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Garlic Mustard (Alliaria petiolata)
DNR has granted a yard waste landfilling exemption for invasive plants. Put the plants in clear plastic bags and label "Invasive Plants - Approved by WI DNR for landfilling". Read More.... DescriptionGarlic mustard is a cool-season biennial herb that ranges from 12 to 48 inches in height as an adult flowering plant. Leaves and stems emit the distinctive odor of onion or garlic when crushed (particularly in spring and early summer), and help distinguish the plant from all other woodland mustard plants. First year plants consist of a cluster of 3 or 4 round, scallop edged leaves rising 2 to 4 inches in a rosette. Second-year plants generally produce one or two flowering stems with numerous white flowers that have four separate petals. Garlic mustard is the only plant of this height in our woods with white flowers in May. Fruits are slender capsules 1 to 2.5 inches long that produce a single row of oblong black seeds with ridged seed coats. Stem leaves are alternate and triangular in shape, have large teeth, and can be 2 to 3 inches across in fruiting plants. Petioles are longer on the leaves towards the base. Garlic mustard can also be distinguished by its uproot, which is slender, white, and "s"-shaped at the top of the root. Distribution and HabitatGarlic mustard is an exotic species introduced from Europe presumably by early settlers for its supposed medicinal properties and for use in cooking. It is widely distributed throughout the northeastern and Midwestern U.S. from Canada to South Carolina and west to Kansas, North Dakota, and as far as Colorado and Utah. In Wisconsin, the plant is currently concentrated in the southeastern and northeastern counties, although distribution records indicate its presence is nearly statewide Garlic mustard grows in upland and floodplain forests, savannas, yards, and along roadsides, occasionally in full sun. It is shade-tolerant, and generally requires some shade; it is not commonly found in sunny habitats. It cannot tolerate acidic soils. The invasion of forests usually begins along the wood's edge, and progresses via streams, campgrounds, and trails.
Life History and Effects of InvasionThis species is a biennial that produces hundreds of seeds per plant. The seeds are believed to be dispersed on the fur of large animals such as deer, horses, and squirrels, by flowing water and by human activities. In our areas, seeds lie dormant for 20 months prior to germination, and may remain viable for five years. Seeds germinate in early April. First-year plants appear as basal rosettes in the summer season. First-year plants remain green through the following winter, making it possible to check for the presence of this plant in your woods throughout the year. Garlic mustard begins vegetative growth early in the spring, and blooms in southern Wisconsin from May through early June. Fruits begin to ripen in mid-July, and are disseminated through August. Viable seeds are produced within days of initial flowering. Garlic Mustard is a rapidly spreading woodland weed that is displacing native woodland wildflowers in Wisconsin. It dominates the forest floor and can displace most native herbaceous species within ten years. This plant is a major threat to the survival of Wisconsin's woodland herbaceous flora and the wildlife that depend on it. There are two modes of spread: an advancing front, and satellite population expansion possibly facilitated by small animals. Unlike other plants that invade disturbed habitats, garlic mustard readily spreads into high quality forests.
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