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Dyer's Woad (Brassicaceae (=Cruciferae), the mustard family
BACKGROUND: Dyer's woad was introduced into North America from Europe, probably late in the 17th century. It was cultivated as a source of blue dye and has since naturalized as a weed of dry areas in our region. Dyer's woad spreads primarily by seed.
DESCRIPTION: Dyer's woad can be a winter annual, biennial, or short-lived perennial. Basal leaves arise from thick taproot, are lightly pubescent, have long petioles, and are up to 8 inches long. Stem leaves clasp the stem and are lance shaped, not pubescent, and shorter than the lower leaves. Leaves all have prominent whitish midvein. Stems are up to 4 feet tall and bear 1/4-inch wide, yellow flowers in flat-topped clusters during May and June. Fruits are teardrop shaped, 3/4 inch long, purplish brown at maturity, pendulous, and each contains a single seed.
DISTRIBUTION: Dyer's woad is occasionally found in the eastern U.S., but is in the West where it is a serious weed. Dyer's woad is prevalent in central and many of the southern Idaho counties.
CONTROL: No biological control agents are available for dyer's woad, but herbicides are available.