Garlic Mustard - Invasive in Wisconsin

This spring, garlic mustard (Alliaria petiolata) was spotted blooming in perennial beds in the yard. Some research helped determine how to deal with this "Restricted Invasive".

Garlic mustard is an herbaceous biennial with stems 1–4’ tall as flowering plant. First-year plants form a basal rosette that remains green through the winter. Second-year plants produce one to several flowering stems.
Legal classification in Wisconsin: Restricted
Leaves: First-year plants are 2–4” tall rosettes with 3–4 heart-shaped leaves, with a toothed margin. Second-year plants produce a flowering stalk with alternate, triangular leaves that are 2–3” wide. Foliage emits a distinct onion or garlic smell when crushed.
Flowers: Late spring to early summer of second year, producing numerous small, white, four-petaled flowers.
Fruits and seeds: Fruits are slender capsules (siliques) 1–2.5” long and contain a single row of oblong black seeds with a distinct ridge.
Roots: Taproot that often has a distinctive S-shaped curve near the top of the root.
Similar species: Creeping charlie (Glechoma hederacea) is often confused with garlic mustard, but its prostrate growth with stolons allows for differentiation from garlic mustard.
Ecological threat:
• Invades upland forests, floodplain forests, savannas, yards, and roadsides.
It is typically found in shaded areas,
but can be found in full sun. Invasion of forests usually begins along the wood’s edge, and progresses via streams, animal trails, and disturbed areas.
• Exudes antifungal chemicals into the soil that disrupt associations between mycorrhizal fungi and native plants, suppressing native plant growth.

Non-chemical control-Removal
Effectiveness in season: 90–100% Season after treatment: < 50%
Pulling or cutting the root from the stem before flowering are effective individual plant control techniques. Pull if soil conditions allow for the removal of the taproot. Pulling second-year plants is easier than pulling first-year rosettes. Alternately, cut the entire taproot with a sharp shovel or spade 1–2” below the surface. If flowers are present, bag material and dispose of it in a landfill to avoid potential for seed spread.  Repeat any control method for several years since garlic mustard seeds can survive in the soil for up to 7 years.  Hand-pull small infestations, but do not compost the plants because most compost piles do not get hot enough to kill the seeds.  Dispose of pulled plants by burying deeply in an area that will not be disturbed, or landfilling.  Call the Bureau of Endangered Resources at 608-266-7012 if you need permission to landfill garlic mustard.  To burn collected plants, burn them while still moist, because dried garlic mustard seedpods can burst open and spread the seed.

Chemical Removal:

If infestations are mixed with desirable vegetation, applications of herbicides without soil activity in the late fall through early spring can reduce injury to desirable plants since garlic mustard emerges earlier and goes dormant later than most desirable vegetation. A 1-2% solution of a glyphosate-containing herbicide is very effective.  Glyphosate is a nonselective herbicide, so avoid spraying nontarget plants.