Biological control of garlic mustard in Minnesota

Background

Garlic mustard (Alliaria petiolata) is an environmental weed in Minnesota that is of Eurasian origin and invades native forest habitats. It is one of the most notorious invasive weeds in Minnesota, and has the capability to displace various native plant species, including spring ephemerals, annual and perennial herbaceous species, and seedlings of canopy trees. 

The prospect of using Eurasian insects to control garlic mustard has been investigated over the past 25 years, and two highly specialized species of beetles have now been identified as very promising biological control agents: Ceutorhynchus scrobicollis and C. constrictus. Both of these species have undergone many years of safety testing under quarantine conditions, and the results indicate that the risk that the release of these beetles would pose to any native or commercially important species throughout North America is minimal at most. Detailed analyses additionally suggest that the establishment of one or both of these beetles could greatly reduce the abundance of garlic mustard in Minnesota, reducing existing pressure on native plant species. 

Based on these considerations, the United States Department of Agriculture has approved the release of one of the species (C. scrobicollis). Research on the other beetle species began later, but that species has also passed the first regulatory hurdle based on an indication of vanishingly low risks to native and commercial species. 

In this project, researchers will conduct the first releases of approved species of these garlic mustard beetles in Minnesota, and analyze the benefits that they provide to native plant diversity in the state.

Research questions

• What is the risk/benefit for the release of the two weevil species in Minnesota?
• What is the status of garlic mustard and other native plant populations before and after release?

Practical implications

This research provides a context within which to take advantage of over 25 years of research on the potential to achieve biological control of garlic mustard in the United States. The release of biological control agents against this environmental weed is the best way to protect native plants—including spring ephemeral forbs and tree seedlings—from direct and indirect negative effects of this weed. It is also the best way to reduce the need for time-consuming and expensive control methods such as hand-pulling, prescribed burning, mowing, and herbicide use.

Findings

This project began in July 2026 and is in progress for the next several years. Please check back at a later time for updates.

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