Predicting which diseases will cause problems on your farm this year is a little like predicting the weather — you know it’s going to hit you, but you don’t know when or how bad it will be.
And it doesn’t help that these two unpredictable forces often go hand in hand.
“One of the primary drivers of what we’re going to see this year is going to be the weather,” said provincial research scientist Michael Harding. “Because that’s so challenging to predict more than two or three days out, we’re going to have to take a bit of a wait-and-see approach to really know what’s going to take a run at us in 2021.”
But like a weather forecast, the current conditions will offer some clues as to what producers might expect to see in their fields this year, said Harding. And that starts with a look at last year’s growing season.
“It was a real mixed bag,” he said. “We started out pretty wet, but then it did get drier in some parts of the province and stayed wet in other parts.
“So we had some areas that got hit pretty hard with certain diseases, and we had other areas where the environment wasn’t quite as conducive.”
In canola, blackleg and sclerotinia levels were down across the province, but clubroot continued its spread, with about 10 per cent of the 620 fields surveyed showing symptoms of the disease (with 90 per cent having intermediate or high levels of clubroot).
“For clubroot, we definitely had a lot of new fields reporting positive,” said Harding, adding three new counties reported clubroot for the first time in 2020.
“That brings us to about 66 or 67 per cent of the counties or municipal districts in the province of Alberta positive for clubroot now. That’s a bit staggering when you consider that 20 years ago, there were zero fields of canola with clubroot.
“For a soil-borne disease, it’s spread very, very quickly.”
Even more troubling is that some of these fields were growing clubroot-resistant cultivars.
“If there’s anybody growing canola in Alberta who doesn’t have clubroot, that’s great,” said Harding. “But if you think it’s never going to show up in canola in your area, what we’re seeing doesn’t suggest that.
“What we’re seeing suggests that clubroot will continue to spread.”
Pulse and cereal diseases
Peas in some areas were also hit hard last year by an ever-present threat — root rots.
Most fields surveyed had fusarium root rot, while aphanomyces were found in an increasing number of fields.
“The incidence of root rot — the per cent of plants that had the disease — on average was around 65 per cent,” he said, adding roughly two-thirds of the plants had symptoms, some so severe that there were economic losses.
“Root rots in peas and lentils continue to be a real challenge.”
Mycosphaerella is another ongoing issue for peas and, again, “we see it pretty much everywhere we go,” said Harding. “But the incidence was really high in 2020 — almost 95 per cent of the plants that we looked at had mycosphaerella or ascochyta on the leaves and/or stems. On an index of zero to 100, about 40 per cent was the average. It was a year that mycosphaerella in peas was pretty significant.”
For wheat growers, fusarium head blight may have been less severe last year depending on the location, but it still needs to be on the radar.
“When we have dry years and we don’t see a lot of head blight, it doesn’t mean that fusarium graminearum has gone away,” he said. “It can still hang around in crop residues and other host crops, and then in a year where we get a lot of rainfall or humidity during anthesis, it can cause a lot of loss — some yield loss, but more of a downgrading loss.”
And where that downgrading is occurring has started to shift, he added.
“Like clubroot, it’s continuing to move around into parts of the province that have never had to deal with it before,” he said.
“In 2019 for the very first time, there were more samples in northern Alberta downgraded due to fusarium-damaged kernels than there was in the south. Between 30 and 50 per cent of the samples in central and northern Alberta were downgraded due to fusarium-damaged kernels, whereas in southern Alberta, it was less than 10 per cent.
“We think of fusarium head blight as a southern Alberta problem, but that’s changing. No matter where you are in Alberta now, this is a disease you need to be aware of and ready to manage.”
For diseases like fusarium head blight that are weather dependent, risk maps can help. But other diseases are trickier to predict.
“For a lot of the other diseases, it’s a complicated interplay of host, pathogen, and environment. Depending on those three things and how they come together, that’s going to determine risk,” said Harding.
Generally, plant pathogens do well in wet conditions at temperatures between 15 C and 30 C, as pathogens have a hard time multiplying in drier, cooler conditions.
“If it’s cold and dry, we don’t see a lot of disease, but if it’s warm and wet, that’s when we usually see the maximum.”
Those things will largely be outside of a producer’s control, so you’ll need to make sure you have a strong foundation of crop rotation and resistant genetics, he said.
“Producers know what the usual suspects are on their farm,” said Harding. “When you think about risk and what you’re going to do for 2021, you really need to start with the usual suspects that you know you’re going to have to do battle with.
“Then you need to use the management practices that will help you get ahead of it, and most of those things are going to be situational and incremental. But if you have a good rotation and you’re using the best resistant genetics, that’s going to get you a long ways to managing these diseases.”