Dyer’s woad [Isatis tinctoria L.][ISATI][CalEPPC: Need more information][CDFA list: B] Photographs Map of Distribution

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SYNONYMS: Marlahan mustard

GENERAL 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. Dyer’s 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. Dyer’s 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 first leaves.

MATURE 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.

ROOTS 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 year.

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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FRUITS 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.

POSTSENESCENCE 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 west region.

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 dyer’s 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.

MANAGEMENT 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.

SIMILAR SPECIES: Dyer’s 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 Class B
noxious weed.
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.

Aspevig, K., Fay, P., and Lacey, J. 1985. Dyers woad: a threat to rangeland in Montana.
Montguide. Montana State University Cooperative Extension, Bozeman, MT
Dewey, S. A., Price, K. P., and Ramsey, D. 1991. Satellite remote sensing to predict
potential distribution of dyers woad (Isatis tinctoria). Weed Technology 5:479-484.
Elliott, M. C. and Stowe, B. B. 1978. Dyer's woad (Isatis tinctoria): from cultivated-to
cursed. Utah Science 39:87-89.
Farah, K. O., Tanaka, A. F., and West, N. E. 1988. Autecology and population
biology of dyers woad (Isatis tinctoria). Weed Science 36:186-193.
King, W. O. and Evans, J. O. 1983. Effects of several foliar applied herbicides on the
viability of dyers woad (Isatis tinctoria L.) seed. Proceedings of the Western Society of Weed Science 36:98-101.
Kropp, B. R., Albee, S., Flint, K. M., Zambino, P., Szabo, L., and Thomson, S. V.
1995. Early detection of systematic rust infections of dyers woad (Isatis tinctoria) using the polymerase chain reaction. Weed Science 43:467-472.
Kropp, B. R., Hansen, D., Flint, K. M., and Thomson, S. V. 1996. Artificial
inoculation and colonization of dyer's woad (Isatis tinctoria) by the systemic rust fungus Puccinia thlaspeos. Phytopathology 86:891-896.
Kropp, B. R., Hansen, D. R., Wolf, P. G., Flint, K. M., and Thomson, S. V. 1997.
A study on the phylogeny of the Dyer's woad rust fungus and other species of Puccinia from crucifers. Phytopathology 87:565-571.
Lovic, B. R., Dewey, S. A., Thomson, S. V., and Evans, J. O. 1988. Puccinia thlaspeos
a possible biocontrol agent for dyers woad. Proceedings of the Western Society of Weed Science 41:55-57.
Robbins, W. W., Bellue, M. K., and Ball, W. S. 1951. Weeds of California.
Sacramento: California State Department of Agriculture.
Roche, C. 1992. Dyers woad (Isatis tinctoria L.). Pacific Northwest Cooperative
Extension Publication 384:2 pp.
Varga, W. A. and Evans, J. O. 1975. Dyers woad and alfalfa interaction - a double take
of a competition study. Proceedings of the Western Society of Weed Science 28:38-39.
West, N. E. and Farah, K. O. 4-1989. Effects of clipping and sheep grazing on dyers
woad. Journal of Range Management 42:5-10.
Young, J. A. and Evans, R. A. 9-1977. Today's weed - dyer's woad. Weeds Today 9:21

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