 Garlic
Mustard (Alliara Petiolata)
By David Wehde, JCCB Vegetation Specialist
Description: Garlic mustard is
a cool-season biennial herbaceous plant that grows
to a height of 12 to 48 inches at flowering. Leaves
and stem produce a strong aroma of garlic when crushed.
As a biennial, garlic mustard requires two growing
seasons to complete its life cycle. First year plants
appear as a rosette of three to four round, scallop-edged
leaves, rising approximately four inches above the
ground.
Second-year plants produce one or two flowering
stems, each stem bearing numerous white, four-petalled
flowers. Fruits are slender capsules, one to two
inches long, which produce a single row of black
oblong seeds. Viable seeds are produced within days
of initial flowering. Hundreds of seeds are produced
by a single plant. The dispersal mechanism of this
species is believed to be by large animals, flowing
water and by human activities. Seeds remain viable
in the soil bank for up to five years.
Distribution: Garlic mustard is
an exotic species introduced from Europe by early
settlers for its so-called medicinal effects and
for use in cooking. It is a widely distributed weed
found throughout the northeastern and midwestern
United States from Canada to South Carolina and
west to Kansas, North Dakota, and as far west as
Utah. In Iowa major concentrations of this plant
can be found in the eastern half of the state.
Habitat: Garlic mustard can be
found in upland and floodplain forests, savannas,
roadsides or in your yard or garden. It is a shade
tolerent species but can be found in sunny habitats.
It is intolerant of acidic soils.
Effects of the Invasion: With the
ability to spread rapidly, garlic mustard is a major
threat to the survival of forest and savanna, herbaceous
flora and the many species of wildlife that are
completely dependent on these species. It dominates
the forest floor and can displace most native forbs
within ten years. What makes garlic mustard especially
alarming is the fact that this species invades undisturbed
habitats and readily spreads into high quality woodlands
and savannas.
Controlling Garlic Mustard - Mechanical
Control Methods
Pulling: Minor infestations can be eradicated
by hand pulling at the onset of flowering or before.
If flowering has progressed to the point when viable
seed is present, carefully remove the plant from
the area.
Disadvantages of Pulling: Pulling
garlic mustard is very labor intensive, and can
result in soil disturbance, damage to desirable
species and bringing up seed from the seed bank.
Cutting: Larger infestations of
Garlic Mustard can be eradicated by cutting
the flower stalk as close to the soil surface as
possible just as flowering begins. Cutting
at the ground level has resulted in up to 99% mortality
of plants and eliminates seed production. A power
monofilament weedeater works well for large infestations.
As with pulling, if plants have set seed they must
be carefully removed from the area so that seeds
are not dispersed.
Disadvantages of Cutting: It can
only be done during flower stock elongation. In
many cases, non-target species are also cut in heavy
infestations.
Prescribed Burning: Fall and early
spring burning may be effective in controlling garlic
mustard. First year plants are killed by fire if
leaf litter is completely consumed during fire event.
Up to five years of prescribed burning may be required
to bring infestations under control.
Disadvantages of Prescribed Burning:
Bare soil enhances survival of seedlings that germinate
after prescribed burning and total population of
garlic mustard may increase. In practicality it
is difficult to achieve desired fire effects within
a given unit. This is because of variation in fuels,
fuel moisture conditions, topography, windspeed
and structure of the plant community itself, which
causes the heat regime of a prescribed burn to vary
significantly from unit to unit and from year to
year.
Other control methods-
Chemical Control: Infestations
of garlic mustard can be controlled by the use of
glyphosate or triclopyr in a solution with water.
This is best done in the fall or early spring when
most native plants are dormant but garlic mustard
is green and vulnerable.
Disadvantages of Chemical Control:
Herbicides in general are non-selective, applicators
must use caution during application so non-target
species are not harmed. Read the label and follow
all instructions when working with all pesticides.
Biological Control: Several fungal
pathogens, which affect garlic mustard, have been
identified. Greenhouse studies of Fusarium
solani resulted in significant garlic mustard
mortality due to basal stem rot and root rot; research
on field applications are continuing.
Control methods listed will vary from site to site.
To determine what technique to deploy will depend
on several variables, including site location, current
environmental conditions, long term management objectives
for the unit in question and expenditure of labor
and resources. In practicality, several different
control methods should be combined to reduce the
garlic mustard population to a level in which native
plant populations will be allowed to exist.
Reference:
Kerns, Kelly Wisconsin Manual of Control Recommendations
for Ecologically Invasive Plants, Bureau of
Endangered Resources, Wisconsin Department of Natural
Resources, pp. 27-28, May 1997.
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