Alliaria petiolata (M. Bieb.) Cavara & Grande (Family: Brassicaceae)
Garlic mustard, a cool-season biennial herb, is one of the most widely recognized aggressive invasive plants. Unlike other plants that typically invade disturbed habitats, it spreads readily into high- quality forests, where it has no natural predators. Garlic mustard can produce hundreds of seeds per plant which are dispersed on the fur of larger animals, by flowing water, or on hikers’ clothes and boots. It may be present in an area for years before it appears and often seems to explode when it does. Areas of heavy infestation are thought to act as population sinks for certain rare native butterflies as the chemicals present in the plant interfere with their oviposition. Garlic mustard may be mistaken for a number of similar native wildflowers, but the distinctive odor of garlic that is emitted when it is crushed help to distinguish the plant.
Also known as: garlic root, garlicwort, hedge garlic, Jack-by-the-hedge, Jack-in-the-bush, mustard root, poor man's mustard, sauce-alone
Origin: Garlic mustard was introduced from Europe in the 1800s by early settlers, who hoped to use it in medicine and cooking. It was first noted as an escaped weed in 1868 on Long Island, New York.
First-year plants are a cluster of 3 or 4 heart-shaped leaves with scalloped edges rising a few inches in a rosette, which remains green through the following winter.
Adult flowering plants are usually 2 to 4 feet in height. Stems are erect, slightly ridged, and light green, and several may sprout from the same rootstock.
Leaves of mature plants are alternately arranged, 2 to 3 inches across, and triangular in shape with large teeth. Leaves toward the base of the plant have longer petioles.
Plants die after seed formation in midsummer, but remain standing as long slender yellow seedstalks with a characteristic crook at the base.
Second-year plants produce numerous white flowers that occur in terminal, tight clusters. Each small flower has 4 petals, as with other members of the mustard family. Flowering progresses up the plant as seedpods form below.
Fruits are slender capsules known as siliques that are 1 to 2 inches long. Each produces a single row of oblong black seeds. The siliques turn tan and papery as the plant dies, eventually exploding and releasing the seeds ballistically.
Garlic mustard roots can also help to distinguish the plant. They are slender, white, and “S”- shaped at the top.
Distribution: Garlic mustard is now widely distributed throughout the northeastern and Midwestern U.S. It is shade-tolerant and usually grows in upland or floodplain forests, savannas, yards, and along roadsides. Disturbed areas are most susceptible to rapid dominance, but it is invasive under a wide range of light and soil conditions, with the exception of acidic soil. Forest invasion usually begins along edges and progresses by means of streams, campgrounds, and trails.
Problem: Garlic mustard will dominate a forest floor and displace most native herbaceous species within 10 years. Many native spring wildflowers such as spring beauty, Dutchman’s breeches, and trillium occur in the same habitat as garlic mustard. Once it has been introduced to an area, garlic mustard will out-compete these species by aggressively monopolizing light, moisture, nutrients, soil, and space. Furthermore, garlic mustard plants produce allelopathic compounds that inhibit seed germination in other natives. Many wildlife species depend on the plants being suppressed, and we miss the once- vibrant display of spring flowers.
Control: Because garlic mustard seeds may remain viable in the soil for 5 years or more, effective control will require a long-term commitment. For this species, the goal is to prevent seed production until the stored seed is exhausted. Minor infestations can be eradicated by hand-pulling just before the onset of flowering or by cutting the stalks just as flowering begins. When pulling, the upper half of the root must be removed to stop buds at the root crown from sending up new stalks, and when cutting, the stalks must be cut as close to the soil surface as possible. In general, cutting will be less destructive to the soil and other surrounding plants. If flowering has progressed to the point that viable seed exists, the pulled or cut plants should be removed from the area.
Chemical control is also an option for garlic mustard. It may be controlled by applying a 1 to 2% a.i. solution of glyphosate or 1% a.i. solution of triclopyr to the foliage of individual plants and dense patches during the late fall or early spring. It is important to do this during the dormant season of most native plants but while garlic mustard is still green, since it will grow as long as there is no snow cover. It is essential to continue to monitor an area and remove plants for at least 5 years after initial efforts, but it will more likely be a lifetime commitment to keep your woods free of garlic mustard.
USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations