By Elaine Mills, Extension Master Gardener
One of the most troublesome invasive plants in Arlington County, Alliaria petiolata (garlic mustard) is an herb of European and Asian origin that was likely introduced by settlers for food or medicinal purposes. This biennial grows as a basal rosette of kidney-shaped leaves during its first year. The following spring, it develops triangular, sharply-toothed leaves with a garlic odor and sends up a 3-foot flower stalk. As it spreads and outcompetes early-blooming native wildflowers, such as spring beauty, wild ginger, and bloodroot, it deprives wildlife of the pollen, nectar, fruits, and seeds they use as essential food sources.
The leaves of garlic mustard contain compounds that are lethal to the caterpillars of native butterflies like the West Virginia white, mustard white and falcate orange-tip. This occurs when adult butterflies mistakenly lay their eggs on this plant rather than on toothworts, the mustard family plants that serve as the usual native host plants.
Garlic mustard also has allelopathic properties, meaning it releases compounds that can inhibit the growth of other plants, such as chestnut oak along with their associated mycorrhizal fungi. The composition of a forest and its regeneration may be harmed when seedlings are not able to overcome the chemical barrier and develop the normal beneficial relationship with these soil microorganisms. Garlic mustard can also modify habitat quality for salamanders and molluscs through changes in forest litter depth and composition.
Populations of garlic mustard can spread rapidly, allowing it to become the dominant plant in the undergrowth of forests. A single plant can self-fertilize and produce thousands of seeds that germinate readily in both well-lit and shaded environments and remain viable in soil for up to 10 years. Rosettes stay green over the winter, and spring growth starts very early. Density in the spring averages 25 to 70 plants per square yard but can reach much higher numbers. Birds and rodents disperse the seed, and white-tailed deer may help the plant expand its range by removing more palatable native plants from the forest understory.
Garlic mustard is difficult to control as new plants can sprout from root fragments and cut plants can form seed if they are left on the ground. For more information on manual, mechanical, foliar, and biological management options, refer to the Rutgers University Cooperative Extension fact sheet, “Identification, Control, and Impact of Garlic Mustard, Alliaria petiolata” at https://njaes.rutgers.edu/fs1212/.
- “Garlic Mustard.” 2002, 2013. Penn State University Extension.
- “Garlic Mustard (Alliaria petiolata).” Connecticut Invasive Plant Working Group.
University of Connecticut.
- “Garlic mustard.” University of Maryland Extension.
- “Rampant and Most-feared Invasive GARLIC MUSTARD Murders Crops, Wildflowers, and Forests, Poisons the Land, Kills Butterflies.” 2017. Blue Ridge Partnership for Regional Invasive Species Management.
- Sabin, Irene O. and Nicholas Polanin. 2013. “Identification, Control, and Impact of Garlic Mustard, Alliaria petiolata.”