There are advantages in the Canadian environment that should help farmers and the industry avoid fungicide resistance problems, but vigilance is still needed.
Bayer recently brought its leaders from across North America in its fungicide business to Guelph for a summit and invited local agronomists, researchers and crop pathologists.
Why it matters
Fungicides are important to controlling diseases in crops, and in most cases in row crops, haven’t seen resistance grow like herbicide resistance has in weeds.
Bayer’s top expert on fungicide resistance, Andreas Mehl, covered the efficacy and trends for fungicide resistance around the world, including North America. Compared to the significant selection pressure on fungicides in Europe due to climate and more intense use, he sees few risks in row crops in North America for fungicide resistance.
Albert Tenuta, OMAFA’s field crop pathologist, differentiated between the realities of fungicide resistance in field crops versus horticulture and greenhouse crops.
In horticulture, ornamental and greenhouse crops fungicide resistance “is a real issue here and one that we have to take seriously.”
However, there are fewer risks of fungicide resistance in field crops, compared to the significant challenge that is herbicide resistance, which is growing.
Weeds show up every year. Pathogens don’t
Think of when weeds start, said Tenuta. They start growing at the same time as the crop, so there’s a constant need to manage them.
“It starts the day the seed’s planted and goes to the day it’s harvested,” he said.
“Those weeds are present for the year every year, and those continue to build a lot of selection pressure for herbicide resistance.”
Fungicides target pathogens, which vary by environmental conditions and some years might not even be present.
“So the frequency and the scale of what we’re trying to target or control is different.”
That means less selection pressure for fungicide resistance in field crops in most of Canada.
Where resistance has already taken hold
An exception is a strobilurin (a quinone outside inhibitor or QoI fungicide) resistance challenge for Ascochyta blight in chickpeas in Western Canada, which has been a problem for more than 20 years.
“I would definitely not recommend QoI use in chickpeas anymore,” said Mehl. Indeed, he said the use of strobilurin fungicides is mostly over in Europe because of resistance.
There are resistance problems in Europe where the climate is wetter, and farmers aggressively chase higher yields in crops like cereals.
There are also smaller fields, said Mehl and when that is combined with racing to get high yields, “you can only achieve it with much more higher intensity, more fertilizers, partly irrigation and also a lot of fungicide use.”
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On Ireland’s high-humidity climate “So they spray, and they spray and they spray.” Andreas Mehl, Bayer fungicide resistance lead |
Ireland is a smaller country with high humidity, “so they spray, and they spray and they spray,” he said. The resistant spores then float across to England, which doesn’t make farmers there very happy.
The British then have to spray fungicides three or four times per year. And then resistant spores end up in France.
“We see a gradient of resistance from the northwest to the southeast,” said Mehl.
French farmers are also reducing rates of product application, even to one third the label rate, with pressure to use fewer pesticides and save money, he says, which plays right into the development of resistance. That means the worst resistance problems in Europe are in France.
Why the math is different in North America
Compared to that problem, North American fungicide resistance in row crops is far less of an issue.
Mehl said that in Canada, with larger acreages than in Europe, there isn’t as much of a need to drive yields on every acre. In Ontario, that is changing as land grows in value and farmers manage new pests like tar spot while continuing to push wheat yields with higher management, including with fungicides.
The discussion is different in horticulture, fruit and vegetable and greenhouse crops, however, and Bayer held a second day of meetings just on those crops.
“A cut flower grower in Ecuador, some spray up to 100 times per year in the greenhouse. This is how to build resistance,” said Mehl.
Resistance doesn’t build in a single season
A misconception is that fungicide resistance develops in a year, said Gursahib Singh, field crop pathologist at the University of Guelph’s Ridgetown campus.
Resistance takes years of spraying a fungicide. Fungal pathogen populations are dynamic, and it takes time to select for resistance.
He also warned against just switching brands to try to manage resistance. Make sure that it’s a switch of mode of action. And be careful, as many products are mixes of multiple active ingredients.
Tenuta suggested that farmers who think a fungicide failure is because of resistance should make sure to investigate all the other reasons the fungicide might not have worked.
“It has to be an extreme case to get to that point,” he said.
Before you blame resistance
- Resistance takes years of repeat applications. It does not appear in a single season.
- Fungal pathogen populations are dynamic, and selection for resistance takes time to show up.
- Switching brands is not switching chemistry. Confirm the mode of action actually changes.
- Many products carry more than one active ingredient. Read the full mix before assuming a rotation.
- Rule out every other reason a spray underperformed first. Tenuta says it takes an extreme case to land on resistance.
While the risks are there, Mehl said an application of fungicide in a crop that needs it one growing season doesn’t create selection pressure for resistance. He said he’s not worried about resistance in the main cereals and corn crops in North America.
Vigilance and good stewardship, however, remain necessary.
“When it comes to fungicide resistance, it is real for Ontario,” said Tenuta.
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