seed pods, from the site and dispose of in tightly sealed garbage bags. To ensure that seeds are not dispersed from landfills by seagulls and other means, try to solarize or burn them before disposing of the residue. DO NOT COMPOST.
Burning and chemical intervention can in some cases be effective, but extreme care should be taken around existing native vegetation. Glyphosate-based biocides can be taken up by woody species. Since garlic mustard prefers moist areas, care should also be taken to avoid contaminating water courses.
Whichever method is used, it is essential to monitor the site annually to ensure that new seedlings are not emerging.
Biological control involving several types of European weevils (Ceutorhynchus spp) including two stem-feeders, a seed-feeder, and a root crown feeder, are under study. While these insects do help to control garlic mustard in its native Europe environs, it is essential to ensure that the weevils will feed exclusively on garlic mustard before releasing them in North America.
Garlic mustard in flower (Photo: John Oyston)