The first few weeks of the growing season is a great time to police fields for suspicious weeds. Look for weeds that survived pre-seed burn-off or post-emergent sprays while others of the same species have died. These few weeds could be resistant, and it would be good to nab them early.
“It takes 14 to 21 days after a pre-seed glyphosate application for glyphosate-resistant kochia to become obvious, so keep an eye out while crossing over the farm while seeding or during in-crop herbicide applications,” said Angela Brackenreed, agronomy specialist with the Canola Council of Canada.
Kochia is far from the only herbicide-resistant weed to watch for. Weedscience.org reports 21 different weeds with herbicide resistance in the Canadian Prairies, many with Group 1 or Group 2 resistance and some resistant to multiple groups. Wild oats with stacked resistance were detected 20 years ago, and some have resistance to Groups 1, 2, 8 and 25.
Hugh Beckie, research scientist with Agriculture and Agri-Food Canada, estimates that herbicide-resistant weeds cost growers $1.1 billion to $1.5 billion per year.
“Without management, these weeds will continue to spread and the effect on grower profits will only get worse,” said Beckie.
He estimates that the number of acres on the Prairies with at least one resistant weed has gone from 10.9 million in the early 2000s to 38.0 million in 2014.