Weed of the week: Stinkweed

Stinkweed isn’t the worst of the weeds that are common on the Prairies, but little by little it eats away at crop resources and selects itself for herbicide avoidance.

It is fairly easy to kill with the right herbicides applied at the right time, but by the time farmers get the chance it has already sucked up a fist-full of nutrient dollars.

As well, the winter annual will germinate from seed mid-season, after crops have passed most herbicide windows.

Stinkweed can withstand hard frosts in the spring and midseason droughts and still manage to produce up to 15,000 seeds in a single year.

All those seeds make it a danger to developing resistance, and it has, making Group 2 controls unreliable when dealing with this old problem.

Stinkweed can withstand hard frosts in the spring and midseason droughts and still manage to produce up to 15,000 seeds in a single year. | File photo

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The seeds are even tougher than the plants, with heavy seed coats that can remain viable in the soil for up to seven years. Seeds that are incorporated into the soil profile below the cropping region can last 20 years or more.

The plants grow up to 60 centimetres high and are often branched. They are typically shorter, but by the second week of May the weed can be more than 30 cm tall and difficult to kill.

Lower leaves can be in the form of a rosette. Leaves are alternate and without hairs. The upper leaves clasp at the stem.

The small, white flowers are stalked, with yellow to green centres. Seeds are held in tan packets.

Stinkweed, formally known as thlaspi arvense, is also called Frenchweed, pennygrass and fanweed.

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Not only is it a pest on its own, but it also acts as host to other pests, including clubroot and the tarnished plant bug.

The weed can also taint milk and meat with bad flavours and contains enough glucosinolates to be toxic to livestock.

During periods of drought, such as the late 1980s, researchers in Western Canada documented cattle abortions, animals off feed and even death from eating the weed.

The best time to deal with the pest is in the fall ahead of freeze up. Fall herbicide burn-off strategies tend to be successful.

Bromoxynil with 2,4-D or MCPA are effective at controlling the weed in the appropriate crops. Most Group 2 chemistries are also effective, but the weed has developed resistance to Group 2 herbicides in parts of Alberta.

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Glyphosate, glufosinate and Clearfield products provide control in herbicide tolerant crops. Tillage can control the weed, but it will survive if not fully uprooted or chopped.