Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityJune, 1997
Garlic Mustard : an invasive weed of shady places
Keywords: landscape, weed control
H aving grown up in Central Ohio and having an interest in weeds, I thought
that I had a good idea of what kinds of weeds we had in the area. Then
one day last fall, a colleague brought in a herbaceous weed with triangular-shaped
leaves that I had never seen; this plant was taking over a corner of her
garden. This was my first glimpse of garlic mustard. I didnāt think too
much about it then.
Now, to my annoyance, I see this plant almost everywhere there is some
shade, particularly along roadsides and in woodland areas. The last straw
was seeing this Johnny-come-lately aggressively taking over a hillside
of wildflowers in my parentās backyard!
Garlic mustard (Alliaria petiolata) is a native of Europe, but
now is present throughout the Midwest, Eastern US and Canada. It favors
shaded, disturbed sites, but apparently is able to move into undisturbed
woodland communities. Some research indicates it prefers higher-pH soils.
Ecologists and wildflower enthusiasts are concerned because garlic mustard
forms large stands to the exclusion of native wildflowers.
The weed is biennial; seeds germinate in the spring and form a basal
rosette of kidney-shaped leaves that will live over the winter. The leaves
in the first year resemble ground-ivy (Glechoma hederacea), but
are larger. Flowering stalks one to four feet in height form the following
spring. Clusters of unexciting, small, white, four-petal flowers appear
April through June. The leaves on the flowering stalks are triangular or
heart-shaped and coarsely toothed. When crushed, the leaves have a pervasive
smell of garlic - a great ID feature!
This is a weed to eradicate if you wish to preserve species diversity
in a woodland landscape and avoid a monoculture of garlic mustard. A one
percent solution of Roundup Pro (glyphosate) is effective on this weed.
If garlic mustard is intermixed with desirable native plants, spring and
fall are good times to selectively take out this weed. At these times garlic
mustard remains green and can take up the chemical if temperatures are
not too low, while most other plants are dormant, leafless and immune to
injury from Roundup. Mechanical control also can be an effective means
of controlling this weed. Flowering stems cut to the ground level usually
do not resprout; this is an effective approach for controlling the weed
in the flowering stage and for preventing seed dispersal, but will miss
plants currently in the rosette stage. Cut stalks should be removed because
they may set seed after cutting. Seeds of garlic mustard have a 20-month
dormancy period. Thus, at least several years of effort will be required
for eradication of this weed.
Click here to view a photo
of garlic mustard.
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Note about last monthās L.A.N.D. Column: Apologies for an error
in last monthās article on preemergence herbicides for container weed control.
Goal was described as a good choice for grassy weed control; instead, Goal
should have been described as good choice for broad-leaf weed control.
