Friday, February 5, 2016

Species Spotlight: Garlic Mustard

One of my favorite plants is Garlic mustard, or as it is known in science Alliaria petiolata. It was the first plant I spent a significant amount of time researching, forming the backbone of my honors undergrad thesis. This is why, despite its reputation, I will always have a fond spot for this weed. 

2nd year Garlic Mustard - Personal image
Garlic mustard is a biennial mustard native to Europe. In 1868, the first documented garlic mustard arrived in New York and thus begins an alien invasion. Genetics has suggested that garlic mustard was brought over multiple times, from multiple regions in Europe which has led to a high genetic diversity in North America.

As a biennial, garlic mustard requires 2 years to flower and produce seed. The first year is spent as a rosette, a small bundle of leaves.In the second year, the inflorescence (flowering stem) shoots up. Each plant can produce thousands of seeds. Each seed can live up to 5 years in the soil before germinating. The longevity of the seed bank is one of the reasons garlic mustard is difficult to control. It would take over 5 years of gathering every single one of those thousands and thousands of  plants that germinated from the seed bank to successfully clear an invaded area. 

Garlic Mustard with siliques (seed pods) - Personal image
Garlic mustard is able to wage chemical warfare upon other seedlings and mycorrhizal fungi. Mycorrhizal fungi is symbiotic with the roots of many plant species, they provide nutrients that the plants are unable to synthesize and vice versa. When garlic mustard invades a region the mycorrhizal fungi is greatly reduced, resulting in the death of the native plants that rely on it. For garlic mustard this is perfect, more real estate! For the invaded forest this decreases the species diversity.

As the name suggests, garlic mustard tastes like a mix of garlic and mustard. This particular  combination is disliked by the common large herbivore in North America: deer. Deer ignore garlic mustard, but eat the native plants. Clearing even more room for garlic mustard to invade!

Me taking field notes in a field of garlic mustard (white flowers)
Lots of factors have played into garlic mustard's takeover of North America, yet it is not preset across the entire continent. One of the factors that has limited garlic mustard spread is it requires a lengthy cold period for germination. The mimicking of a natural cold period in the lab is called startification. During startification, the seeds are kept moist and cold, mimicking the conditions of cold/frozen ground. This softens the seed coat so that when temperatures increase in the spring the seed germinates. Garlic mustard requires 12 - 16 weeks of startification for germination. This is what keeps garlic mustard contained to Canada and the northern US. Beyond this, there are not many other road blocks to stop this alien invasion.

The most effective control method is pulling the plants before they can make seeds. For small invasions this works well. However, garlic mustard's fast spreading rate (some predictions say >3000 miles/year) and the fact that seeds can persist for 5 years makes manual removal a difficult task for larger invasion areas. Herbicides are effective but can cause further damage to native flora. 

If you find some garlic mustard, pull it before it makes seeds. If you are feeling adventurous, you can use the plants for a number of recipes! My undergrad advisor had a soup recipe that was pretty tasty! A number of which have been put together in the Mid-Atlantic Invasive Plant Council Garlic Mustard recipe file. I haven't had the chance to try these recipe but that ricotta dip will be a must try this spring! Garlic mustard should be coming up in March/April so let me know which of the MAIPC recipes you try!

Delaware DNR made an info video about garlic mustard which I will leave you with:

  • Baskin, J. M., C. C. Baskin. 1992. Seed germination biology of the weedy biennial Alliaria petiolata. Natural Areas Journal 12(4):191-197.
  • Durka, W., Bossdorf, O., Prati, D., & Auge, H. (2005). Molecular evidence for multiple introductions of garlic mustard (Alliaria petiolata, Brassicaceae) to North America. Molecular ecology, 14(6), 1697-1706. Research Gate PDF
  •  Meekins, J. F., and B. C. McCarthy. 1999. Competitive ability of Alliara petiolata (garlic mustard, Brassicaceae), an invasive nonindigenous forest herb. International Journal of Plant Sciences 160(4):741-752.
  • Nuzzo, V. 1991. Distribution and spread of the invasive biennial Alliaria petiolata (garlic mustard) in North America. P. 137-145. In McKnight, Bill N. ed. Biological Pollution: The Control and Impact of Invasive Exotic Species. Indiana Academy of Sciences: Indiana, USA. 
  • Rodgers, V. L., Stinson, K. A., & Finzi, A. C. (2008). Ready or not, garlic mustard is moving in: Alliaria petiolata as a member of eastern North American forests. Bioscience, 58(5), 426-436. 
  • Wolfe, B. E., Rodgers, V. L., Stinson, K. A., & Pringle, A. (2008). The invasive plant Alliaria petiolata (garlic mustard) inhibits ectomycorrhizal fungi in its introduced range. Journal of Ecology, 96(4), 777-783. PDF

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