ST. JEAN BAPTISTE, Man. — The top 10 list of weeds in Manitoba has undergone radical changes in the last 20 years.
Green foxtail remains the biggest crop pest, but barnyard grass, volunteer canola and yellow foxtail have joined it in the upper rankings of most-seen weeds, rising from relative obscurity in 1997.
But for every rise there must be a fall, and formerly vexatious weeds, such as Canada thistle, redroot pigweed and wild mustard, have fallen down the rankings.
Quackgrass, once a great menace, has fallen from 10th to 38th place.
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“These are big shifts,” Ingrid Kristjanson, a Manitoba Agriculture crop production adviser in Morris, said during St Jean Farm Days, held Jan. 4-5.
Every 10 years, Manitoba Agriculture surveys fields to see what is growing within crops. Results are affected by moisture, variable growing conditions and random occurrences inherent in any test, so the list won’t hold true for every field in every situation.
However, real changes are being seen.
Volunteer canola is widespread now, following heavy rotations and shifts in herbicide use, while wild oats and Canada thistle have also been affected by products and practices.
Dandelions were only the 20th most common weed in 1997, but today are up to seventh.
Each crop has its own list of problem weeds, with today’s spring wheat facing (in order of severity) green foxtail, wild buckwheat, wild oats and volunteer canola. Oats confront green foxtail, barnyard grass, yellow foxtail and wild buckwheat. Canola struggles with green foxtail, wild buckwheat, volunteer wheat and yellow foxtail.
Soybeans combat volunteer canola, wild buckwheat, barnyard grass and dandelions.
The biggest gainer among the weeds has been biennial wormwood, which now functions as an annual, Kristjanson said. It moved 30 places higher on the list.
Glyphosate has helped hammer down some old problems like quackgrass, but could eventually create another group of rising problems as resistance spreads.
“Be on the lookout for oddball things,” said Kristjanson.
