Garlic Mustard

Common Name: Garlic Mustard

Specific Name: Alliaria petiolata

Known Occurrence at Taylor Point:

Map areas: Bridge 4A, Bridge 4B

Category: Invasive, Non-Native, Herbaceous plant

Ecological Considerations:

Garlic Mustard is a cool season biennial herb that grows a deep, thin, white taproot that smells like horseradish. It has stalked, coarsely toothed leaves that give off an odor of garlic when crushed. In their first year, plants appear as a rosette of green leaves close to the ground. The rosettes remain green through the winter and develop into mature flowering plants the following spring. Flowering garlic mustard plants can grow from 2 to 31⁄2 feet high. They produce clusters of small white flowers, each with four petals.

Garlic Mustard rosettes are one of the first plants to turn green in spring. In May, Garlic Mustard produces seeds in erect slender pods. The seeds become black and shiny when they mature. By late June, when the garlic mustard plants have died back, they are still recognizable by the erect stalks of dry, pale brown seedpods that remain. These seed pods may hold viable seed through the summer.

Garlic mustard grows well in moist, shaded areas of river floodplains, forests, roadsides, and on the edges of woods and trails. Disturbed areas are particularly susceptible to rapid invasion by Garlic Mustard. Though invasive under a wide range of light and soil conditions, Garlic Mustard is associated with calcareous soils and does not tolerate highly acidic conditions.

Problems Posed by this Plant:

Alliaria petiolata spreads very rapidly and threatens native plants and animals. Many native plants that complete their life cycles in the springtime occur in the same habitat as garlic mustard. Once introduced to an area, garlic mustard can dominate the understory, outcompeting native plants by monopolizing light, moisture, nutrients, soil and space. Wildlife species that depend on early native plants for their foliage, pollen, nectar, fruits, seeds and roots, are deprived of these essential food sources when garlic mustard replaces them.

Native Species Affected by this Plant:

Factors Affording a Competitive Advantage to this Plant:

The prolific seed production and the long-term viability of Garlic Mustard seed in soil confer on it a competitive advantage, as does its ability to regenerate from root fragments.

Propagation Mechanisms and Related Issues Affecting Efforts to Remove and/or Eliminate this Plant from Taylor Point:

A single Garlic Mustard plant can produce thousands of seeds, which can disperse many yards from the parent plant. Its flowers may either self-fertilize or may be cross-pollinated by insects. It reproduces only by seed.

Documented Best Removal Practices and Options/Pros and Cons of Various Options:

Garlic Mustard seeds may remain viable in the soil for more than five years. Effective management efforts must prevent seed production until the stored seed is exhausted. Hand pulling plants may be effective in areas of light infestation, particularly where desirable native species also occur. Flowering plants can be removed by gently tugging at the base of the stem to remove the entire plant, including the s-shaped root. A digging tool may be helpful for loosening the soil around the base of the plants. To be effective, hand pulling efforts, most easily accomplished when soil is moist, must ensure that the entire root system is removed because new plants can sprout from root fragments. Pulled plants should be removed from site if at all possible, especially if flowers are present. After each work day, boots should be brushed off into a plastic bag to prevent the spread of seeds.

For larger infestations of garlic mustard, or when hand-pulling is not practical, flowering stems can be cut at ground level or within several inches of the ground, to prevent seed production. If stems are cut too high, the plant may produce additional flowers. Once seedpods are present, but before the seeds have matured or scattered, the stalks can be clipped, bagged and removed from the site to help prevent continued buildup of seed banks. This can be done throughout summer.

Case Studies of Removal Efforts, Lessons Learned and Recommendations:

TPRA has, over the past three years, endeavored to remove Garlic Mustard from Bridge Subsection 4A and the Taylor Point Cliffs Subsection 2H. The primary activity involved pulling the Garlic Mustard.

In 2015 on 1 workday, 10 volunteers worked for a total of 20 hours. Twenty-five pounds of Garlic Mustard was collected and placed in plastic bags to decompose.
In 2016 during 2 workdays, 14 volunteers worked for a total of 41 hours.
In 2017 during 3 workdays, 9 attendees worked for a total of 25 hours.

Lessons Learned: The Garlic Mustard population has reduced in size over the 3 years. It is clear that continued removal will be required, as will monitoring, and identification of any new infestations.

Additional Photos: