[Isatis tinctoria L.][ISATI][CalEPPC:
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Map of Distribution
SYNONYMS: Marlahan mustard
DESCRIPTION: Erect biennial, sometimes
winter annual or short-lived perennial, to 1.2 m tall. Immature plants exist
as basal rosettes until flowering stems develop at maturity. Plants are highly
competitive and often grow in dense colonies. Dyers woad is primarily
a noxious weed of rangeland, agronomic crops, and undisturbed natural areas
in the intermountain west region of the northwestern U.S. It was cultivated
for several centuries in Europe as a medicinal herb and source of blue dye.
Foliage contains compounds that appear to have insecticidal and fungicidal
properties. The native rust [Puccinia thlaspeos] can significantly
reduce seed production and may have potential as a biocontrol agent. Dyers
woad was introduced from Europe as a cultivated plant of the early settlers
of the Eastern U.S.
SEEDLINGS: Cotyledons ovate, glabrous, ~ 15-20 mm long. Tips +/- squared,
often slightly indented. Bases +/- wedge-shaped, tapering into a stalk ~ 5-12
mm long. First leaves alternate, elliptic to obovate with smooth margins,
~ 15-20 mm long, +/- rounded at the tip, sparsely covered with long hairs.
Bases taper to a hairy stalk ~ 4-10 mm long. Subsequent few leaves resemble
PLANT: Flowering stems typically several
per rosette, gray to purplish, glabrous, typically branched near the top.
Leaves +/- bluish-green, often covered with a powdery white bloom (glaucous).
Midveins conspicuously pale. Rosette leaves oblanceolate
to elliptic, ~ 3-18 cm long, 1-4 cm wide, tips +/- rounded, bases gradually
tapered to stalk ~ 1/2-3/4 the length of the blade, sparsely covered with
simple long hairs, especially on veins. Margins weakly toothed to +/- wavy.
Stem leaves alternate, sessile, broad to narrowly arrowhead-shaped (sagittate)
with smooth margins, sometimes broadest near the tip, clasping and lobed at
the base, +/- glabrous.
and UNDERGROUND STRUCTURES: Taproots of
rosette and mature plants penetrate the soil to an average depth of about
1 m. Most lateral root growth occurs in the top 30 cm of soil during the second
FLOWERS: April-June. Panicles of racemes +/- flat-topped (corymb-like)
or umbrella-shaped. Petals 4, bright yellow, spoon-shaped, ~ 3-4 mm
long. Sepals 4, separate to base, shorter than petals. Stamens 6, 4 long,
2 short. Insect- or self-pollinated.
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and SEEDS: Fruits (silicles) pendant,
black to blue- or purplish-black, flattened, oblong to oblanceolate, 8-18
mm long, 5-7 mm wide, longitudinally ridged at the center of each side, gradually
tapered to a slender stalk. Stigma sessile. Fruits do not open, mostly
contain 1 seed. Seeds oblong, +/- round in cross-section, grooved into 2 unequal
halves, dull yellowish- to orangish-brown, ~ 3-4 mm long.
CHARACTERISTICS: Dried plants with a few
fruits may persist well into winter.
HABITAT: Disturbed and undisturbed sites, roadsides, railroad rights-of-ways,
fields, pastures, grain and alfalfa fields, forest and rangeland. Often grows
on dry, rocky or sandy soils.
DISTRIBUTION: Klamath Ranges, Cascade Range, North Coast Ranges, northern
& central Sierra Nevada, Modoc Plateau, northern San Francisco Bay region;
to Oregon, Montana, Utah. To 1000 m (3300 ft). Expanding range in the intermountain
PROPAGATION/PHENOLOGY: Reproduces by seed. Most fruits fall near the parent
plants, but some fruits disperse short distances with wind and to greater
distances with water, soil movement, human activities, as a seed and hay contaminant,
and possibly by clinging to the fur or feathers of animals. Seeds mature about
8 weeks after flower stem initiation. In a Utah study, plants produced an
average of 383 fruits per plant. Seeds removed from fruits lack a dormancy
period. Fruit coats contain water-soluble inhibitors that prevent many seeds
from germinating until leaching occurs and reduce seedling growth of dyers
woad and other species. Some seeds germinate in the presence of the inhibitor.
