In early May, pale yellow carpets some hillsides of Northern Utah. The plants are a non-native known as Dyer’s Woad. This Asian member of the cabbage family has been cultivated as a dye and medicinal plant in Europe and Asia for 2000 years. Dyer’s Woad produces a glorious blue dye, but the process is tricky. No synthetic dye equals the color and characteristics of woad dyes.
Woad had arrived in Utah by 1932 as a seed contaminant. Now it is a noxious weed. Woad has a number of unique abilities that contribute to its vigor. Being a biennial plant, it spends the first year of life as a rosette of leaves, building reserves. In its second year, those reserves allow a woad plant to send forth a tall, lanky stem covered with pale yellow flowers that ultimately yield up to 10,000 seeds per plant.
Although Dyer’s Woad is not toxic, few animals relish it either. The seeds have chemicals that inhibit germination and root elongation in other plants, giving woad a competitive edge. Woad causes millions of dollars in losses each year, so control is a major issue. Herbicides and mechanical removal are best used against the rosettes, but nature has provided a native fungus that views woad as dinner. This rust fungus is very effective at eliminating or severely reducing seed production. Plants infected with the rust fungus are misshapen, wrinkly, and covered in dark spots. Those spots brim with rust spores. Therefore, when removing woad, leave the sickly plants to infect yet more woads.
This is Linda Kervin for Bridgerland Audubon Society.
Photos: Brad Krupp, Utah State University, Bugwood.org
Text: Michael Piep, Utah Native Plant Society
Intermountain Herbarium: https://herbarium.usu.edu/
Washington Weed Board: https://www.nwcb.wa.gov/weed_info/Written_findings
Edmonds, J. 2006. The History of Woad and the Medieval Woad Vat. https://www.lulu.com/product/paperback/the-history-of-woad-and-the-medieval-woad-vat/4928037
Shaw, R.J. 1989. Vascular Plants of Northern Utah. Utah State University Press, Logan, Utah. https://www.usu.edu/usupress/books/index.cfm?isbn=1417
Welsh, S.L., N D. Atwood, S Goodrich & L.C. Higgins. 2008. A Utah Flora, 4th Ed. Brigham Young University, Provo, Utah. https://www.amazon.com/Utah-Flora-Stanley-L-Welsh/dp/0842525564