Garlic mustard as an invasive species

[1] It is listed as a noxious or restricted plant in the following states: Alabama, Connecticut, Massachusetts, Minnesota, New Hampshire, Oregon, Vermont, and Washington.

[1] The most promising biological control agent, the monophagous weevil Ceutorhynchus scrobicollis, specifically studied since 2002, has been blocked for introduction into the US repeatedly by the USDA Technical Advisory, TAG, group before being approved in 2017, though regulatory hurdles remain.

In many areas of its introduction in Eastern North America, it has become the dominant under-story species in woodland and flood plain environments, where eradication is difficult.

[16] Garlic mustard produces a variety of secondary compounds including flavonoids, defense proteins, glycosides, and glucosinolates that reduce its palatability to herbivores.

Non-chemical non-biological control methods include removal by hand-pulling or cutting at the base, mowing, burning, or manipulation of the environment to reduce light.

[22] Chemical control may be achieved to some extent by foliar application with a number of herbicides, although their use is much more efficacious in highly disturbed situations, like agricultural monocultures or urban and suburban gardens, than in complex settings, like forests and well-established meadows or prairies.

[23] However, there are native and desirable plants that are active even before garlic mustard is, and/or at the same time in early spring, such as flowers from the genera Pulsatilla and Helleborus of the family Ranunculaceae.

[23] Chemical control methods that involve heavy equipment or human trampling can compact soils, affecting all plants negatively.

All non-biological methods of control must be repeated for 2–5 years to be effective—as most infestations occur in sites where a considerable seed bank has been established.

Surviving roots regrow and produce new seed pods, enabling the infestation to potentially be quickly reestablished.

Continual reintroduction of garlic mustard to areas where it has been eradicated is also highly likely until an effective biological control situation is established, as the long-lived seeds are produced in great quantities and are readily distributed by animals and human activity.

For more complex ecosystems such as forests, trampling and other physical disturbance such as soil compaction, the spreading of seeds from clothing, chemical toxicity, unwanted non-targeted species damage, demanding human labor, petrochemical consumption, and other factors are eliminated or greatly reduced with effective biological control.

[31] Despite the demonstrated effectiveness of C. scrobicollis and, potentially, C. constrictus, the importation and release of biological control agents such as those may be stymied by heavy research and regulation requirements.

[24] Of the 76 natural enemies garlic mustard has in its native range, several have been tested for use as potential biological control agents.