The Invasion of Garlic Mustard

6/1/2002

Wisconsin DNR / WGA

Much of this material is from the Wisconsin DNR.

There are many names for this invading weed: Alliaria petiolata, garlic mustard, hedge garlic, sauce-alone, jack-by-the-hedge, poor man’s mustard, jack-in-the-bush, garlic root, garlicwort, mustard root. It looks rather pretty in the woods, but if it gets its way, it may be the only plant you see in the woods. Many of us have commented on how prevalent this plant is this Spring. Many agencies, including the Wisconsin DNR, are seeking assistance in curtailing its spread. Many locations are hosting Pulling Parties hoping for the assistance of volunteers to remove this invader.

Impact

Garlic Mustard is a rapidly spreading woodland weed that is displacing native woodland wildflowers in Wisconsin. It dominates the forest floor and can displace most native herbaceous species within ten years. This plant is a major threat to the survival of Wisconsin’s woodland herbaceous flora and the wildlife that depend on it. There are two modes of spread: an advancing front, and satellite population expansion possibly facilitated by small animals. Unlike other plants that invade disturbed habitats, garlic mustard readily spreads into high quality forests.

Recognizing

Garlic mustard is a cool-season biennial herb that ranges from 12 to 48 inches in height as an adult flowering plant. Leaves and stems emit the distinctive odor of onion or garlic when crushed (particularly in spring and early summer), and help distinguish the plant from all other woodland mustard plants. First year plants consist of a cluster of 3 or 4 round, scallop edged leaves rising 2 to 4 inches in a rosette. Second-year plants generally produce one or two flowering stems with numerous white flowers that have four separate petals. Garlic mustard is the only plant of this height in our woods with white flowers in May.

Spread

Garlic mustard is an exotic species introduced from Europe presumably by early settlers for its supposed medicinal properties and for use in cooking. It is widely distributed throughout the northeastern and Midwestern U.S. from Canada to South Carolina and west to Kansas, North Dakota, and as far as Colorado and Utah. In Wisconsin, the plant is currently concentrated in the southeastern and northeastern counties, although distribution records indicate its presence is nearly statewide. The invasion of forests usually begins along the wood’s edge, and progresses via streams, campgrounds, and trails.

This species is a biennial that produces hundreds of seeds per plant. The seeds are believed to be dispersed on the fur of large animals such as deer, horses, and squirrels, by flowing water and by human activities. In our areas, seeds lie dormant for 20 months prior to germination, and may remain viable for five years. Seeds germinate in early April. First-year plants remain green through the following winter, making it possible to check for the presence of this plant in your woods throughout the year. Garlic mustard begins vegetative growth early in the spring, and blooms in southern Wisconsin from May through early June. Fruits begin to ripen in mid-July, and are disseminated through August. Viable seeds are produced within days of initial flowering.

Removal

Minor infestations can be eradicated by hand pulling at or before the onset of flowering, or by cutting the flower stalk as close to the soil surface as possible just as flowering begins (cutting a couple inches above ground level is not quite as effective). Cutting prior to this time may promote resprouting. Cutting flowering plants at the ground level has resulted in 99% mortality and eliminates seed production. A scythe, monofilament weed whip, or power brush cutter may be helpful if the infestation covers a large area. When pulling, the upper half of the root must be removed in order to stop buds at the root crown from sending up new flower stalks. Pulling is very labor intensive, and can result in soil disturbance, damaging desirable species, and bringing up seeds from the seed bank. These results can be partially prevented by thoroughly tamping soil after pulling. If, however, seed bank depletion is desired, leave the soil in a disturbed state to encourage further germination, and return annually to remove the plants. In general, cutting is less destructive than pulling as a control method, but can be done only during flower stalk elongation. Pulling can be done at any time when the soil is not frozen. If flowering has progressed to the point that viable seed exists, remove the cut or pulled plants from the area. Where populations are established, seed production must be prevented for 2-5 years to deplete the seed bank.

You can help

Sometimes, the DNR sponsors workdays where volunteers come and help pull garlic mustard. Garlic mustard is spreading rapidly at several state parks and trails. Browntown-Cadiz Springs State Recreation Area, (608) 966-3777, and Blue Mound State Park, (608) 437-5711, need help pulling the invasive weed. (5/22/02) The Glacial Drumlin State Trail (exit DNR) also wants help in pulling garlic mustard. According to Department of Natural Resources Naturalist Tom Davies, “This is the worst year I have seen for the spread of garlic mustard along the trail. This is a great opportunity for those who care about the trail and the environment to provide community service. Individuals, groups, or organizations are all welcome, and very much needed. An hour, a day, or whatever time you can spare will make a difference.” To volunteer your time in this important project, call Tom Davies or Andy Krueger at (920) 648-8774. (5/20/02) Anyone interesting in pulling garlic mustard while hiking the trails at Governor Dodge State Park is more than welcome. The park will furnish the garbage bags. Any groups who are interested in coming out to the park and having a “garlic mustard pulling party” are encouraged to contact the park, (608) 935-2315. (5/11/02)