Description: Garlic mustard is an invasive,
cool season, biennial herb in the mustard family. It has triangular
to heart shaped, coarsely toothed leaves that smell like garlic
if crushed. In its first year, seeds germinate early in the
spring and grow as a low rosette. After over wintering, the
rosette sends up a 2 to 4 foot tall stalk, which produces
button-like clusters of small white flowers. Each flower has
four petals in the shape of a cross. Garlic mustard begins
growth and flowering in early spring, and begins to set seed
in May and June. This plant produces abundant seed (more than
2000 per plant) which remain viable in the soil for 4-6 years.
Distribution: Garlic mustard was introduced to North
America from Europe in the early 1800’s. It was brought
here most likely for medicinal uses. It has spread into many
areas of Johnson County and Iowa. Garlic mustard predominantly
invades woodland communities, rapidly spreading and overwhelming
native woodland wildflowers and other species.
What’s The Problem?: Garlic mustard grows
early in the Spring and produces a dense carpet of plants
which shade out and rob nutrients from native woodland wildflowers
and forbs such as Dutchman’s Breeches, Spring Beauty,
and Trillium. This plant can eventually become the dominant
plant in woodlands. Garlic mustard reproduces monoeciously
(a single isolated plant can produce numerous seeds), has
a large tolerance to cold weather, and its seed dormancy varies
which allows it to avoid germination in unfavorable conditions.
Garlic mustard also produces chemicals and odors which herbivores
find disagreeable. Garlic mustard grows where access with
typical management equipment is difficult.
Management Methods: Current control methods for garlic
mustard are mechanical cutting, hand pulling, prescribed fire,
and application of burndown/systemic herbicides. Because seed
remains viable in the soil for 4-6 years, control of garlic
mustard requires a long-term commitment. Minor or initial
infestations can be hand pulled. Be sure to pull the entire
plant and root system, as new sprout can occur from small
root fragments. Plants will pull easiest if they are small
and the soil is moist. Cutting of the flower stalk soon after
flowering will eliminate seed production, and if cut at the
ground, plants will not resprout. This must be carried out
until the seed bank is exhausted, which may take several years.
If seedpods have formed before cutting, plants should be bagged
up and removed to prevent buildup of seed stores. For very
heavy infestations, applications of systemic herbicides are
also effective. Apply only to foliage or rosettes of garlic
mustard, as damage to non-target plants can occur if contacted
with herbicide. Be certain to correctly identify plants and
use the proper chemicals at labeled rates. Be sure to read
and fully understand chemical labels before usage. Prescribed
burning can be an effective tool to combat garlic mustard,
if used correctly and consistently. Fire can open up the understory
of a forest and encourage germination of garlic mustard, therefore,
annual burnings for up to 5 years may need to be done to sufficiently
kill existing plants and exhaust seed stores. Burning may
need to be supplemented with other control methods, such as
hand pulling. Biological control research is being done around
the nation to investigate other management methods for control
of garlic mustard. None are currently approved for control.