Dyers woad (Isatis tinctoria L.)
Dyer’s woad was originally cultivated as a source of blue dye and has since become invasive in many western states. It is allelopathic, meaning it produces chemicals that inhibit the growth of nearby plants, allowing it to dominate disturbed sites and rangelands.
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Dyer’s woad is a biennial or short-lived perennial forb that grows from a deep taproot. In its first year, it forms a basal rosette of elongated, teardrop-shaped leaves with a distinctive white midvein (often described as a “white spine”). Basal leaves may have fine hairs.
In subsequent years, the plant produces erect flowering stems that typically reach 1–4 feet tall. Stems are frequently branched near the top. Stem leaves are alternate, bluish-green, hairless, and have lobed bases that clasp the stem. All leaves display the prominent white midvein that aids in identification.
Flowering occurs from late spring to early summer. Small, bright yellow flowers (about â…› inch across) are borne in branching panicles at the ends of stems. Each flower has four petals, characteristic of the mustard family.
Seeds are highly distinctive and serve as a key identification feature. They are produced in ½-inch-long, pear-shaped pods that are black and winged. The pods droop from the branches as they mature.
Quick ID Guide
Life Cycle:
• Biennial or short-lived perennial
• First-year rosette
• Second-year flowering stem
Height:
• 1–4 feet tall
Stems:
• Erect
• Branched near the top
Leaves:
• Bluish-green
• Alternate
• Prominent white midvein
• Upper leaves clasp the stem
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Flowers (Late Spring–Early Summer):
• Bright yellow
• Four petals
• Small (~â…› inch)
• Arranged in panicles
Seeds:
• ½ inch long
• Pear-shaped
• Black and winged
• Drooping pods
Management Options
Prevention and cultural control strategies should be emphasized whenever possible. There are currently no approved biological control agents for dyer’s woad, though research and trials are ongoing.
Because dyer’s woad has a taproot, small infestations can be effectively managed by hand pulling or digging, ensuring the entire root is removed. Plants are easiest to control in the rosette stage.
Controlled grazing by goats early in the growing season can significantly reduce or eliminate populations. Repeated mowing after bolting and before seed production can prevent seed development. Mowing approximately two weeks after an herbicide application can improve root kill and prevent seed production. Do not mow once seeds are present.
Large infestations may require herbicide treatment. Spring applications targeting rosettes or early bolting plants are recommended for best results. Always read and follow herbicide label directions before application. Contact Sublette County Weed & Pest for assistance with product selection, rates, and timing.
