Sclerotinia can reduce canola yields by up to 50 per cent — but a well-timed fungicide application can prevent some of those losses
It may be a little bit early to guess, but canola agronomist Keith Gabert predicts that sclerotinia will be a problem in canola crops this summer.
“We always assume that we’re going to have sclerotinia issues,” said the Canola Council of Canada agronomist. “Typically, sclerotinia germinates under good moisture conditions, so we’re making the assumption that unless it’s a drought, you have sclerotinia somewhere in the field.”
Seeding conditions this spring were “quite wet,” but moisture levels so far this season haven’t been excessive, depending on the growing area, Gabert said at CanolaPALOOZA in late June.
“Sclerotinia is driven by moisture. If your crop canopy has moisture in it and you had rain, we look at using a well-timed fungicide application as a preventive insurance-type application,” he said, adding the right time to spray is between 20 and 50 per cent bloom.
“If you have apothecia (or fruiting bodies), that’s high risk, and we’ll probably ask you to spray. If you don’t find apothecia, we still think it’s a risk and we’ll probably ask you to spray.”
At that point, producers should go in with “a good-quality fungicide and high water volume — something we can get a good coating on the petals that are there and try to protect that early window of flowering.”
But it’s important to target the other parts of the plant as well, he added. “That tends to be where we see the most yield penalty — if we get infections on the main stem.”
Last year — with its frequent rainfalls that lasted for the bulk of the growing season — was the exception.
“We had sclerotinia infections on all parts of the plants all throughout the growing season,” said Gabert. “If a grower sprayed three times, he might have thought that was an economical attack plan, but the first application didn’t seem to do that much. And when that fungicide becomes less effective after 10 or 14 days, we still saw a lot of infection.”
And while those weather conditions usually push canola yields up — “We had growers with 30 to 50 per cent infection of sclerotinia seeing 40 to 50 bushels” — the potential yields were likely half again higher.
“If a grower tells me that he has 50 per cent sclerotinia infection and 40-bushel yield, it probably means there was 20 bushels lost to disease,” said Gabert. “He had a 60-bushel crop that we couldn’t get for him because we’re not managing the disease aggressively enough.”
Sclerotinia is largely driven by past cropping history, he said.
“With last year being particularly bad and knowing that a lot of growers are on a wheat-canola rotation, I’m looking at 2018 as being back on that same land with really high inoculum levels in the soil,” he said. “Given high moisture, that would be a really bad recipe for sclerotinia.”
Growing tolerant varieties and employing split applications of fungicide will help manage it, but “it’s a really aggressive disease.”
“Every broadleaf crop can get it. Chances are it’s in your field and moisture is going to push it forward,” he said. “It’s always something to watch out for.”
Clubroot, on the other hand, is “a little easier to predict,” said Gabert.
“If you’ve scouted for it, you have a bit of an idea if it’s in your field,” said Gabert, adding the number of infected fields across the province is growing exponentially.
“The one dry year, we had a bit of a dip in terms of numbers of fields reported, but just as a rough rule of thumb, I fully anticipate 300 to 400 new fields reported every year if there’s any kind of adequate moisture.”
Resistant varieties have worked “exceptionally well,” especially where they have been deployed before clubroot builds up in the field, but ultimately, producers need to avoid moving soil around.
“I know it’s not something we want to think about, but when we find clubroot in the field, 90 per cent of the time, it’s near the approach the grower uses,” said Gabert. “It’s pretty clear in most cases that it’s coming with ag equipment.”
Sanitizing equipment can help manage that, but it needs to be practical for growers.
“If we tell you to clean every piece of equipment every time it moves on and off your farm, you might not be pleased to do that much,” said Gabert. “If you have multiple points of entry onto your farm, it becomes harder to manage. But if you have a relatively closed farm and you put a little more effort into keeping that soil out, you may be able to prevent it from coming in.”
If you buy a piece of equipment from an area that has clubroot in it, clean it before you leave the area and before you get to the farm.
“For a lot of growers, they only bring in a new piece of equipment every year or two, especially something that moves soil like a disc or air seeder,” said Gabert. “If you can make sure it doesn’t bring clubroot onto your farm, maybe that’s only a once every two- or three-year exercise.”
And if there’s already clubroot in your field, the best thing you can do is lengthen your canola rotation.
“We know if we put clubroot-resistant varieties in a field where the pressure is high, as little as two rotations will give us patches where the resistance is no longer working,” said Gabert. “If we want to keep those tools for the industry to keep using, we need to try to avoid clubroot as much as possible.”