Invasive Species of the Month: July 2012
Dyer's woad (Isatis tinctoria)
Dyer's woad is a biennial and sometimes winter annual or short-lived perennial herb that was introduced from Europe and Asia for use as a blue dye. It can form dense infestations that displace native forage species and degrade wildlife habitat. Dyer's woad reproduces primarily by seed and has thick taproots that penetrate the soil to an average depth of 3.5–5 feet.
In its first year, the plant exists as a rosette. Woody, flowering stems appear in the second year and are heavily branched toward the top of the plant, which can grow 1–4 feet tall.
Rosette leaves are hairy, bluish-green, and 1.5–7 inches long. Upon maturity, the plant produces alternate, oblong to lanceolate, bluish-green leaves that clasp the stem. Leaves have a prominent cream colored midrib and are up to 8 inches long.
Small, bright yellow, 4-petal flowers are 0.25 inches wide and occur in flat-topped or umbrella-shaped clusters on the stem tips. Flowering occurs from spring through late summer.
Seeds and Fruit
Seedpods are dark brown to black, teardrop-shaped, flattened, and hang from small stalks at the stem ends. Each pod contains a single oblong seed.
Dyer's woad can be found in areas with dry, rocky, or sandy soils, such as pastures, fields, rangelands, grasslands, and along roadsides.
Species Identification and CharacteristicsAlberta Invasive Plants Council Fact Sheet (PDF)
Colorado Department of Agriculture Fact Sheet (PDF)
Invasive.org Images and Overview
Montana Weed Control Association Fact Sheet