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Garlic Mustard

Alliaria petiolata

As an invasive species 5

Garlic mustard was introduced in North America as a culinary herb in the 1860s and is an invasive species in much of North America. As of 2006 and occurs in 27 midwestern and northeastern states in the US, and in Canada. Like most invasive plants, once it has an introduction into a new location, it persists and spreads into undisturbed plant communities. 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.

The insects and fungi that feed on it in its native habitat are not present in North America, increasing its seed productivity and allowing it to out-compete native plants.

Garlic mustard produces allelochemicals, mainly in the form of the compounds allyl isothiocyanate and benzyl isothiocyanate, which suppress mycorrhizal fungi that most plants, including native forest trees, require for optimum growth. However, allelochemicals produced by garlic mustard do not affect mycorrhizal fungi from garlic mustard's native range, indicating that this "novel weapon" in the invaded range explains garlic mustard's success in North America. Additionally, because white-tailed deer rarely feed on garlic mustard, large deer populations may help to increase its population densities by consuming competing native plants. Trampling by browsing deer encourages additional seed growth by disturbing the soil. Seeds contained in the soil can germinate up to five years after being produced (and possibly more). The persistence of the seed bank and suppression of mycorrhizal fungi both complicate restoration of invaded areas because long-term removal is required to deplete the seed bank and allow recovery of mycorrhizae.

Garlic mustard produces a variety of secondary compounds including flavonoids, defense proteins, glycosides, and glucosinolates that reduce its palatability to herbivores. Research published in 2007 shows that, in northeastern forests, garlic mustard rosettes increased the rate of native leaf litter decomposition, increasing nutrient availability and possibly creating conditions favorable to garlic mustard's own spread.

Preventing seed production and depletion of the soil seed bank are key to eradicating infestations. Non chemical control includes removal by hand-pulling or cutting at the base; mowing; burning; or manipulation of the environment to reduce light. Pulling is more effective if the root is removed. Garlic mustard may invade forested sites where the canopy has been disturbed, so management by planting or encouraging other plants to intercept light will aid control, or prevent new infestations. Control is best in early spring before flowering. Removed plants should be bagged or burned, as seeds or roots may survive composting.

Chemical control may be achieved by foliar application with a number of different herbicides. Timing herbicide applications to early spring or late fall may protect native or desirable plants in the same locations as garlic mustard is generally active across a longer season than other plants in northern temperate climates. All methods of weed control must be repeated for 3–4 years or longer to be effective—as seeds germinate, or as surviving roots re-sprout the infestation may be quickly re-established.

Several species from its native range are being tested for use as potential biological control agents. In particular, five weevil species from the genus Ceutorhynchus and one flea beetle were selected as candidates during preliminary testing.

As an invasive species 6

Garlic mustard was introduced in North America as a culinary herb in the 1860s and is an invasive species in much of North America. As of 2006 and occurs in 27 midwestern and northeastern states in the US, and in Canada. Like most invasive plants, once it has an introduction into a new location, it persists and spreads into undisturbed plant communities. 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.

The insects and fungi that feed on it in its native habitat are not present in North America, increasing its seed productivity and allowing it to out-compete native plants.

Garlic mustard produces allelochemicals, mainly in the form of the compounds allyl isothiocyanate and benzyl isothiocyanate, which suppress mycorrhizal fungi that most plants, including native forest trees, require for optimum growth. However, allelochemicals produced by garlic mustard do not affect mycorrhizal fungi from garlic mustard's native range, indicating that this "novel weapon" in the invaded range explains garlic mustard's success in North America. Additionally, because white-tailed deer rarely feed on garlic mustard, large deer populations may help to increase its population densities by consuming competing native plants. Trampling by browsing deer encourages additional seed growth by disturbing the soil. Seeds contained in the soil can germinate up to five years after being produced (and possibly more). The persistence of the seed bank and suppression of mycorrhizal fungi both complicate restoration of invaded areas because long-term removal is required to deplete the seed bank and allow recovery of mycorrhizae.

Garlic mustard produces a variety of secondary compounds including flavonoids, defense proteins, glycosides, and glucosinolates that reduce its palatability to herbivores. Research published in 2007 shows that, in northeastern forests, garlic mustard rosettes increased the rate of native leaf litter decomposition, increasing nutrient availability and possibly creating conditions favorable to garlic mustard's own spread.

Preventing seed production and depletion of the soil seed bank are key to eradicating infestations. Non chemical control includes removal by hand-pulling or cutting at the base; mowing; burning; or manipulation of the environment to reduce light. Pulling is more effective if the root is removed. Garlic mustard may invade forested sites where the canopy has been disturbed, so management by planting or encouraging other plants to intercept light will aid control, or prevent new infestations. Control is best in early spring before flowering. Removed plants should be bagged or burned, as seeds or roots may survive composting.

Chemical control may be achieved by foliar application with a number of different herbicides. Timing herbicide applications to early spring or late fall may protect native or desirable plants in the same locations as garlic mustard is generally active across a longer season than other plants in northern temperate climates. All methods of weed control must be repeated for 3–4 years or longer to be effective—as seeds germinate, or as surviving roots re-sprout the infestation may be quickly re-established.

Several species from its native range are being tested for use as potential biological control agents. In particular, five weevil species from the genus Ceutorhynchus and one flea beetle were selected as candidates during preliminary testing.

Similar Native Species 7

Several native white flowered plants, the toothworts (Dentaria spp.) and sweet cicely (Osmorhiza claytonii), bloom at about the same time as garlic mustard and may be mistaken for it. The leaves of native violets (Viola spp.) and the non-native creeping Charlie (Glechoma hederaea) may be mistaken for first year garlic mustard plants.

Sources and Credits

  1. (c) 57Andrew, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/29954808@N00/16647291293/
  2. (c) Donald Hobern, some rights reserved (CC BY), https://www.flickr.com/photos/dhobern/14009150095/
  3. (c) William Avery Hudson, some rights reserved (CC BY-NC-ND), https://www.flickr.com/photos/williamaveryhudson/18068200943/
  4. (c) Wendell Smith, some rights reserved (CC BY), https://www.flickr.com/photos/wendellsmith/8749709961/
  5. Adapted by Jonathan Parker from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Alliaria_petiolata
  6. (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Alliaria_petiolata
  7. (c) gburg2016, some rights reserved (CC BY-SA), http://www.inaturalist.org/guide_taxa/380442

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