Pardon Me, Do You Have Any Garlic Mustard?

With a name like garlic mustard, you would think it would come in a tiny overpriced jar and be delicious in a sandwich. Its leaves do have a light taste of garlic and could be used for cooking. But if you do, proceed with extreme caution! Garlic mustard (Alliaria petiolate) is an invasive species in North America, and it isn’t worth spreading it in exchange for a tasty snack!

What is garlic mustard?

Garlic mustard is a biennial herbaceous plant part of the Brassicaceae family, which includes crucifers, cabbages and, of course, mustards. It’s first year, it forms small round rosettes of kidney-shaped leaves. As its toothed leaves are evergreen, they emerge from the snow with a distinct advantage over native plants. In the spring of its second year, it will produce one or more flowering stalks approximately 1 m in height, topped with small white four petaled flowers and its upper leaves will become triangular and jagged. By the beginning of summer, the plant has already produced four-sided seedpods and died. Each plant produces an average of 600 seeds, but as much as 7900, wherein lies the problem.

Origins and Spread

Garlic mustard is native to Europe and parts of Asia and, you guessed it, it was brought to North America by European settlers in the 19^th century. It was grown here as a herb and for medicinal purposes. It escaped cultivation and has now spread in a majority of American states and to Canada, in British Columbia, Ontario and Quebec.

Although garlic mustard tends spread in disturbed areas, it can also invade undisturbed forests as well and displace native plants. As it emerges quickly in the spring and is fast growing, it outcompetes surrounding plants. It is also highly adaptable, supporting a wide range of growing conditions. While garlic mustard has predators in its native habitat, it has none, contributing to its spread.

Luckily, its seeds are not frequent flyers and tend to stay close to home. Wind and water dispersal are not a significant problem. What is an issue, however, is spread by humans and animals, including pets. Seeds can cling to clothing, boots and fur and be inadvertently dispersed to new areas.  For this reason, garlic mustard is quite common along recreational trails.

Impact

As mentioned above, garlic mustard grows and comes to seed quickly, forming dense beds that suffocate native plants by outcompeting them for light nutrients and water. On top of that, it is allelopathic, releasing chemicals which impede the growth of surrounding plants. These chemicals could also impede the beneficial symbiotic relationship some plants form with fungi, further harming local plat populations.

It is also thought that the rapidly decomposing leaves of garlic mustard can affect the amount of leaf litter in an infected area. As it decays faster than native plants, it can reduce the amount of leaf litter and negatively impact local ecosystems, and the flora and fauna that depend on them.

Identification

Properly identifying garlic mustard is an essential first step to its eradication as it can be mistaken for other natives and non-natives. In its first year of life, it’s kidney-shaped leaves can be mistaken for native violets but also for the invasive creeping Charlie (Glechoma hederacea). It is easily identifiable by its leaves, however, which smell of garlic when crushed. Its second year it can be distinguished from other similar plants by its triangular toothed leaves, as their flowers tend to be similar.

Control

There is no easy way around removing garlic mustard and, I’m sorry to say, it will probably require some hand pulling! There are 4 main control measures:

• Hand pulling
• Mowing or cutting
• Removing flower heads
• Herbicide

The best method to use will depend on the size of the infected area. Small pockets of garlic mustard can be removed by hand or cut down with a lawn mower or other machine. Removing flower heads is another effective method as it will prevent the spread of seeds and plants will die shortly after. Debris should be double bagged and left in the sun for a few days to ensure plants have been properly neutralized. DO NOT COMPOST! Seeds can survive the composting process and cause further spread.

After working with garlic mustard, be careful not to disperse seeds that may have clung to your boots and clothes. Remove them as soon as possible and wash clothes thoroughly. Boots can be brushed to eliminate any remaining seeds.

Larger Infestations

For larger infestations, mowing remains a viable option, but (and I hate saying this) use of herbicides may be required if the infestation cannot be controlled. I highly suggest contacting a professional and local authorities before considering the use of herbicides as they will also harm the local flora and fauna. The presence of rare and at-risk species should be verified beforehand and a plan to restore native plants is highly recommended. Controlled burning is another option, but again, contact professionals and local authorities in case of major infestations.

Garlic mustard seeds can remain viable for up to 5 years in soil, so any control method you choose will likely need to be repeated for several years. I would not recommend harvesting as a method of control because of the risks of further dispersing seeds.

Prevention

Very little can be done to prevent the spreading of garlic mustard. If possible, do not disturb forested areas as this may be a possible entry point for infestation. Also, learn to identify garlic mustard while hiking as humans are an important vector for its dispersal.

There is light at the end of the tunnel, as small populations of aphids (identified as Lipaphis pseudobrassicae but could also be the European Lipaphis alliariae) feeding on garlic mustard have been found in Connecticut, Massachusetts, Michigan, Minnesota, Ohio and Wisconsin. The dark green insect feeds on the sap of the plant causing wilting of leaves and twisting of seed pods. Biomass of this invasive plant is lower in areas with this aphid. There are also European weevil species (Ceutorhynchus spp) being investigated as biological means of controlling garlic mustard.