Description: Winter annual, biennial, or short-lived perennial 1 to 4 feet. The large tap root may exceed 5 feet in depth, and can sprout new plant if the original plant is severed. Leaves bluish green, alternate and basal, with a whitish nerve on the upper surface of the blade. Flowers yellow, small, and crowded into flat-topped clusters. Purplish-brown seed pods containing a single seed appear near mid-summer giving this weed a totally different appearance from the other mustards.
Habitat: Native to Europe. Infests rangelands, grain fields, pastures, alfalfa, waste areas, roadsides, railroad right-of-ways, and fencelines. Extensive root system contains large nutrient reserves which make this weed difficult to control. Contaminated hay is one of the major causes of this weed's expansion.
Distribution: Large infestation of Dyer's Woad are found from Scott Valley (Siskiyou County) to Tulelake (Siskiyou County and Modoc County), New Pine Creek, Davis Creek, and Adin (Modoc County). Scattered or single plants can be found throughout northern California.
Flowering Period: April to June.