Mustard, Garlic

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Pest Information
Common Name: Mustard, Garlic
Family Name: Brassicaceae (Mustard Family)
Latin Name: Alliaria petiolata (M. Bieb.) Cavara & Grande
Other Names: hedge garlic, sauce-alone, jack-by-the-hedge, poor man's mustard, jack-in-the-bush, garlic root, garlicwort, mustard root
Provincial Designation: Prohibited noxious
Life Cycle: Winter Annual, Biennial
Mode of Spread: Seed

Detailed Information
Provincial Situation: In Canada, garlic mustard occurs in B.C., Ontario, Quebec and N.B. In 2010, Alberta found isolated populations in Edmonton and St.Albert.
Description: A biennial that starts its first year with a slender taproot and a rosette of kidney-shaped, dark-green leaves that stay green through the winter. Second year plants can grow up to 1 m tall. The leaves are stalked, triangular to heart-shaped, with a coarsely toothed margin. Each small flower has four white petals arranged in a “cross” shape. The fruit is an erect, slender, four-sided pod, called a silique, green maturing pale grey-brown, containing two rows of small shiny black seeds which are released when the pod splits open.
Key Characteristics: One of first plants to be green in the spring.
White flowers with petals in cross shape.
Coarsely toothed triangular to heart-shaped leaves.
Crushed leaf sometimes smells like garlic or onion.
Root kink, sometimes described as “s” curve at top of root.
Similar Species: Viola sp. - Garlic mustard can be distinguished by its garlic odor (spring & summer), slender white taproot with a crook or "S" shape just below the base of the stem.
Dame's rocket (Hesperis matronalis) - Can be confused when the flowers are white, which happens occasionally. Flowers of dame's rocket are much larger and showier than those of garlic mustard, its leaves are lance-shaped and crushed foliage does have a garlic odor.
Wild & Dog Mustard - Mature plants are distinguished from Wild mustard  by their seedpods being more slender and having a slender beak that is never broad or flattened, and never containing an additional seed or two. In some plants of Garlic mustard the lower most 1-3 flowers or seedpods may be in the axils of small leaves, a characteristic it shares only with Dog mustard.
Where it Grows (Habitat & Ecology): Garlic mustard grows in dense stands in shaded and semi-shaded habitats. Although most commonly found in the understory of forests, populations in full sun do exist. In Ontario and Quebec it seems to be limited to areas where the number of degree-days equals or exceeds 3000. Edmonton has reported below 1500 degree days from 1971-2000 ($department/deptdocs.nsf/all/sag6441/$FILE/onl_s_8_twp_annual_normals_19712000.gif).
How it Spreads (Mode of Spread): Garlic mustard reproduces only from seed.
  European reports indicate occurrences of adventitious buds on the roots especially after damage have not been observed in Canada. Seeds have grooves on the outside of the seed which trap air and enable the seeds to float.
Seeds can be transported on the outside of animals, a process known as epizoochory.
Economic Importance (Beneficial Aspects): The greatest use of garlic mustard is as a green vegetable. Leaves have a high value of vitamin C and vitamin A. Values can exceed levels found in oranges and spinach. Garlic mustard may be substituted for garlic in cooking or as a salad green or in sandwiches.
Medicinal uses include treatment for gangrene, ulcers and dropsy.
Dense colonies undoubtedly help to prevent erosion.
Toxicity and Other Concerns: Garlic mustard, an early spring competitor, invades forest communities where it monopolizes light, moisture and soil nutrients, resulting in aggressive domination of the ground layer. It is a severe threat to many natural areas where it occurs because of its ability exclude many native herbaceous species.
Origin: Introduced from Europe most likely by early colonists who valued it as a medicinal and salad plant. First record in Canada, in Ontario, is from 1879. British Columbia recorded its presence in 1948.
Seed Production: Seeds can remain viable in the soil for up to 5 years. Each plant will produce between 150 and 850 seeds per plant.
Garlic mustard might be occasionally cross pollinated but most likely is self compatible in pollination. Number of seeds per siliques ranges from 6-22, average is 16. Average seed production per square meter in a dense stand under a wet deciduous woodland can be 103 600 seeds. Tough impermeable seed coat is responsible for strong dormancy. Seeds do not usually germinate until at least after a year and a half of shed. In efforts to break dormancy, 70 treatments were explored and only aggressive treatments that involved scarification and gibberellic acid were effective. It is believed that only 5-9% of seeds produce rosettes and only 2-4% will survive to flower. Seed germination is concentrated in the month of April.
Prevention: The first step is to prevent garlic mustard. Watch for your first plant and remove it  immediately. Scout field edges often, and pull or hoe out invaders. Once garlic mustard is established, prevent seed shed for several years until all viable seed is exhausted. Do not compost this plant. Seeds can remain dormant in the compost and re-germinate.
Cultural Control: Because Garlic Mustard seeds can remain in the soil for 5 or more years, the same site will need to be monitored for some time until the seed bank is depleted. This species also undergoes
considerable fluctuations in density, leading to assumptions that it has been controlled when in fact, it is still very much present. Hand pulling works best for small infestations. Be sure to pull the entire root as new plants can grow from root fragments left in the soil. Roots pull out easier in damp soil than in dry. It is best to remove and bag pulled plants, particularly if they are
flowering, because viable seeds will form even in cut or pulled flowers.
Competition: Garlic mustard is encouraged to spread when natural vegetation is disturbed. Reports have included garlic mustard as allelopathic, inhibiting other plants from germinating. It produces a toxin which inhibits mycorrhizal fungi which interferes with the growth of other plants and trees
Fertility: Large dense populations are often associated with well-fertilized sites and several collections have been made on garbage dumps. Garlic mustard is described as a nitrophile, a plant that prefers to grow on soil with higher nitrogen content.
Cultivation: Seedlings can be killed easily by cultivating the soil after germination.
Mowing: Mowing plants will encourage new flowering shoots from the root crown with the ability to produce viable seeds. If stems are cut too high, the plant may produce additional flowers at leaf axils. Once seedpods are present, but before the seeds have matured or scattered, the stalks can be clipped, bagged and removed from the site to help prevent continued buildup of seed stores. This can be done through much of the summer.  Later in the growing season, plants are less likely to re-grow after being mown.
Grazing: Unpalatable to grazers and disturbance from trampling would increase an infestation. White-tailed deer prefer native plants to garlic mustard, large deer populations may help to expand it by removing competing native plants and exposing the soil and seedbed through trampling.
Fire: Fire has been used to control garlic mustard in some large natural settings but, because burning opens the understory, it can encourage germination of stored seeds and promote growth of emerging garlic mustard seedlings. For this reason, burns must be conducted for three to five consecutive years.
Bio-Control: Over 30 different insects are known to attack garlic mustard in its native range, non e of these enemies occur in North America. A search for suitable biological control agents for garlic mustard was initiated in 1998 by MSU collaborators at Cornell University, the University of
Minnesota, and CABI Bioscience in Switzerland. Efforts are now focused on four beetles (weevils) in the genus Ceutorhynchus, whose larvae target multiple stages in garlic mustard’s life cycle.
Other Canadian Links:
Herbarium Collections: None found
Life Cycle: Biennial or winter annual. Winter survival is done through seed or in the form of rosettes. It is believed that glucosinolates and related compounds enable garlic mustard to grow vigorously at near freezing temperatures in late autumn and early spring. In Ontario, seedlings will present in late March, April, May to early June depending on conditions and second year plants had flowers open as early as mid April.

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Last Modified: January 06, 2012

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