Garlic Mustard
Alliaria petiolata (Bieb.) Cavara & Grande

Miller, James H. 2003. Nonnative invasive plants of southern forests: a field guide for identification and control. Gen. Tech. Rep. SRS–62. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 93 p.

Plant. Cool-season biennial forb with a slender taproot found in small to extensive colonies. Basal rosettes of leaves in the first year remaining green during winter and producing one to several 2- to 4-foot (60- to 120-cm) tall flower stalks in the second year, and then dying after seed formation in midsummer. Dead plants remaining standing after June as long slender seedstalks with many upturned thin seed capsules and a characteristic crook at the stalk base. A faint to strong garlic odor emitted from all parts of the plant when crushed, becoming milder as fall approaches.

Stem. Erect, slightly ridged, light green, hairless above and hairy below. One to several stems from the same rootstock.

Leaves. Early basal rosette of kidney-shaped leaves and later alternate heart-shaped to triangular leaves, 1.2 to 3.6 inches (3 to 9 cm) long and 1 to 4 inches (2.5 to 10 cm) wide. Margins shallow to coarsely wavy toothed. Tips elongated on stem leaves. Petioles 0.4 to 3 inches (1 to 8 cm) long and reduced upward.

Flowers. April to May. Terminal, tight clusters of small white four-petaled flowers, each 0.2 to 0.3 inch (5 to 7 mm) long and 0.4 to 0.6 inch (10 to 14 mm) wide. Flowering progressing upward as seedpods form below.

Fruit and seeds. May to June. Four-sided, erect-to-ascending, thin pod, 1 to 5 inches (2.5 to 12 cm) long and 0.06 inch (1.5 mm) wide. Initially appearing to be stem branches that are alternately whorled along the stalk. Green ripening to tan and papery, exploding to expel tiny black seeds arranged in rows.

Ecology. Occurs in small to extensive colonies on floodplains, under forest canopies, and at forest margins and openings. Shade tolerant. Capable of ballistic seed dispersal of up to 10 feet (3 m). Spreads by human-, animal-, and water-dispersed seeds, which lie dormant for 2 to 6 years before germinating in spring. Experiences year to year variations in population densities. Allelopathic, emitting chemicals to kill surrounding plants and microbes.

History and use. Introduced from Europe in the 1800s and first sighted as an escaped weed in 1868 on Long Island, NY. Originally cultivated for medicinal use, but no known value now.

Recommended control procedures:

• To control two generations, thoroughly wet all leaves with a glyphosate herbicide as a 2-percent solution in water (8 ounces per 3-gallon mix) during flowering (April through June). Include a surfactant unless plants are near surface waters.
• In locations where herbicides cannot be used, pull plants before seed formation. Repeated annual prescribed burns in fall or early spring will control this plant, while “flaming” individual plants with propane torches has also shown preliminary success.

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