Bill Johnson

Garlic Mustard

Alliaria petiolata (Bieb.) Cavara & Grande
Mustard family (Brassicaceae)

Origin: Europe

Background
Garlic mustard was first recorded in the United States around 1868, from Long Island, New York, and was likely introduced by settlers for food and medicinal purposes.

Distribution and Habitat
Garlic mustard has been reported to be invasive in natural areas throughout the northeastern U.S. and in scattered localities in the Midwest, Southeast, western states, and Alaska. It occurs in moist to dry forest habitats, forest edges, floodplains, and along roadsides and disturbed lands and is not tolerant of highly acidic soils. White-tailed deer assist in its spread by eating native plant species that they prefer and are adapted to eat, leaving the garlic mustard behind.

Ecological Threat
Garlic mustard has displaced vast areas occupied by native spring wildflowers like spring beauty (Claytonia virginica), wild ginger (Asarum canadense), bloodroot (Sanguinaria canadensis), trilliums (Trillium species) and toothworts (Cardamine). Three native butterfly species, the West Virginia white (Pieris virginiensis), mustard white butterfly (Pieris oleracea), and the falcate orange-tip (Anthocharis midea annicka), are especially impacted when garlic mustard displaces toothworts, its host plants. Chemicals in garlic mustard are toxic to the larvae of the native butterflies. Other chemicals have been found to affect mychorrhizal fungi associated with native trees, resulting in suppression of native tree seedling growth.

Description and Biology

• Plant: biennial herb in the mustard family (Brassicaceae); first-year plants are low rosettes of kidney shaped leaves; second-year plants produce single or multiple flowering stalks 1-4 ft. high and, then die back by late spring; dried fruiting stalks may persist for many months.
• Leaves: crushed leaves and stems smell like garlic; first-year leaves are kidney-shaped with scalloped margins; leaves of mature, second year plants are heart-shaped with toothed margins and pointed tips.
• Flowers, fruits and seeds: flowers occur in small button-shaped clusters, flowers have four petals in the shape of a cross; fruits are slender, erect capsules (siliques); seeds are 2½-3 mm long, slender and tan to dark.
• Spreads: a single plant can produce hundreds of seeds, most of which fall nearby but may be carried further by wind, water, wildlife and people.
• Look-alikes: toothworts (Cardamine or Dentaria), sweet cicely (Osmorhiza claytonii), wild anise (Osmorhiza longistylis) and early saxifrage (Saxifraga virginiensis).

Chris Evans, River to River CWMA

Robert Vidéki, Doronicum Kft.

Prevention and Control
Garlic mustard seeds can survive for five or more years in the soil. Effective management requires a long-term effort. Hand removal of plants along with the roots, is effective for light, scattered infestations. Flowering plants can be cut low to the ground in spring to prevent seed production but cut plants can resprout. Careful hand removal and bagging of plants with mature fruits can be done as soon as fruits are present. Systemic herbicides containing glyphosate are effective but repeated treatments are usually needed because of the large seed stores in the soil (see Control Options). Researchers are investigating potential biological control agents but none are available at this time.