Weed of the Week: flixweed

Flixweed is well known to farmers of the southwestern Prairies and the U.S. Plains as a stubborn pest wherever soil is lighter or traditionally drier.

Also known as tansy mustard, this brassica has remained a problem since the days of tillage summer fallow.

Its persistence and yellow flowers likely gave it the tansy name, derived from athanaton, the Greek word for immortal.

It is not related to the sunflower family’s common tansy, also a prairie weed.

The plant is considered safe for some herbal uses, but it can poison livestock when animals feed on it exclusively over longer periods.

The weed can be an annual, a winter annual or a biennial. It reproduces exclusively by seed.

The plant reaches up to a metre in height when left undisturbed, and the feathery, finely dissected leaves alternate up the stem, leaving a different impression from other mustards and rapeseed plants.

However, the pest has the familiar taproot that makes it tough to beat should it escape early control.

Flixweed has two true tansy-mustard cousins, but they are shorter with heavier stalks.

Flixweed’s leaves are covered in tiny hairs, and can vary from green to grey. Small mustard-type flowers appear in late spring or early summer and vary from yellow to nearly white.

The plant gives off a musty smell, especially when mowed or when the stalks or leaves are bruised. Leaves are bitter tasting.

Unlike most other mustards, flixweed has narrow cotyledons with stalks. The initial set of leaves is three-lobed and hairy.

Seedlings appear in a cross configuration, but the rounder leaves quickly give way to the plant’s characteristic fern-like leaves.

Seeds are located in mustard-like seed pods and are oblong and orange in colour. The plant is a large seed producer.

Germination can take place all season, but most start life in the fall, creating small rosettes that wait for spring to get a head start on the crop.

The weed provides an early season home for flea beetles.

Control is best accomplished with post harvest spraying and spring burn off. Spring tillage is an option.

A variety of in-crop control options are available.

Bromoxynil with MCPA (Buctril M) and clopyralid with MCPA (Curtail M) are effective in cereals and flax.

Group 2 products such as thifensulfuron with tribenuron (Refine) will kill it, along with a variety of other broadleaf herbicides.

In peas, imazamox and imazethapyr (Odyssey) or MCPA ammine can be used.

Clearfield products are effective against the pest.

Ethametsulfron (Muster Toss-N-Go) can be used in non-herbicide tolerant canola and sunflowers and brown and oriental mustard.

Canaryseed can use Buctril M, Curtail M, dicamba with MCPA and/or mecoprop, fluroxypyr with clopyralid and MCPA (Prestige XC) and fluroxypyr with MCPA (Trophy).

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