Answer: 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 hand-pulling garlic mustard, the upper half of the root must be removed to prevent buds at the root crown from sending up new flower stalks. Pulling can result in soil disturbance, damaging desirable species, and bringing up garlic mustard seeds from the seed bank which then germinate. This can be partially prevented by thoroughly tamping the 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 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. Because seeds remain viable for five years, it is essential that an area be monitored and plants removed for at least five years after the initial control efforts.
For larger infestations, fall or early spring burning may be effective. First-year plants are killed by fire, if the fire is hot enough to remove all leaf litter. However, the bare soil enhances survival of seedlings that germinate after the fire, and the total population may increase after burning. Dense populations may be controlled most effectively by fall burning, when leaf litter provides adequate fuel. Spring burns should be conducted early enough to minimize possible injury to spring wildflowers. Three to five years of burning are required, and should be followed by hand-pulling or cutting of small populations produced from the seed bank. Garlic mustard plants hit by fire are generally killed. Because most woodland fires are patchy, flame torches may be useful in areas not burned in entirety.
Severe infestations can be controlled by applying a 1 to 2% solution of Roundup or Touchdown (glyphosate) to the foliage of individual plants and dense patches during late fall or early spring. At these times most native plants are dormant, but garlic mustard is green and vulnerable. Glyphosate is a nonselective herbicide that will kill or injure all green nontarget plants if it comes into contact with them. Use caution during application, and do not spray so that herbicide neither drips from the garlic mustard leaves nor drifts onto adjacent desired vegetation. Other herbicides that control mustards are expected to also control garlic mustard. This includes 2,4-D, triclorpyr (Garlon) and the combination of these products (sold as Crossbow). Herbicide use is safest for native plants if done during the dormant season, as garlic mustard will grow as long as there is no snow cover and the temperature is greater than 35 degrees F.
Good luck with your eradication project!
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