This
information courtesy of the Colorado Natural Areas Program
Family:
Brassicaceae (Mustard)
Other
Names: woad
USDA
Code: ISTI
Legal
Status: Colorado Noxious Weed List A
Not common in Colorado – Notify your county weed supervisor if you
discover this plant!
Identification
Growth
form: Winter annual, biennial, or short-lived perennial forb
Flower:
Flowers are bright yellow and clustered.
Seeds/Fruit:
Seedpods are black or purplish-brown, one-celled, with a single
seed.
Leaves:
There are two types of leaves, basal and stem. The basal rosette
leaves are 3-4 in, oblong, lance-shaped, and connected to the stem
by a petiole. The upper stem leaves are simple, alternate,
bluish-green, with a whitish nerve on the upper surface of the
blade. These leaves clasp the stem with ear-like projections, and
decrease in size toward the top of the stem. All leaves have a
slight pubescence and are nearly entire, but occasionally toothed
Stems:
Mature plants are 12-48 inches tall.
Roots:
It has a thick taproot that may exceed five feet in length.
Seedling:
No information available.
Similar Species
Exotics:
None known.
Natives: None known.
Impacts
Agricultural:
Dyer’s woad reduces forage production in crop and rangelands.
Ecological:
Dyer’s woad is an aggressive weed that infests disturbed and
undisturbed sites and then spreads outward into crops and rangeland. The BLM projects that infestations of
dyer’s woad increase 14% annually, and the Forest Service believes
that it has increased several fold on Intermountain forests during
the past three decades. There is some evidence that
dyer’ woad produces allelopathic chemicals.
Habitat and Distribution
General
requirements: Dyer’s woad appears to be well adapted to the
physical and environmental conditions of the Intermountain states. It is especially well suited to dry, rocky, soils
common to many steep hillsides throughout the western United States.
Infestations are frequently observed in rugged inaccessible mountain
terrain. Dyer’s woad is also commonly found on
disturbed sites, along roadsides, waste areas and rights-of-way.
Distribution:
Not yet present in Colorado. Current distribution in the United
States includes Virginia, West Virginia, northern Utah, southeastern
Idaho, western Wyoming, northern California, southeast Oregon,
Montana, and Nevada.
Historical:
In Europe, dyer’s woad has been cultivated as a source for blue
dye and for medicinal properties since the 13th century.
Biology/Ecology
Life
cycle: Established dyer’s woad plants begin growth early in the
year. The plant has a deep tap root as well as roots near the soil
surface. Early growth plus the two-tiered root system probably
account for its competitive ability.
Undisturbed dyer’s woad plants behave as biennials or winter
annuals and typically require portions of two growing seasons to
produce seed. Dyer’s woad germinates in the fall or early spring.
The seedlings develop rosettes that produce large taproots during
the first year. During the winter the plants undergo vernalization.
The following spring, new leaves grow from the crown bud in the
rosette, and bolting begins. Flowering occurs in late spring, with
the exact timing dependent upon elevation.
Mode
of reproduction: Reproduces by seeds.
Seed
production: Hundreds of seedpods, each containing one seed, are
produced anywhere from 4-6 weeks after flowering begins.
Seed
bank: Seeds do not remain viable in the soil for long periods of
time.
Dispersal:
No information available.
Integrated Management
Summary
Within
the last century dyer’s woad has become a serious problem on
rangelands and croplands of the United States. It
is not yet established in Colorado, so the most important control is
to be on the lookout for it and prevent new infestations. If
infestations are discovered, they should be controlled immediately,
and all seed production prevented. Report occurrences of this plant
immediately to the county weed supervisor. Dyer’s woad is an
important range weed since it competes favorably with shrub and
browse species characteristic of rangelands. This
species typically enters areas by moving along highways, railways,
or canals, and then spreads into adjacent areas. Land managers and
others should be trained to identify the weed and remove them as
soon as possible to prevent establishment. Eliminate seed production
by pulling the plants in flower, and continue control efforts until
the soil seed bank is depleted.
References
Evans,
J.O. 1991. The importance, distribution, and control of
Dyer’s woad (Isatis tinctoria). Noxious Range Weeds. Edited by L.F.
James, J.O. Evans, M.H. Ralphs, and R.D. Child. Westview Press,
Boulder.
McConnell, E.C., J.O. Evans and S.A. Dewey. 1999. Dyer’s woad. In:
R.L. Sheley and J.K. Petroff (eds.) Biology and management of
noxious rangeland weeds. Oregon State University Press, Corvallis.
pg. 231-237.
Whitson, T.D.(ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E.
Nelson, R.D. Lee, R. Parker. 1996. Dyer’s woad. Weeds of the West.
Western Society of Weed Science, in cooperation with the Western
United States Land Grant Universities Cooperative Extension
Services, Newark CA. pg. 228.
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