Garlic mustard is a member of the Mustard family (Brassicaceae). It has a biennial lifecycle, therefore it takes the species two years to fully mature and produce seed. Seeds germinate in February to early March of the first year. In the plant’s first year, the basal rosette of liver-shaped, light green leaves is formed. In the second year, a tall, bolting stem is produced with more triangular leaves that are strongly toothed along the margins. (5) Garlic mustard dies back before midsummer in the Hudson Valley, leaving only withered stalks and seed heads visible. The herb is most easily visible in early spring as it leafs out before most native understory plants, washing the spring landscape in bright green. (2) Flowers of garlic mustard are small, four-petaled, white, and born in small clusters at the end of a long, mostly hairless, bolting stem.(5) Flowers develop into elongate, green pods which dry and turn brown-tan, opening to reveal many tiny very glossy, black, round seeds. (5) The leaves of garlic mustard smelly "garlicky" when crushed regardless of age, although the first year leaves typically have a stronger garlic smell.
Garlic mustard is an invader of forest understories. This nonnative herb can form dense stands that have the potential to control light, water, and nutrient resources, and thus outcompete native herbs that occupy a similar niche. Laboratory studies suggest that the nonnative herb is allelopathic, releasing chemicals that prevent the growth of competing grasses and herbs. Field studies show that removal of garlic mustard leads to increased diversity of other species.
There is currently no single optimal biological control agent in use against this species, although a handful of promising target agents are being investigated. (8)
Manual or Mechanical Control
Pulling / Digging Up: Pulling by hand is an effective method of control as long as the entire root is extracted from the soil. If garlic mustard’s taproot is left behind, the plant can re-sprout. (7)
Mowing: Mowing or weed whacking is time consuming and requires repeat treatment. Although a high percentage of plants will be killed in the first or second mowing taproots left in the soil can re-sprout. (7)
Girdling: Not applicable
Prescribed Fire: Seedlings will be killed by early spring fires. Second year garlic mustard has a long taproot, rendering it resistant to fire, unless the burns are moderate to high intensity (2)
Prescribed Grazing: Garlic mustard is a palatable, but not preferred, forage species for livestock and whitetail deer. In fact, deer preferentially grazing other species may help boost garlic mustard’s establishment in eastern forests. (2)
Soil Tilling: Not advisable in natural areas. Tilling may fragment taproots and encourage re-sprouting. It will also expose more seeds for germination. (10)
Mulching: Mulching may help reduce the seed bank and cover bare ground after infestations of garlic mustard have been controlled via spraying and or pulling, however, this will also reduce the reestablishment of other, native vegetation in the area, too. (9)
Solarization: Not applicable
Hot Foam Spray: Not applicable
The pesticide application rates and usage herein are recommendations based on research and interviews with land managers. When considering the use of pesticides, it is your responsibility to fully understand the laws, regulations and best practices required to apply pesticides in a responsible manner. At times, the pest you seek to treat may not be on a pesticide label, requiring a 2ee exemption from NYSDEC. Always thoroughly read the label of any pesticide and consult the NYSDEC or a licensed pesticide applicator with questions.
Foliar Spray: A 1-2% solution of glyphosate or triclopyr is effective at managing garlic mustard, although repeat spot applications may be necessary. Infestations managed in this way should be revisited in 2-3 weeks to monitor for regrowth. Early spring spraying, before other ephemeral plants have leafed out will provide the greatest management efficacy and the least collateral damage of non-target species. Always read and follow all instructions on the herbicide label. (10)
Cut Stump: Not applicable
Basal Bark: Not applicable
Stem Injection: Not applicable
Pre-Emergent Spray: Not applicable
General management overview and recommendation
As with any other invasive infestation complex, large stands of garlic mustard are best managed via a combination of mechanical and chemical means. All managed infestations should be monitored for at least six years to ensure exhaustion of the seed bank and to prevent reinvasion from nearby populations. (2). Any new seedlings can be hand pulled or sprayed. As an extremely common invasive in the region with a very high reproductive potential, it may be more fruitful to simply keep this species out of areas where known vulnerable species are established and may be impacted by garlic mustard’s presence. (7)
Post treatment monitoring
Any infestations managed by chemical means must be revisited in 2-3 weeks to check for treatment efficacy. Infestations managed solely by mechanical or physical means will need follow up treatment each spring for four to six years to ensure exhaustion of the seed bank. (2)
Waste material can be burned, solarized and/or composted so long as management was completed prior to seed set. Any fruit must be bagged and disposed of. (7)