Dyer's Woad (Isatis tinctoria) is an herb associated with the mustard family. I. tinctoria's origins date back over 2000 years. In Europe, this plant has been cultivated as a source of blue dye and for medicinal properties since the 13th century. Within the last century it has become a serious problem on rangelands and in cropland of the United States (Young and Evans 1971, Varga and Evans 1978). This plant, as found in Utah, is a winter annual, biennial, or a short lived perennial. The leaves are alternate, simple, petiolate, bluish-green with a whitish vein on the upper surface of the blade.
The flower has a flat top with yellow petals. The fruit is a purplish-brown pod containing one seed. Dyer's Woad has a thick tap root that can exceed 5 feet in depth. Shown above is a fence post tall Dyer's Woad plant along Hwy 89 in the northern part of Weber County.
This invader is found mostly in disturbed sites, such as range, cropland, dry areas, woodlands, and pasture sites. This a major problem because Dyers Woad overtakes native grass, and most livestock and wildlife don't graze it. Shown below is the typical habitat of our local Dyer's Woad - foothills that rise up to the east. This scene from a development near the Weber and Box Elder County lines shows how Dyer's Woad will take over when land has been cleared for development and then left alone for a time. Dyer's Woad is spread from place to place by seed, which become viable comparatively early during seed production. Fortunately, other than the sheer number of acres infested with this particular weed, it is rather benign compared to some of the other noxious weeds found in the county.
When Dyer's Woad is found in the middle of incorporated cities and no attempt is made to control the infestation, the environmental impact on both private gardens and public recreation can be severe. This recent photo (below) is taken from the Weber County Fairgrounds and shows Dyer's Woad inhabiting the Browning Army Reserve Center, which borders both Weber County and the City of Harrisville.
Integrated Control methods are the most cost effective way to attack an infestation of I. tinctoria
in the majority of its settings. There are very good herbicides for treating Dyer's Woad in non-crop and rights of way environments. In croplands, good solid farming methods usually render this weed harmless. Orchards and vineyards make the worst cleanup challenge when Woad invades. In Northern Utah, many thousands of acres of Dyer's Woad inhabit our hillsides and valleys. Biological controls are the only practical hope for slowing the spread of what has already gotten quite a foothold here.