Invasive Garlic Mustard

Year 1 Plants

Seeds require a cold dormant period, or stratification, of at least 8 months. Most seeds germinate in spring, as early as February, with some continuing through fall. Seeds can survive in the soil up to 10 years.

Plants grow into multi-stalked clusters of low-growing basal rosettes. Leaves are kidney-shaped with rounded scalloped edges that smell like garlic when crushed. The plant will overwinter as a basal rosette. First-year plants can easily be overlooked at low levels.

Year 2 Plants

In the early spring, basal rosettes will have a surge of growth as they bolt and bloom. The flowering stalk is 1- to 4-feet tall with triangular, toothed-edged leaves. Its flowers have four white petals. Seeds form in upright seed pods known as siliques.

As plants die, they dry and release an average of 360 black seeds in early summer. Large plants can produce more than 8,000 seeds. Clusters of dead dry stalks will likely have first-year germinates nearby.

Management of Garlic Mustard

Removing garlic mustard is a multi-year process that focuses on preventing at least 90% of plants from producing seeds to prevent spread. Be prepared to manage annually for at least five years to deplete the seed bank and plan for long-term monitoring to prevent reinvasions. Sporadic management can make infestations worse.

No management method is entirely effective. Before treatment, develop a long-term strategy that considers available time and labor resources, as well as the infestation size and location.

Land managers face competing obligations; prioritizing sites for management is important for success. For help prioritizing sites, explore a management decision tree in the Midwest Invasive Plant Network’s Garlic Mustard Guide.

• Monitor for new or growing populations along pathways of spread and focus on treating manageable garlic mustard populations.
• Top priority sites are new invasions, satellite populations, plants near trails and streams, and the leading edge of infestations.

In Illinois, there is a 6- to 8-week window in the spring to control second-year plants before they produce seed. Do not attempt removal if plants are dry and seeds are falling out; this will further its spread.

Add a reminder to your calendar

Monitor in the fall   Monitor and control in spring

Prevention of Garlic Mustard

• Keep garlic mustard out of your forest: If visiting other properties, stay on established roads and trails and clean boots, tires, and horse hooves before returning to your property.
• Work with neighboring property owners: Discuss concerns about invasives with neighboring property owners and plan to work together to manage them.

Mowing/Cutting

This method works for large populations of bolting plants. Cut stalks at ground level to eliminate seed production. Stalks with siliques can still form viable seed. 

Prescribed fire

In forest communities adapted to fire, a prescribed burn can help control large infestations and stimulate native plant growth. Always follow state and local regulations and safety protocols. Managers need an approved plan and a permit from the Illinois EPA. Explore an Introduction to Prescribed Fire and more resources for implementing a prescribed fire.

A mid-intensity burn in the spring is most effective. A handheld propane torch can also be used for spot treatments. Fire will remove leaf litter and prompt seeds to germinate. You can treat the new seedlings with herbicide to deplete the seed bank faster.

• Early spring burns target basal rosettes and bolting plants but can harm early wildflowers.
• Late spring burns target new seedlings and basal rosettes but can damage actively growing plants.
• Fall burns can reduce basal rosettes. 

Chemical control

Herbicide can be a low-cost, low-labor option for large infestations. Always read and follow product labels before use. Avoid impacting desirable plants with herbicide overspray. Apply enough herbicide to wet foliage, but not so much that it drips off.

Anyone who applies pesticide on public lands must be licensed. Learn more from the Pesticide Safety Education Program.

Use products with Glyphosate or Triclopyr to treat basal rosettes and bolting plants. Apply in early spring or fall. Late applications, during or after flowering, can reduce viable seed production but are not entirely effective.

Concentrations

• Glyphosate, 1% to 3% v/v diluted in water.
• Triclopyr, 1.5% v/v diluted in water.

Deer exclusion

White-tailed deer move seed and avoid eating garlic mustard, so infestations can increase herbivory pressure on native plants. This can reduce native plant abundance and allow garlic mustard to increase in dominance. Exclude or manage large deer populations when removing garlic mustard.

Biological control  

Researchers continue to explore if European aphids that feed on garlic mustard can be used for control.

No management

Long-term monitoring has provided some evidence that long-standing garlic mustard populations, at least 50 years old, may be self limiting and could decline without management. These findings are not well supported.

Research Updates

Midwestern researchers recently explored the time frame needed to apply herbicides in order to prevent seed production.

Results: Applying Glyphosate and Triclopyr during the flowering stage reduces viable seed production. This was not 100% effective, so do not use this as a primary method to control garlic mustard. This gives land managers an extra 2 to 3 weeks to apply herbicide to garlic mustard in the spring.

References

• Residence time determines invasiveness and performance of garlic mustard in North America
• Garlic Mustard in the Midwest: an Overview for Managers
• Complex population dynamics and control of the invasive biennial Alliaria petiolata.
• Do applications of systemic herbicides when green fruit are present prevent seed production or viability of garlic mustard?