Growers are getting mixed messages on glyphosate resistance from two rival chemical companies.
Monsanto Canada says farmers shouldn’t get too wound up about the subject, while Syngenta is preaching extreme caution.
Faced with erroneous reports of resistance and growing producer concerns that their reliance on glyphosate will lead to the development of a superweed, Monsanto felt it was time to respond.
In an Aug. 9 News release
news the company tried to assuage mounting fears about resistance.
“We want growers to fully understand that use of Roundup brand herbicides in Roundup Ready canola, grown in crop rotation, does not significantly change the risk of glyphosate resistant weeds occurring in Western Canada,” said Rob Neyedley, Monsanto’s technology manager of chemistry and Roundup Ready crops.
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Contrary to an advertisement published by Bayer CropScience last fall claiming resistance had been identified in Canada fleabane, further lab testing confirmed the case did not meet the criteria.
So after more than 30 years of using the herbicide, there are still no confirmed cases of glyphosate resistant weed species in Canada.
Neyedley said he doesn’t want growers to overreact and shy away from using Roundup Ready crops or Roundup herbicide for fear of developing weed resistance.
“Don’t get overly concerned,” he said.
That is at odds with what Syngenta is telling farmers. Chuck Foresman, the company’s manager of weed resistance strategies, said the threat is real. Scientists have identified five weed species resistant to the herbicide in the United States.
Foresman recently toured a cotton field that had a serious post-emergence weed problem.
“It was just an immense population of palmer pigweed that walked right through very high rates of glyphosate,” he said.
Down the road, resistance could develop in a weed that farmers can only control by hand-picking or cultivation, which is why Foresman believes it is dangerous to downplay the issue.
He said three million acres of cropland in the U.S. are already infected with glyphosate resistant horseweed.
“If you’re a grower and you happen to have one of those acres or 1,000 of those acres, you’re not going to be convinced that (resistance) is rare,” said Foresman.
But Neyedley said a website developed with the assistance of weed scientists in more than 80 countries, at www.weedscience.org, shows the incidence of weed resistance to glyphosate is much lower than it is for Group 1 and Group 2 herbicides.
Five glyphosate resistant weed species have been identified in North America, all of which are in the U.S., compared to 19 in the Group 1 and 55 in the Group 2 categories.
“Glyphosate is actually a low risk herbicide for developing weed resistance,” said Neyedley.
By contrast, one in six fields in Western Canada has Group 1 or Group 2 wild oat resistance problems. Green foxtail resistant to Group 1 products can be found in all three prairie provinces. Broadleaf weeds like chickweed and kochia have demonstrated resistance to some common Group 2 products.
Neyedley said he can’t understand why Syngenta devotes so much energy to informing growers about glyphosate resistance rather than telling them how to manage the resistance problem that has already emerged with the Group 1 and 2 chemicals it sells.
“I get a little confused personally with their (message) on resistance,” he said.
Foresman said it is only a matter of time before glyphosate resistance becomes more prevalent due to the popularity of the chemical.
In the U.S., there are 200 million acres treated with glyphosate, 85 percent of which receives no other herbicide treatment.
“The complete burden for weed control is on glyphosate so the selection pressure is absolutely huge,” he said.
In a website devoted to the issue, www.resistancefighter.com, Syngenta is promoting its 2-1-2 approach to weed control to help combat what it feels is a looming threat to growers. It says there should be no more than two applications of glyphosate on one field over a two-year period.
The program calls for the use of a variety of other herbicides on Roundup Ready crops.
But Neyedley said growers can use glyphosate at multiple times throughout the year in preseed, in-crop and preharvest situations.
“These applications target different weed species and populations, which minimizes overall selection pressure for glyphosate resistance.”
Neyedley said growers shouldn’t disregard the threat of glyphosate resistance.
But as long as they use the right herbicide at the recommended rate at the correct time in weed development, they will minimize the risk of that happening soon.
If resistance does occur, there are methods for handling the problem, as demonstrated in the U.S., he said.
