Weed of the Week: wild mustard

Wild mustard remains an elusive foe in Western Canada, despite all the great tools for controlling broadleaf weeds.

It remains one of the pests that producers struggle with every year.

The weed can condemn a canola crop to the sample reject bin if more than five percent is found. It is also a threat to tame mustard growers.

All mustard types, especially the oriental and brown, should be planted in fields that are known to be relatively free of wild mustard. The weed might be separated mechanically from yellow mustard with its large seed, but that isn’t possible with the brown and oriental types.

Known to biologists as Sinapis arvensis or Brassica kaber, it is controllable in herbicide tolerant canola but creates problems for Polish canola and non-HT varieties because of its shared brassica heritage.

For a good portion of the last century, western Canadian wheat crops often had a yellow phase in late June or early July when wild mustard came through the crop and flowered.

It would last a week or two and the wheat would grow through the pest, although not without a yield penalty.

The aggressive plant can be found in most of the grain growing regions of the northern hemisphere.

It can be short or tall, reaching up to 100 centimetres in some cases. It has branches and leaves that are hairy, unevenly toothed and end in a rounded lobe.

Unlike canola, wild mustard’s leaves are supported by short stalks.

Branches at their base often have violet spots. The stem hairs are stiff and pointed toward the ground.

Seeds begin germination when soil temperatures reach 2 to 4 C and will continue with fresh rain and as the soil temperature rises.

Seeds prefer to start shallow in the soil but can hang around for up to a decade until conditions are right for it to germinate.

Wild mustard produces up to 3,500 seeds per plant. The seeds vary from brown to black and have a gelatinous coating after they are soaked in water for a few minutes. Dry conditions early in the season will limit populations, such as this season in much of Western Canada.

Seeds can survive animal feeding, which means hay from fields where mature plants are present can help spread the weed.

Farmers who scout for the weed early in the season should look for broad, kidney-shaped, cotyledon leaves.

The yellow flowers can be mistaken for other mustard family plants. The seedpods are also known as siliques.

It differs from other mustards by having some seeds in the flat terminal end of the seed pod.

The pods narrow toward the last third of the terminal end and are held to the plant at the other end by a short, thick piece of stalk.

The weed discourages many producers from growing mustard because of its ability to contaminate fields of tame mustard.

Wild mustard plants act as hosts to disease-causing organisms, which can damage tame brassicas, such as canola. It can activate spores and become infected by disease when growing in soil containing clubroot.

Ten plants per sq. metre in cereals can result in a 10 to 20 bushel per acre yield loss, while 10 plants per sq. metre in flax can cut yields by up to 50 percent and 33 plants per sq. metre can reduce yields by 65 percent in peas.

The good news is that a variety of herbicides are available to control the weed in a pre-seed burnoff and in-crop situations. The only control challenges are in non-herbicide resistant brassica crops and when the weed’s growth stage is well advanced before application.

Mustard plants can be controlled with herbicides such as 2,4-D, Banvel, bromoxynil, MCPA, glyphosate and most ALS herbicides, including imidazolinone and sulfonylurea.

Some of the weed’s population has developed tolerance to Group 2, ALS inhibitor herbicides, including ethametsulfuron-methyl, imazethapyr, thifensulfuron-methyl and tribenuron-methyl.

The most effective controls are multiple mode of action approaches, crop rotation and limiting seed production. Control in pulse crops can be difficult, outside of Clearfield lentil options. Odyssey can be used effectively in peas.

Weed wipers and wicks loaded with glyphosate can control the pest as it grows through shorter pulse crops.

The spring annual has little or no resistance to tillage, but tillage can also disturb ungerminated seeds, causing a new crop of problems and creating moisture loss, erosion and increased production expense.

Look-alike weeds are its cousins tumble mustard (Sisymbrium altissimum) and wild radish (Raphanus raphanistrum).

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