Idaho OnePlan recommends the website of the Idaho Weed Awareness Campaign as the best resource for up-to-date information about Idaho's noxious weeds, and their control.
Source for this page: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller

BACKGROUND

Dyer's woad (Isatis tinctoria) was introduced into North America from Europe, probably late in the 17th century. It was cultivated as a sources of blue dye and has since naturalized as a weed of dry areas in our region. Dyer's Woad spreads primarily by seed.

(Thumbnail images are linked to a larger photo)

DESCRIPTION

Dyer's woad can be a winter annualPlant that germinates, flowers, seeds, and dies during one growing season, biennialPlant that germinates in one growing season, then flowers, seeds, and dies during a second, or short-lived perennialPlant that lives for more than 2 growing seasons. BasalAt the base of plant or plant part leaves arise from a thick taprootA thick, central root with minimal branching, are lightly pubescentThe hairs on a leaf, stem, or flower, have long petiolesleaf stalks, and are up to 8 inches long. Stem leaves claspLeaves that appear to wrap around the stem at their base the stem and are lance shaped, not pubescent, and shorter than the lower leaves. Leaves all have a prominent whitish midveinThe center and usually most prominent vein on a leaf. Stems are up to 4 feet tall and bear -inch wide, yellow flowers in flat-topped clusters during May and June. Fruits are teardrop shaped, -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 it 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.