Garlic Mustard (Alliaria petiolata)
Key Identification Features
Heart-shaped leaves with strongly toothed edges
Clusters of white flowers with four petals
Strong garlic smell when crushed
Description
Garlic mustard has a biennial life-cycle and takes two years to mature and produce seeds. Basal leaves of an immature, first year plant are dark-green and kidney shaped with scalloped edges and are ~6 to 10 cm in diameter.
In its second year, the alternating stem leaves become more triangular shaped, 1 to 5 cm long, and have sharper teeth, with leaves becoming gradually smaller towards the top of the hairy stalk.
Garlic mustard flowers arrive in early April and die by June. Flowers have 4 small white, 3-6mm petals arranged symmetrically. Individual flowers contains six stamens, two shorter and four longer. Mature flowering plants reach 3.5 feet tall, although shorter flowering specimens may be found.
Garlic mustard has a distinctive garlic smell when crushed though older plants may not have as strong a scent.
Native Range
Garlic mustard is native to Europe and Asia and was originally introduced as a medicinal and herbal plant by European settlers. It has since spread throughout much of the Northeast and Midwest.
Habitat and Dispersion
Garlic mustard is commonly seen growing along forested roadsides and forest floors and thrives in wooded areas. It tolerates deep shade and is able to invade understory areas due to it’s germination before leaf-out. It forms dense stands in the understory habitat and crowds out native herbaceous understory plants such as trillium and trout lily. Garlic mustard is allelopathic and inhibits the growth of other plants. It is also thought to decrease species richness in the understory, though more research is needed to understand how severe the impact is.
Garlic mustard can produce an average of 600 seeds per plant before dying in June. The seeds generally germinate within one to two years, but may remain viable for up to five years in the seed bank. Seed dispersal is mainly by humans or wildlife carrying the seeds.
Best Management Practices
The best method for controlling garlic mustard, or any other invasive plant, is to prevent its establishment. Disturbances in the forest understory that would allow for rapid invasion should be minimized. This would include limiting foot traffic, grazing, and erosion-causing activities. Monitoring the forest understory and removing any garlic mustard plants as soon as they are introduced will help to prevent the establishment and spread of this invader.
Hand pulling works well on smaller patches and helps to prevent further spread. When pulling by hand, remove at least the upper half of the root to prevent a new stalk from forming. Hand pulling is easily done in the spring when the soil is soft or after rains. Hand-pulling should be done before seeds are formed and needs to be continued for up to five years in order to deplete any established seed bank.
On larger patches too big to remove by hand, chemical applications can be effective. Glyphosate-based herbicide can be an effective method for removal, however, Glyphosate herbicides are non-selective, so caution must be used when non-target species are in the area. Chemical applications are most affective during the spring (March-April) when garlic mustard is one of the few plants actively growing. As always, check with local regulatory agencies to determine the regulations involved with chemical treatments.