Woad or glastum
Dyer’s woad is a distinctive plant that is in the mustard family and can be a winter annual, a biennial or a short-lived perennial. This plant can grow up to 4 feet tall and has bluish-green leaves covered with fine hairs. The leaves alternate with a prominent cream colored mid-vein and are especially noticeable on the rosettes. When this plant bolts, it can produce up to 20 stems, and it grows and sets seeds very quickly. It flowers from May to August just depending on the climate and this plant is very similar in appearance to the common mustard flowers. The flowers are found in clusters at the end of the branch tips and when flowers go to seed, the large blackish-blue seed pods are very distinguishable. This plant spreads primarily by seed and has a taproot that can reach up to 5 feet in depth.
The key identifying characteristic of Dyer's woad is the ark seed pod at the seed set. Areas infested with Dyer's woad resemble areas affected by wildfire due to these dark pods.
Dyer’s woad prefers dry, rocky soils common to hill sides. This plant can also be found in rocky and sandy soils with very availability to water. It is found in dry pastures, uncultivated fields, right-of-ways, waste areas, forests and rangelands.
There are herbicides and other control methods that commonly Dyer’s woad. Hand pulling or digging has shown to be the most effective option, done before flower and seed establishment. For more information on control methods contact the Weed and Pest office.
The use of Dyer’s woad dates back to ancient times when Romans stained their body with the plant. It was introduced into North America during the colonial period and was used before indigo dye was available. It then spread, through contaminated alfalfa seed shipments to the West, where it has become a nuisance in range, croplands and forest.