Garden Update
Week of September 16, 2022
Kathleen Cue, Nebraska Extension Horticulture Educator in Dodge County
Garlic Mustard
When it comes to invasive weeds, garlic mustard ranks high in its scary potential to rapidly change an ecosystem. A natural understory plant, garlic mustard readily colonizes wooded areas, outcompeting native vegetation to the point of massive understory loss. A change in food sources means wildlife, including song birds and insects, must move to new locations for forage. Just how rapid this change happens is truly alarming. A site visit I made to a local campground four years ago now has a wooded understory completely covered in garlic mustard. The area is now eerily silent, bereft of sounds of birds and other wildlife.
In addition to changing a wooded area’s understory, garlic mustard negatively impacts trees. The Wisconsin Department of Natural Resources has found that plants exude an anti-fungal chemical into the soil. This kills mycorrhizal fungi, the beneficial association between fungus and tree roots that gives trees greater resiliency for water and nutrient uptake.
Garlic mustard, Alliaria petiolata, is a member of the cabbage family. It was brought to this continent by settlers, purportedly for garlic mustard’s culinary and medicinal uses. The leaves, when crushed, give off a garlic odor. Garlic mustard was first documented in the state of New York in 1868 and has since spread across the continent. Most sources list garlic mustard as a colonizer of disturbed sites but unfortunately I’ve found it growing in sites that have had little disturbance. Each plant can release a thousand seeds, which spread by wind, water, and soil movement. Garlic mustard is introduced into new areas by the feet of people, pets, and wildlife.
Garlic mustard is a biennial, spending its first growing season as a basal rosette of leaves. Leaves are kidney-shaped with large irregular serrations on leaf edges. The plant’s second year of growth is the bolt year, where plants develop 2 to 3-foot tall flowering stalks made up of white 4-petaled flowers. In this second year, the leaves are heart-shaped with irregular serrations.
We can take advantage of garlic mustard’s non seeding first year of growth as the ideal time to manage it. If infestations are small, hand-pulling is effective. For a selective herbicide option, a tank mix of 2,4-D and triclopyr is effective and can be applied in the first year of basal growth or in the second year prior to flower development.
Stands of garlic mustard that have been in place for years have developed an extensive seed bank that makes this invasive extremely difficult to manage. Research by Michigan State University indicate eradication of garlic mustard requires a 10-year commitment to treating, pulling, and monitoring.
Photo: Garlic Mustard
Learn more at horticulture at Trees, Plants and Insects, Kathleen Cue's Horticulture page.