By Connor Lynch
GUELPH — Glyphosate survived the environmentalists but it looks like what was once called the holy grail of herbicides will succumb to nature’s boundless adaptability.
Glyphosate-resistant weeds, particularly Canada fleabane, have been appearing all over Ontario. In 2014, there was one field in Ontario with glyphosate-resistant Canada fleabane. In 2015, there were 40.
University of Guelph professor Peter Sikkema presented the research to farmers last month at the university’s Ridgetown campus.
Roundup Ready 2 Xtend, the new Monsanto soybean variety that’s resistant to a dicamba-based herbicide, a glyphosate alternative, was approved in time for this year’s growing season. There are already alternative herbicides to glyphosate available for corn.
An herbicide may be the most straightforward and impactful management tool but don’t rely solely on an herbicide for managing weeds, said OMAFRA weed management specialist Mike Cowbrough. Resistance is inevitable with any kind of pesticide. There are others ways to slow it down, he said.
“Fundamentally, it’s a numbers game,” when it comes to resistance. Start with the weed that’s most abundant in your fields; just by the numbers it has the best chance of developing resistance. For those species, multiple avenues of attack are necessary.
That means basic agronomy, he said. Planting competitive crops (broadleaf plants tend to be more competitive, he added), maintaining soil fertility, keeping up with crop rotation, and practicing good tillage will help keep the weeds down.
Finally, cover crops will keep light from getting to the seeds of early blooming weeds like Canada fleabane, he said. “If you’re in a corn and soybean rotation, why not put in oats after the soys are out?”
