Weed of the Week: shepherd’s purse

Shepherd’s purse can have deleterious effects on farmers’ purses.

This fall annual should be all but killed for this crop year, but the steady moisture supplies and last year’s open fall means this hardy pest might be lingering in many prairie fields.

The weed was restricted to wetter spots and field edges before tillage was reduced in Western Canada.

Like its cousins narrow-leaved hawk’s beard, cleavers, flixweed and stinkweed, this member of the mustard family gets an early start in the spring and can quickly withstand removal efforts.

It is best controlled ahead of freeze-up with glyphosate or shallow, vertical tillage.

The weed is also known as shepherd’s pouch, St. James weed, pepper plant, mother’s heart, poor man’s parmacettie, sanguinary, shepherd’s heart and capsella.

It has developed resistance to Group 2 herbicides in Saskatchewan and Alberta.

Cotyledons are oval and have rounded tips when it is a seedling. The first leaves are lobed, and the leaves are covered in star-shaped hairs.

The immature plant’s leaf margins are highly variable, making identification tricky. They can be shallowly lobed or deeply cut.

The stems are sparsely branched and covered with star-shaped hairs. The stem leaves alternate. Balsal lobes of the leaves are pointed and clasp at the stem.

The weed grows up to 90 centimetres when not controlled and sprouts from a rosette at the ground. Mature plants have white flowers with four petals.

Flat pods form with a notched top and a small beak, and each contains about 20 seeds. Plants produce 45,000 seeds each if left to mature. It begins flowering early and continues to produce seed throughout the season, given the chance.

Seeds are orange, oblong and have a pitted surface.

Broadleaf herbicides are available that can control it in spring crops, but full rates and early treatment are needed to fully stop the pest.

Bromoxynil with MCPA and clopyralid with MCPA can be effective. Both work in cereals and flax, and there is a minor use label for Curtail (clopyralid) for canaryseed. As well, Buctril, Mextrol, Badge and Logic, bromoxynils, are also registered for canaryseed.

The weed can be a significant issue in non-herbicide tolerant broadleaf crops. In-crop applications of Odyssey and imazethapyr are effective in peas.

The weed is found in most areas of the Prairies with the highest populations in the canola belt.

However, fewer instances of shepherd’s purse are seen in the brown soil zone and Manitoba’s southern Interlake and Red River Valley regions.

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