In those parts of the Wisconsin where the snow has finally melted and the sun is reaching the forest floor, garlic mustard plants are awaking from their winter dormancy and soon will grow quickly. In some areas in the southern counties the first flush of seeds of this persistent weed has germinated, forming a carpet of tiny seedlings.
"Before the spring wildflowers emerge is the ideal time to search out and contain this highly invasive plant. In most woodlots it will be one of the only green plants on the forest floor this early, so it is easy to spot," says Kelly Kearns, plant conservationist for the Wisconsin Department of Natural Resources.
Kearns says that because just about all forests in Wisconsin are vulnerable to being invaded by this Eurasian transplant, every woodland owner should learn to identify it and search their woods carefully, marking and removing all plants before they go to seed in May and June.
"If only a few plants are allowed to go to seed," she notes "an infestation can rapidly get out of hand and require extensive work for many years to come."
What is at risk from a garlic mustard invasion?
Kearns says that the garlic scented plants can carpet a forest floor, crowding out native wildflowers. Tree and shrub seedlings can also be displaced, preventing long term regeneration of canopy trees and native shrubs. Recent research has shown that chemicals in the roots of garlic mustard can inhibit the mycorrhizal fungi that certain tree roots use to draw nutrients from the soil. It appears that these 2- to 3-foot tall plants have the ability to stunt the growth of trees that tower over them.
Garlic mustard (Alliaria petiolata) is a biennial herb that ranges from 2 to 40 inches in height as an adult flowering plant. Seeds germinate in spring and will show up as a carpet of small seedlings beneath the dead flowering stalks from last year. In their first year of growth the plants form a basal rosette of rounded leaves with toothed edges. They over-winter as green rosettes, giving them a boost over native plants in the spring. Second-year plants start growing as soon as the weather warms and develop flowering stems with numerous white flowers that each have four petals. In most areas of southern Wisconsin, the flower stalks are just developing and the first flowers are opening in late April to early May. By mid-June the flowers will develop seed pods with hundreds of seeds per plant. Seeds are often spread on animal fur and by human foot traffic.
There are many approaches to controlling garlic mustard, depending on the age and size of the population.
“The key to keeping garlic mustard, and most other invaders, from taking over your land is to never let them go to seed,” Kearns says.
For smaller populations and new plants that pop up away from a major infestation, hand-pulling of the second year plants is the easiest and most effective control. People can save a lot of work if they start early, as soon as the plants start to bolt, or develop a flower stalk.
“It is important to pull up the entire root or new flowering stalks will emerge. Once flowers have begun to open, it is important to remove the plants from the woods; otherwise, the uprooted plants can still develop seeds,” she says.
Most people carry heavy plastic bags, trashcans or wheelbarrows into the woods to haul out the flowering plants.
Pulled plants can be dried and burned or buried. Composting may not always kill the seed, so any finished compost should be used carefully. Generally garden waste is not allowed in landfills, but there is a temporary exception for garlic mustard and other invasive plants with seeds. Just label the bags “Invasive Plant Approved by WDNR for Disposal in Landfills.”
Larger populations can be managed with a combination of hand-pulling, herbicide and/or fire. Prescribed fires in oak forests can kill rosettes and seedlings, but may result in a flush of new seedlings that develop and will need to be controlled.
Kearns says landowners should not burn without proper training, equipment and permits. Use of fire with a high BTU propane torch with a long wand applicator is also effective, but should be done only if there is no chance of the fire spreading (ideally after a rain or when the ground and leaves are moist). Herbicides such as glyphosate or 2,4-D are effective in killing basal rosettes and seedlings if done in early spring, prior to native wildflowers emerging, or in the fall when rosettes are still active. Waiting to spray until the garlic mustard is flowering will result in more herbicide being used and more risk to native plants. Plants that have started to form seeds may continue to produce seeds even after the plants have been sprays, so start early!
More information on garlic mustard, including photos, is available on the DNR Web site. Brochures on garlic mustard may be available at local University of Wisconsin Extension offices.
Information on other invasive plants and animals, is available on the invasive species pages of the DNR Web site and on the Invasive Plants Association of Wisconsin Web site: [www.ipaw.org] (exit DNR).
People interested in learning more about what they can do about invasive species are encouraged to attend an event in June during Invasive Species Awareness Month. A schedule of events can be found at: [www.invasivespecies.wi.gov/awareness/index.asp] (exit DNR).WDNR
