Garlic Mustard: A Threat to Woodlands

Have you seen this white flowering plant and wondered what it could be? Have you noticed it growing more often along roadsides or in disturbed areas? This species is called Garlic Mustard (Alliaria petiolata) and was brought from Europe in the 1800s as an edible and medicinal plant. As with any invasive, Garlic Mustard does not currently have any natural predators. These could include small mammals or insects that feed on the vegetation, birds that could feed on the seeds, or diseases that keep the population in check. There are several characteristics specific to Garlic Mustard that make it a prolific invasive species:

Garlic Mustard can produce up to 7,900 seeds per plant but usually averages around 600 seeds
Seeds can last in the soil for many years before germinating, sometimes up to 10
Forms dense stands
Self pollinates if needed
Highly shade tolerant
Garlic Mustard also produces allelopathic compounds that are released in the soil to prevent germination of native plants and fungal associations

Garlic Mustard can be found growing in most habitats but is common in disturbed areas, edge habitats, roadsides, streams, and woodlands. It is easily identifiable by the garlic smell that is produced when the leaves are crushed. The leaves have a heart shaped appearance that could be confused with violets when they first emerge. Another aspect of Garlic Mustard that makes it a successful invader is that fact that it develops over two years. In the first year, the plant forms basal rosettes of leaves that obtain nutrients and prepare for the second year. It dies back in the winter but during the second year, the plant can get up to 3 feet tall and forms flowers on multiple branches. The flowers have four white petals and are relatively small. Plants flower in early spring to mid-summer and seeds develop in late July and August.

An unfortunate side effect of the introduction of Garlic Mustard is its impact on the West Virginia White Butterfly (Pieris virginiensis). This species is uncommon in Vermont and has been listed as a species of special concern since 1990. The West Virginia White Butterfly relies on species such as Crinkleroot (Cardamine diphylla) and Cut-leaved Toothwort (Cardamine concatenata) as a food source for caterpillars. When Garlic Mustard is present, it not only takes over the woodland habitat of native plants such as Toothwort, but also confuses the butterflies. Garlic Mustard and the Toothworts are in the same plant family and produce similar visual and chemical signals for these butterflies. However, the Garlic Mustard leaves are toxic to West Virginia White Butterfly caterpillars and will kill them after it has been consumed.

What can we do? Garlic Mustard is easy to hand pull in either the first year or second year stage. It is important to pull second year plants before seeds have developed or matured to prevent future spread. Being aware of the plant’s presence and actively managing over several years by hand pulling and preventing seed dispersal will make a big difference in the long run. Because the plant has first and second year generations, it is important to be consistent and diligent with hand pulling in order to reduce the seed bank. Be sure to get the entire tap root to prevent re-sprouting. Once pulled, Garlic Mustard plants can still release mature seeds so it is important to solarize the plants to completely kill them. Mowing or weedwacking spreads seeds and creates future infestations. It is also important to clean shoes and gloves after pulling to avoid spreading the seed. Some people even like to make hummus or pesto with the fresh leaves due to the garlic-like taste of the plant. When harvesting for consumption, be sure to assess the safety of the location and soil before eating.

Visit the Vermont Invasives Website to learn more about Garlic Mustard.

Visit the Vermont Invasives Website to learn about safe disposal of invasive plants.

Visit the Northern Woodlands Website to learn how to make Garlic Mustard Pesto.