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Garlic Mustard (Allaria petiolata)

Description: Garlic mustard is an invasive, cool season, biennial herb in the mustard family. It has triangular to heart shaped, coarsely toothed leaves that smell like garlic if crushed. In its first year, seeds germinate early in the spring and grow as a low rosette. After over wintering, the rosette sends up a 2 to 4 foot tall stalk, which produces button-like clusters of small white flowers. Each flower has four petals in the shape of a cross. Garlic mustard begins growth and flowering in early spring, and begins to set seed in May and June. This plant produces abundant seed (more than 2000 per plant) which remain viable in the soil for 4-6 years.

Distribution: Garlic mustard was introduced to North America from Europe in the early 1800’s. It was brought here most likely for medicinal uses. It has spread into many areas of Johnson County and Iowa. Garlic mustard predominantly invades woodland communities, rapidly spreading and overwhelming native woodland wildflowers and other species.

What’s The Problem?: Garlic mustard grows early in the Spring and produces a dense carpet of plants which shade out and rob nutrients from native woodland wildflowers and forbs such as Dutchman’s Breeches, Spring Beauty, and Trillium. This plant can eventually become the dominant plant in woodlands. Garlic mustard reproduces monoeciously (a single isolated plant can produce numerous seeds), has a large tolerance to cold weather, and its seed dormancy varies which allows it to avoid germination in unfavorable conditions. Garlic mustard also produces chemicals and odors which herbivores find disagreeable. Garlic mustard grows where access with typical management equipment is difficult.

Management Methods: Current control methods for garlic mustard are mechanical cutting, hand pulling, prescribed fire, and application of burndown/systemic herbicides. Because seed remains viable in the soil for 4-6 years, control of garlic mustard requires a long-term commitment. Minor or initial infestations can be hand pulled. Be sure to pull the entire plant and root system, as new sprout can occur from small root fragments. Plants will pull easiest if they are small and the soil is moist. Cutting of the flower stalk soon after flowering will eliminate seed production, and if cut at the ground, plants will not resprout. This must be carried out until the seed bank is exhausted, which may take several years. If seedpods have formed before cutting, plants should be bagged up and removed to prevent buildup of seed stores. For very heavy infestations, applications of systemic herbicides are also effective. Apply only to foliage or rosettes of garlic mustard, as damage to non-target plants can occur if contacted with herbicide. Be certain to correctly identify plants and use the proper chemicals at labeled rates. Be sure to read and fully understand chemical labels before usage. Prescribed burning can be an effective tool to combat garlic mustard, if used correctly and consistently. Fire can open up the understory of a forest and encourage germination of garlic mustard, therefore, annual burnings for up to 5 years may need to be done to sufficiently kill existing plants and exhaust seed stores. Burning may need to be supplemented with other control methods, such as hand pulling. Biological control research is being done around the nation to investigate other management methods for control of garlic mustard. None are currently approved for control.