Dyers Woad (Isatis tinctoria)

Status:

Listed Noxious Weed In Montana

History:

First Montana Specimen Collected 1

County:

Missoula

Year:

1934

“In the colonial United States, dyers woad was cultivated for dye-making properties. The source of the western establishment is traced to the early 1900’s as a contaminant in alfalfa seed from Ireland to a ranch in Siskiyou Co., CA, and as a contaminant in alfalfa seed in Utah. The first herbarium specimen from Utah is dated 1932, where it was found growing near the railroad. Early records indicate that dyers woad was reported from CA, ID, OR, MT, UT and WY.” (WWCB)

Habitat:

Biennial or perennial up to 3 ft. tall.  Spreads by seed.  Rosette formed 1^st year, flowering stem elongates 2^nd year.

Growth Habit:

Leaves:

Basal rosette leaves are long with short fine hairs. Stem leaves alternate, have short basal
lobes clasping the stem and without hair.

Stem:

Woody, upper portion is branched.

Flower:

Small, yellow, 4 petals 1/8 inch across.

Roots:

Heavy Tap root with lateral roots within the top foot of soil.

Seeds:

Plant has many, slightly pear-shaped, winged, black seedpods ½” long that hang like
ornaments. Each pod contains one seed. Each plant produces an average of
300 to 500 seeds but can produce as many as 10,000.

Other Notes:

"Dyer's Woad will establish along roadsides, gravel pits etc. From these easily established locations it can spread to grasslands, pastures, forests and croplands." (WWCB, 23)