If you’ve found herbicide-tolerant weeds in your field, you’re not in the minority.
Weed resistance is increasing worldwide, so it’s really important that Prairie growers understand growing herbicide tolerance, says one of the country’s top resistance experts.
“Group 2 really overshadows all the other groups in terms of weed resistance,” said Hugh Beckie, a research scientist with Agriculture and Agri-Food Canada, Saskatoon. “It’s remarkable considering this new chemistry was introduced in 1983, much later than some of the older herbicides.”
Rates of resistance have grown globally since 1950, with the grass families of weeds dominating all other groups, Beckie said during a session at FarmTech.
Canada ranks No. 3 in terms of global weed resistance (after the U.S. and France), with Western Canada and Eastern Canada having about the same number of resistant weeds. Group 1 resistance first appeared in Manitoba in 1990, and continues to be a problem in wild oats. Group 2 resistance has been found in cleavers in the Parkland region.
“In northeastern Saskatchewan, I would imagine that every pea field has Group 2 cleavers,” said Beckie. “It really is posing a challenge to pulse crop production, which is highly dependent on Group 2 chemistry.”
But increasingly, the problem is weeds with resistance to two or more groups. About 90 species of weeds have populations with multiple resistance, and that number is rising every year.
There have been cases of Group 2 and Group 1 resistance developing at the same time in wild oats, said Beckie.
Since there hasn’t been any new herbicide chemistry developed for more than 30 years, methods for combating resistance are few and shrinking.
Agriculture Canada has conducted surveys to find resistant varieties by randomly approaching farmers and scouting their fields. The Saskatchewan study was completed in 2015, Manitoba was surveyed last year, and it will be Alberta’s turn this year. Researchers will scout 250 to 300 fields pre- and post-harvest (with the latter focusing on glyphosate-resistant kochia and Russian thistle). Researchers expect they will find resistance in about half of the cultivated land surveyed.
“If you don’t have resistance yet, you’re in the minority. Don’t feel that you’re singled out. Most growers now have resistance,” said Beckie.
Randomly chosen growers will also be asked to fill out a survey on their weed management practices in order to find out which ones are more effective and what isn’t working.
More trouble ahead
The cost of managing resistant weeds is huge — an estimated $1 billion annually in Saskatchewan alone because of increased herbicide use and decreased yield and quality.
One of the ways growers are managing resistance is using two modes of action (glyphosate and one other) when growing canola. But the reliance on glyphosate is dangerous, said Beckie.
“In 2012, glyphosate usage was bigger than the next 12 combined,” he said. “It’s all about glyphosate now, or glyphosate mixtures, so we have to be careful about glyphosate selection pressures in particular. Glyphosate-resistant weeds worldwide are increasing.”
Glyphosate-resistant kochia is now established in Western Canada, and Russian thistle looks to be next — it’s in Montana and that’s why it’s a focus of the Alberta survey to be conducted this growing season.
In southern Alberta, resistant traits in kochia are outcrossing, and can be spread by the wind.
“If you have a glyphosate-resistant plant next to a non-resistant plant, there is about five to seven per cent outcrossing,” said Beckie. “It’s not great, but great enough. This is another way for resistance to spread.”
To deal with glyphosate resistance, growers of Roundup Ready and Liberty canola are now forced to use Group 4 herbicides, an older chemistry, because there is no other alternative.
Beckie advocates that growers keep careful records of cultural and management practices. This can include crop records, but should also include a record of which weeds appear in which field.
“That’s something we need records for,” he said. “If you don’t know how weed populations are changing, it’s hard to develop a program,” he said.
Using good sanitation methods will mean fewer resistant weeds. Other good practices include rotating herbicide use by group, scouting, and adopting diverse rotations.
“A lot of growers are being proactive and are using the practices we recommend, so I’m very optimistic,” said Beckie. “With lack of herbicide development, you have to use what you have and it’s a challenge. Be consistent and do the little things whenever you can and hope for the best from one year to the next.”