Garlic Mustard (Alliaria petiolata)
Imported as an edible green by European settlers, this biennial shade-tolerant species dominates the groundcover of deciduous forests and disturbed areas such as flood plains, stream banks, and roadsides. Since its introduction to North America in the 1800’s, Garlic Mustard has gradually spread1. It is now widespread across southern and eastern Ontario, and is found as far south as North Carolina and Kentucky in the United States. Isolated populations have also been found on the west and east coasts of Canada2. Garlic Mustard is found throughout the Credit River Watershed.
In its first year, Garlic Mustard grows as a relatively small basal rosette of kidney shaped leaves, that can be mistaken for native violets. However, it can be easily distinguished by the distinct garlic odour present when the leaves are crushed. In its second year, Garlic Mustard grows a flowering stalk up to 1 m in height, bearing clusters of 4-petaled white flowers in spring2. Each plant is capable of producing hundreds of seeds which remain viable in the soil for up to 10 years3. Seeds can be dispersed by flowing water as well as by birds, animals, and people.
First year growth
Second year growth
Invasion of forests usually begins along the forest edge, and spreads along watercourses and trails. An aggressive competitor, Garlic Mustard is able to alter soil chemistry, making it unfavourable for many native plants, and its early spring growth crowds out species such as trilliums, violets, Wild Ginger, and many tree seedlings. Consequently, Garlic Mustard eventually dominates the understory, often forming dense single-species stands in invaded sites4.
Once Garlic Mustard has become established at a site, control methods need to be repeated every year until the existing seed bank is exhausted, or the population may re-establish itself and spread. Early detection and removal of Garlic Mustard before the first generation of seeds is produced, is therefore the best way to prevent its establishment.
Hand pulling of second year plants before they seed is a recommended control method. Cutting large patches can also reduce seed production but must be monitored as plants will resprout from the tap root. Chemical control of basal rosettes is also effective, but still requires return visits to deplete seed bank.
For more information on Garlic Mustard, please contact CVC via email or to report sightings of Garlic Mustard call the Ontario Federation for Anglers and Hunters Invasive Species Hotline at 1-800-563-7711 and add the sighting to the EDDMaps Ontario website.
https://www.youtube.com/watch?v=kfx4AFK3JF0 (Video created by Credit Valley Conservation)
https://www.youtube.com/watch?v=HaXHR_Zddhs (Video created by Ontario’s Invading Species Awareness Program)
Links for Further Information:
Ontario Invasive Plant Council’s “Garlic Mustard (Alliaria petiolata): Best Management Practices in Ontario”: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2016/07/OIPC_BMP_GarlicMustard.pdf
Ontario Invasive Plant Council’s “Garlic Mustard (Alliaria petiolata) Best Management Practice Technical Document for Land Managers”: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2017/05/OIPC_TechnicalBMP_GarlicMustard_Apr282017_D5_WEB.pdf
- Ontario Invasive Plant Council. “Garlic Mustard: One of Ontario’s Most Un-Wanted Invasive Plant Species”. Web. 15 August 2018. https://www.ontarioinvasiveplants.ca/wp-content/uploads/2016/07/unwantedlettersGarlicMustardFINAL.pdf
- Ontario’s Invading Species Awareness Program. 2012. “Garlic Mustard (Allaria petiolata)”. Ontario Federation of Anglers and Hunters. Web. 14 August 2018. http://www.invadingspecies.com/garlic-mustard/
- Rodgers, V.L., Stinson, K.A. and A.C. Finzi. 2008. Ready or Not, Garlic Mustard is Moving In: Allaria petiolata as a Memeber of Eastern North American Forests. BioScience 58 (5): 426-436. Web. 15 August 2018. https://academic.oup.com/bioscience/article/58/5/426/234892
- Rowe, P. and J.M. Swearingen. 2005. “Fact Sheet: Garlic Mustard.” Plant Conservation Alliance’s Alien Plant Working Group. Web. 14 August 2018. https://www.invasive.org/weedcd/pdfs/wgw/garlicmustard.pdf