Garlic Mustard (Alliaria petiolata)
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Miller, J.H., E.B, Chambliss, N.J. Loewenstein. 2010. A Field Guide for the Identification of Invasive Plants in Southern Forests. General Technical Report SRS-119. Asheville, NC. United States Department of Agriculture, Forest Service. 126 p.
Contents |
Plant
Cool-season biennial, with a slender white taproot, found in small to extensive colonies. Basal rosettes of leaves in the first year remain green during winter and produce 1 to several 2- to 6-foot (60- to 180-cm) tall flower stalks in the second year, and then die after seed formation in midsummer. Dead plants remain standing 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, hairy lower and hairless above. 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 (sporadically to July). Terminal, tight clusters of small, white 4-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, spiraled 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, at forest margins and openings, and less so under dense forest canopies. Shade tolerant while favoring forest edges. Litter disturbance not necessary for establishment. 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 that kill surrounding plants and microbes.
Resembles
Resembles violet (Viola spp.) in the rosette stage without stalks; and white avens (Geum canadense Jacq.) and bittercress (Cardamine spp.) that have similar small white flowers, but dissected leaves. None emit garlic odor like garlic mustard.
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.
Distribution
Found throughout the region except LA, TX, OK, and FL.
Management strategies
- Bag and dispose of plants and seed pods in a dumpster or burn.
- Treat when new plants are young to prevent seed formation.
- Pull, cut, and treat when seed pods are not present.
- Repeat cutting and mowing to prevent seeding.
- Minimize disturbance within miles of where this plant occurs, and anticipate wider occupation when plants are present before disturbance.
- Manually pull when soil is moist to ensure removal of all roots.
- 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.
- Clean shoes, equipment, and vehicles to prevent seed dispersal.
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) when plant is bolting (April through June) or Garlon 4 as a 1- to 2-percent solution (4 to 8 ounces per 3-gallon mix) in water (March through May). Apply glyphosate in winter anytime the ground is not frozen or snow present to provide control and safety to dormant native plants. Include a surfactant or an aquatic surfactant when plants are near surface waters. For more selective control, apply Plateau* (see label) where permitted.
* Nontarget plants may be killed or injured by root uptake.
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