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Idaho Enterprise

War on Weeds—weeds are everybody’s problem

Photo courtesy of Steve Dewey, Utah State University, Bugwood.org

THE ISSUE:  Dyer's woad 

 Dyer’s woad (Isatis tinctoria) is a biennial or short-lived perennial that is native to Europe. It was originally introduced into the U.S. as a source for making blue dye and for medicinal purposes.  It invades rights-of-way, rangelands, pastures, cropland, and other disturbed sites.  Its presence reduces forage and crop production. It has become a widespread problem especially in southeast Idaho. 

Dyer’s woad seedlings can establish in the spring or the fall. Seedlings that establish in the fall overwinter as rosettes and then bolt in the spring. Seedlings that establish in the spring will remain in the rosette stage until the following spring. After bolting dyer’s woad can grow up to 4 ft. tall. Its leaves are lance shaped, 1-7 inches long, bluish green in color, with a whitish midvein and slightly wavey margins.  It has distinct yellow, flat topped, clusters of flowers. Each flower has 4 petals. Seeds are housed inside brown-black oblong pods, each pod contains a single seed. A single plant can produce 85–500 seeds in a single year. Seeds can be transported easily on animals, clothing, and equipment. Dyer’s woad has a taproot that can be up to 1½ feet long. 

Integrated Pest Management (IPM) Options: 

• Prevention— Learn to identify this plant. Clean equipment after leaving an infested area. Do not transport unknown plant material. 

• Mechanical— Hand digging individual plants can be an effective method of control. Spring tillage and mowing prior to the production of seed can also be effective forms of control. 

• Cultural— Establish a healthy stand of beneficial plants that will compete with Dyer’s Woad. 

• Chemical— 2,4-D LV ester, aminocyclopyrachlor + chlorsulfuron (Perspective), chrlorsulfuron (Telar), imazapic (Plateau), metsulfuron (Escort and others) are herbicide active ingredients that can effectively control Dyer’s Woad. Always read and follow herbicide label directions! 

Justin Hatch, University of Idaho Extension Agriculture Educator in Caribou and Bear Lake Counties. 208-547-3205
[email protected]

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