There are a wide variety of non-native invasive plant species that have taken hold in Madison County. These plants cause harm to the environment, as well as potential harm to human, animal, and plant health in the preexisting environment. Some of these damages can be caused by overtaking beneficial native plants in the ecosystem, act as vectors for diseases and other invasive species, such as invasive insects, and are unhealthy or potentially toxic to native animals. In this series, we will discuss identification and control of these prevalent invasive plants.
Identifying Garlic Mustard
Garlic mustard (scientific name Alliaria petiolata) is a biennial, flowering plant in the brassica family. It is native to areas throughout Europe, Africa, and west and central Asia. This invasive plant presents two separate growth patterns depending on its stage of life. During its first year of growth, garlic mustard only reaches about 4 inches tall, and has small, rough leaves that grow in rosette-like patterns that can resemble circular or heart-like shapes. These growth patterns often cause this invasive plant to be mistaken for plants in the violet family during the first year of its growth cycle. It will retain these leaves andits vibrant green color throughout the winter months. During the second year of its life cycle, garlic mustard can grow anywhere from 2 to 4 feet in height, and grow in a triangular or cone-like shape, starting narrowly at the tip of the plant and widening in its growth the rest of the way down. The stems of this invasive plant may also appear hairy once they reach their second year of growth. The leaves of garlic mustard during this stage of growth can grow up to 3 inches long and 2 inches wide, and are heart-shaped, roughly textured, and with large toothy serrations around the edges. These leaves, as well as the stems, will produce a garlicky smell when they are crushed, contributing to the name it is known by. Garlic mustard will flower during its second season, blooming from April to May in clusters of tiny white flowers, each one less than an inch in size, with 4 petals that create the shape of a cross. These flower bunches grow at the ends of the stems, blooming in very tight clusters and beginning to separate as the plant continues to mature, creating space for the fruiting bodies that will form to spread its seeds. The fruiting bodies produced by garlic mustard appear as a 4-sided pod in a thin and long shape, appearing green when first growing on the plant and changing to a darker color such as black or brown when they reach maturity. Each of these thin pods contains two rows of shiny black seeds which are spread when the pods split open during the summer. Another identifying feature of garlic mustard that can help determine if it is present in an area is the structure of its root system. When this plant is properly pulled up by its roots, it will have a thin white taproot that extends into the ground.
Garlic mustard can survive in a wide variety of conditions and soil types. It can grow in full sun, full shade, and partial shade, and can tolerate acidic, basic, and neutral soil conditions, as well as tolerating many different moisture levels, though it prefers moist soils to optimize its growth. All parts of this plant are edible by humans, and different parts can be used in different ways of preparation. Its thin taproot tastes and smells similar to horseradish, and can be chopped up to be used in soups and stews, while the leaves can be used as greens in salads and other cooking or preparation dishes, and the seeds can be used as seasoning, similar to other mustard seeds. This invasive plant is dangerous to some native wildlife, namely certain native species of butterflies, as this plant produces a chemical that is toxic to any eggs laid on these plants.
How It Spreads
Garlic mustard was brought to the United States in the 1860s as a medicinal herb and to be used for cooking. Since that time, it has spread throughout the Northeast US, the Midwest, parts of the Southeast, and even parts of the Pacific Northwest. This invasive plant spreads exclusively through seeds. Due to the large amount of slender seed pods that each plant can produce, it allows a single garlic mustard plant to produce hundreds of seeds at a time. These seeds explode from the thin pods, firing up to 10 feet from the plant that produced them and allowing them to spread over spaces quickly, and choke out native plant life. This ballistic method of spread is likely used because the seeds are not ideally shaped to be carried by wind or water, so it allows the seeds to increase their spread, while often also being taken far distances from its origin plant by humans and wildlife. Thanks to this invasive plant’s ability to live in a wide variety of conditions, it can quickly take over areas such as roadsides, trail edges, flood plains, streambanks, and areas throughout forests, from the edges to deeper within. Garlic mustard often takes up the same environmental niche as more beneficial, native wildflowers that would occur in these areas where it has taken over, outcompeting them due to its tolerance of less than ideal conditions.
Controlling Garlic Mustard
Garlic mustard is very difficult to control once it has become established in an area, so the most effective way to prevent it from taking hold is to monitor potential habitats where it could appear and remove it when spotted. It can often be spotted in the late fall or early spring in its first year of growth with those smaller, rosette shaped leaves when the plant is still immature. In this immature stage, removing will prevent any seed from being spread by those plants, as they are not mature enough to produce them yet. If these starting infestations are small, they can be controlled with hand pulling as long as the entire taproot is carefully removed to ensure it does not resprout. If the garlic mustard found in place has reached maturity, the time of year where it will be most beneficial to remove it is early to mid-spring, before it begins to flower and produce seeds. These mature plants can also be removed by hand when infestations are small, but it is still critical that the entire root system is pulled from the ground, or the plant may resprout. Spot treating with chemical control is also a viable option, but requires precise application to prevent killing beneficial or native species that may also be present in the area. In areas with larger infestations of garlic mustard, hand-pulling is not a viable option of control. Other mechanical methods that may be viable include cutting the flowering stems off low to the ground or at ground level before they produce seeds to prevent any seed production and dispersal from taking place that year, and can be done using items like weed eaters or mowers if there are not beneficial or native plants that the landowner wants to keep on site. If the stems of mature garlic mustard are not cut low enough, the plants will still produce seeds and flowers on different leaf axils. Mowing these large infestations should continue until the existing seedbank is exhausted, meaning it could be necessary for an indefinite period of time. If chemical methods of control are chosen, a solution of 2% glyphosate can be sprayed in a foliar application over the infestation. Be sure to thoroughly wet the leaves when using a foliar spray technique to ensure that the plant is soaking up enough of the herbicide treatment to be effective. Glyphosate is a non-selective herbicide, meaning that it will kill any and all plants within the sprayed area if desirable plants in the area are not protected. Garlic mustard can be sprayed for a successful application as long as the temperature is above 50 degrees Fahrenheit. Be sure to follow the label during any application of a pesticide product.
No matter what treatment is used, or the types of infestations they are used on, make sure the previously infested areas are monitored for any potential regrowth so it can be controlled before it establishes itself strongly again.
If you have any other questions about identifying or controlling garlic mustard, please contact the Madison County Cooperative Extension Center at (828) 649-2411, or reach out to me directly at peyton_duckett@ncsu.edu.
Citations
Invasive Species Leaflet. (2010, March). NCDA&CS, Forest Service Division. https://www.ncagr.gov/divisions/nc-forest-service/is15/download?attachmentNorth Carolina State University. (n.d.). Alliaria petiolata. North Carolina Extension Gardener Plant Toolbox. https://plants.ces.ncsu.edu/plants/alliaria-petiolata/
