War on Weeds: Dyers woad

Richard Old


This weed may invade your land. Be ready to oppose it.

The Enemy: Dyers woad (Isatis tinctoria L.)

Strategy: This biennial plant was introduced into the U.S. in colonial times. It was brought here as a blue dye. This mustard is one that is shows its beautiful, bright-yellow bloom in mid-May to early June. It has inhabited thousands of acres near Pocatello and south as it is one of the worst weeds there. The plant has thick, light-green leaves with a noticeable white midvein in its first year and then sends up three to seven stalks that produce flowers at the top in an umbrella fashion. The seeds can last up to 10 years in the soil.

Attack: Dyers woad germinates late in the fall to early spring and gets established before many other plants. Its rosettes spread out nearly 12 inches and it will grow to about 4 feet tall. It produces dark purple to black-looking seeds that hang from the top, which allows the seeds to spread long distances and keeps the seed viable in the soil for many years. The plant produces a tough taproot.

Defense: As this is a biennial plant, mechanical control can be effective. In fact, many counties have a “Bag-O-Woad” program in which they will pay for garbage bags full of this weed. Herbicides such as Telar XP, Escort XP and Chaparral/Opensight are most effective if applied in the late fall and during the active growth of the weed. There are currently no biocontrols available for this weed and most animals will not eat it. This canola-looking plant is found in most counties, so if you suspect you have seen it, let your county weed superintendent know so that it does not become a serious problem.

To learn more, call Bonneville County Weed Superintendent Jeffrey Pettingill at 208-529-1397 or email weeds@co.bonneville.id.us.