Rupture of fruit coats increases germination. Seeds germinate in fall and
early spring. At maturity, fall-germinating plants typically produce more
seeds than spring-germinating plants. Seed longevity under field conditions
has not been studied.
FAVORING/DISCOURAGING SURVIVAL: Plants cut
above the crown can grow new shoots and may persist as short-lived perennials.
Spring cultivation can control infestations in crop fields.
SPECIES: Dyers woad is distinguishable
from other members of the mustard family by its unique fruits.
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Dyers woad is an aggressive member
of the Brassicaceae family. Native to Southeastern Russia, Dyers woad has
been a historically important plant used in making indigo dyes. It was first
discovered in Siskiyou County, California in the Scott Valley and is believed
to have been imported in contaminated alfalfa seed from Ireland in the early
1900s. Dyers woad has spread throughout Northern California and is currently
expanding throughout the intermountain west. It is currently listed as a CDFA
Dyers woad is of concern for several reasons. It invades both disturbed and
undisturbed areas, but is most common on dry rocky soils that typically exhibit
reduced herbaceous plant cover. However, dyers woad will also invade dense
stands of medusahead, bulbous bluegrass, and cheatgrass, in a manner similar
to yellow starthistle. On rangelands, it reduces forage availability by suppressing
annual grasses and is low in palatability to grazers. Dyers woad may also
invade alfalfa and wheat fields, especially where dryland agriculture is used.
Dyers woad may behave as an annual, a biennial, or a monocarpic perennial.
Flowering is induced by cold stratification of rosettes, so late spring emerging
plants will not generally flower until the second or third year. Dyers woad
reproduces mainly by seed but may resprout from buds located at the crown.
Seed production is prolific and typically occurs from late May through July
in California. Seed remain within the fruits and are mainly dispersed by animals,
human related activities and water. The role of rodents and birds in dyers
woad seed dispersal is uncertain.
Prevention: Dyers woad has
frequently spread via contaminated hay and alfalfa, and on mowing and harvesting
equipment. Invasions initially occur along roadsides and then move into adjacent
fields or rangelands. Eliminating solitary plants along roadsides is critical
to avoid larger problems. Additionally avoid carrying contaminated hay into
backcountry areas where dyers woad does not occur.
Mechanical: Mowing is not
considered an effective treatment due to resprouting from the crown. However,
hand pulling may be very effective in reducing infestations. It is critical
to remove the crown to prevent resprouting. Hand pulling is easiest after
the plants have bolted but should be done before seed set. Most hand pulling
programs have indicated it is necessary to followup for several years to prevent
reinfestation. The longevity of the seed in the soil seedbank is currently
unclear. However, anecdotal evidence has suggested the seedbank may persist
for several years.
Chemical: Dyers woad is
very expensive to manage with herbicides on a large-scale. 2,4-D is the most
economical treatment. Plants should be treated in the seedling to rosette
stages. A one-percent solution is effective for spot treatments. Dense infestations
require higher labeled rates (1.9-2.85 lb ae/A) for control. Late season control
of flowering plants is difficult and may not eliminate seed production. Other
auxin type herbicides such as dicamba are no more effective than 2,4-D and
are not recommended.
On roadsides, chlorsulfuron (0.75 oz ai/A) may be applied preemergence or
postemergence to seedlings and rosettes. Postemergent applications should
be made with a 0.25% v/v non ionic surfactant. Late season applications when
the chances for rainfall are low are not recommended.
Biological: A native rust
pathogen, Puccinia thlaspeos, was observed to attack dyers woad in Idaho in
the late 1970's. The non-specific pathogen is still under investigation but
has been distributed to some populations in other states. The rust enters
the plant through the leaves and is systemic in nature. Severely infected
plants produce few to no seed and mortality is frequent in infected seedlings
and rosettes. This pathogen is not currently registered for use as an approved
biological control agent in California. No host specific insects have been
found for dyers woad.
Agriculture Fields: In agricultural settings, cultivation is effective
in eliminating rosettes and seedlings. Seedlings that emerge following cultivation
may be controlled with 2,4-D in cereal grains or forage grasses. In alfalfa,
hexazinone, metribuzin, and 2,4-DB are effective for controlling dyers woad.
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