One Dyer's woad weed does not an infestation make, but the recent find of a single plant of the invasive species in Wyoming's Park County has triggered a request to be on the lookout for the fast-spreading threat elsewhere.

Found along the Shoshone River, the  single find brings to mind the situation several years ago in Utah when weed scientists reported a small patch of the woad was reported. Neglecting to address the issue quickly, Dyer's woad is now a highly invasive species in Utah.

Intensive searches upstream and downstream on the Wyoming river by Park County Weed and Pest Control District workers did not find more plants. District personnel ask that county residents be on the alert  for the plant and report infestations to them, says Sandra Frost, University of Wyoming Cooperative Extension Service Park County  educator.

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

The weed is a member of the mustard family which has a thick taproot going down five feet.  Plants will regenerate if top growth is removed. It is well adapted to alkaline soils and arid climates.

Leaves up to seven inches long form rosettes on the soil surface during the first year of growth. Leaf growth and rosette formation begin very early in the spring to take advantage of 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 stem. 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 about 6.5, Frost reports.

For more information on Dyer's woad, see Ecology and Management of Dyers Woad" at www.mt.nrcs.usda.gov/technical/ecs/invasive/technotes/, or call Frost at  (307) 754-8836. She may also be contacted by e-mail at [email protected].