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Garlic Mustard is an exotic invasive weed, imported from Europe
that is invading the native woodland habitats in western Pennsylvania
and showing up in landscape plantings in close proximity to
woodlots. It spreads rapidly by prolific seed production and
exhibits allelopathic properties since several compounds isolated
from garlic mustard were shown to depress growth of both grasses
and herbs in laboratory experiments. The weed can become a landscape
problem if the population in the nearby woodlot is not controlled.
Garlic mustard is a biennial, a plant with a two-year life
cycle, growing its first year as a seedling and rosette stage
plant and flowering the subsequent year. Where garlic mustard
is not established, efforts should focus on detecting and eradicating
infestations before a seed bank develops. Pulling individual
garlic mustard plants by hand is the simplest and most effective
approach to managing small or isolated infestations. When pulling
plants, it is important to remove the upper portion of the roots
as well as the stem, since buds in the root crown can produce
additional stems. All pulled plants should be removed from the
site as seed ripening continues even after plants are pulled.
Repeatedly hand pulling of garlic mustard is reported to be
effective for control in small areas but has limitations. Because
seeds remain viable in the soil for up to five years, it is
important to pull all garlic mustard plants in an area every
year until the seed bank is exhausted and seedlings no longer
appear. This will require multiple efforts each year as rosettes
can continue to bolt and produce flowers over an extended period
(April-June).
Herbicides can be used to selectively remove garlic mustard
leaving the desireable plants. Application of 1-2% glyphosate
(Roundup) provides effective control of garlic mustard seedlings
and rosettes. Note: glyphosate is a non-selective herbicide
meaning that it will kill or damage most plants it comes into
contact with (including woody plants). However, to be effective,
this herbicide must be absorbed by growing leaf tissue or bark,
i.e. the plant must be actively growing. Applications in very
early spring (March-April) can often be timed for periods when
few if any other plants beside garlic mustard are actively growing.
Similarly in late fall, applications can be made with reduced
risk to many non-target species.
Information included in this article came from the Michigan
State University IPM
website.
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