University of Wyoming Extension News

Park County weed district asks rural residents to be on alert for Dyer’s woad

One Dyer’s woad plant was found recently along the North Fork of the Shoshone River, according to Sandra Frost, University of Wyoming Cooperative Extension Service educator in Park County.

Intensive searches upstream and downstream by employees of the Park County Weed and Pest Control District did not find more plants. District personnel ask that county residents be on the alert for this plant and report infestations to them, said Frost.

Cattle grazing capacity decreases on average 38 percent when Dyer’s woad infests Pacific Northwest rangeland, she said.

Dyer’s woad is a winter annual, biennial or short-lived perennial, 1 to 4 feet tall, that can move onto Park County cropland and rangeland very quickly. Originally from Russia, it is on the Wyoming noxious weed list, noted Frost.

Dyer’s woad is a member of the mustard family and has a thick taproot going down 5 feet. Plants will regenerate if top growth is removed. It is well-adapted to alkaline soils and arid climates.

Leaves up to 7 inches long form rosettes on the soil surface the first year. Leaf growth and rosette formation begin very early in spring to take advantage of spring moisture. The plant sends up stems and forms flowers in early spring of the second year. Stem leaves are bluish-green in color and have a prominent, cream-colored mid-rib extending the entire length of the leaf. Stem leaves have no petiole, clasp the stem and alternate along the stem.

Long, flattened seed pods dangle from the umbrella-shaped flower head. Seeds develop from green to black when mature.

Montana established the Montana Dyer’s Woad Cooperative Project in 1984 aimed at eradicating the weed from the state. At that time, 13 counties were infested with the plant. Intensive work has reduced the number of infested counties from 13 to four and the number of acres from 480 to 6.4, said Frost.

Find more information at “Ecology and Management of Dyer’s woad” at

For more information, contact Frost at (307) 754-8836 or

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