Southern Manitoba’s canola crop is off to a good start because of a wet spring.
However, the moist conditions have also prompted growers to load up their sprayers with fungicide for blackleg.
“It’s everywhere, and we know that there is a level of pressure and a level of the disease that we’re probably going to see in almost every field,” said Canola Council of Canada agronomy specialist Angela Brackenreed.
Wet spring weather enables the blackleg pathogen to become established. The disease can greatly reduce yields if the weather becomes hot and dry later in the season.
It is early in the year to see signs of blackleg, but on some fields it’s already getting too late for producers to effectively treat their canola with fungicides.
“The earlier the better for a fungicide application for control of blackleg,” Brackenreed said.
“If you can get in by that one or two leaf stage, you can expect to see improved efficacy by that fungicide.”
Some producers tank mix fungicide with their first in-crop herbicide application to avoid an extra pass with their sprayer, which can push the treatment past the two to three leaf stage.
However, splitting the applications and having an extra sprayer pass can mean the application may not provide the return on investment to make the fungicide worthwhile.
Brackenreed said the canola council does not recommend every grower use a fungicide on every canola field.
Instead, producers need to know if they are in a high-risk situation for the pathogen before they decide to spray.
“It’s one of those things, similar to a sclerotinia fungicide application — you really have to be proactive with it: look at your rotational history, what’s been the blackleg pressure in the past, what are environmental conditions like, et cetera,” she said.
Longer rotations are the main way producers can reduce blackleg pressure.
Brackenreed said the initial recommendation of a four-year rotation was made before blackleg resistance was bred into canola.
“The reason for that is they felt that four years was enough time to let the pathogen break down on stubble and then population wasn’t high enough to pose a significant threat to the canola when you got to that fourth year,” she said.
Even canola varieties resistant to blackleg are vulnerable to the disease.
“A resistant variety does not mean immunity,” she said.
“As we see some pathogen shifting happening because of the amount of pressure we are putting on that resistance, we are seeing more and more of it (blackleg) in our resistant varieties.”
She said growers can help prolong blackleg resistance by lengthening their rotations using different companies’ blackleg-resistant varieties.
Brackenreed said resistance will break down if repeatedly tested by the same tools.
The canola council encourages producers to perform crop trials on their farms to see if the crop protection products they are using are worth the effort and cost. There is still time to run fungicide trials on some fields, she added.
“I really encourage folks to do some trialling on their farm and see on their own farm what is the return from using products like this, and if they are efficacious on a field to field basis,” she said.