Fifteen years ago, Dan Orchard was working as an agronomist at a retailer when he got a phone call about something “funny” in a customer’s canola field.
The plants were prematurely ripened and the roots looked strange. Orchard had a hunch of what he was looking at, but a visit with a plant pathologist confirmed his suspicions.
Orchard had just found the first case of clubroot in canola in Alberta.
“In hindsight, that first case was quite bad,” said Orchard, now an agronomy specialist with the Canola Council of Canada. “The whole field was infested, but we still thought it wasn’t going to move around much. We weren’t that scared of it, and that was part of the problem.
“We didn’t understand it well enough to understand the impact it was going to have and how quickly it would move.”
And for the first couple of years, it was dry and clubroot really didn’t spread that quickly. Spore loads were low and infested patches small, and so farmers didn’t realize they had a real problem on their hands until it was too late.
“We now know that this does move around very freely, but I don’t think farmers realized how quickly it was going to create problems from a small patch to a whole field,” said Orchard.
“And because of that, they didn’t take a long enough break from canola. They just kept growing it, usually every second year.”
Fusarium head blight
And every other year, fields were typically put into cereals — leading to a corresponding rise in fusarium head blight.
“It’s been in Alberta for decades but fortunately, the fusarium management plan really helped prevent the spread of fusarium graminearum early on,” said Trevor Blois, disease diagnostician with 20/20 Seed Labs.
“But as time has gone on, it has spread from field to field, and I think that’s a big reason as to why we’re seeing it everywhere now.”
Fifteen years ago, fusarium was isolated to southern Alberta, but it didn’t take long for it to start spreading north, said Blois. In 2007, the first case of it was found in central Alberta, and since then, it has continued to spread, with increasing disease levels and severity across central Alberta and into Peace Country.
Part of that has to do with the weather. Disease levels peaked in 2016 — a wet year — but both 2017 and 2018 were drier, limiting the spread and severity.
Even so, as long as these shorter crop rotations continue, the disease will continue to spread, he said.
“For fusarium graminearum, if nothing is in the field for two or three years, it’s going to decrease the inoculum levels much quicker,” said Blois.
“If there isn’t as much host around, you’re not going to be seeing the disease be nearly as dominant. So if cereals were not grown nearly as much, it would help.
“It’s not really a solution though. People still need to grow cereals.”
Scrapping canola from the rotation wasn’t a viable solution for clubroot either, said Orchard. When first discovered, clubroot spores were believed to live in the soil for up to 20 years — and no one was about to take a 20-year break from canola.
But at the time, there weren’t really any other tools that farmers could use to combat its spread.
“‘Don’t grow canola’ was pretty much the only management tool that was available 15 years ago,” said Orchard, adding researchers have recently learned a two-year break between canola crops can reduce spore loads by up to 99 per cent.
By the time that resistant varieties started coming out in 2010, some fields in north-central Alberta were already heavily infested with clubroot, putting pressure on that new resistance.
Now, 15 years after the first case was found, clubroot strains are shifting to overcome resistance, and those new strains are starting to move around — sparking the second wave of clubroot infestation in north-central Alberta.
“We’ve overrelied on our genetics and the resistant varieties to be a silver bullet for this disease,” said Orchard. “And now we’re quickly realizing that’s not the case.”
And as clubroot continues to spread — at a rate of 30 kilometres a year in all directions — farmers have been left playing catch-up to minimize the damage.
“We’re very reactive now because we didn’t have the science and education to know what to do about it back then,” said Orchard. “Now that we do, we’re chasing this disease around and sinking more and more money into research to try and get ahead of it.
“Something needs to change, but nothing has been done.”
And if nothing changes, clubroot will “just continue marching across the Prairies.”
“If we don’t get ahead of it and we don’t start changing some of our management practices, there will be far less canola grown in the areas where clubroot has already been for 15 years,” he said.
“But if we up our game and start to really deploy these management practices, I think it could be slowed down significantly and have not much more of an impact than it already has.”
However, keeping spore loads down means doing everything ‘right’ — extending rotations, deploying resistant varieties, sanitizing equipment, and regular scouting.
“If your spore loads are low and you’re on a three- or four-year rotation with a resistant variety, I suspect you’d never see clubroot symptoms,” said Orchard. “I could see that for clubroot — if we can slow it down enough and buy enough time.”
But time is running out.
Resistant varieties were the “low-hanging fruit,” but genetic resistance is already failing. It takes at least 10 years to bring a new variety to market, and any next-generation genetics hitting the market today are already almost too late.
“Really the only management practice that’s been actively deployed is the use of resistant varieties — but that’s only one tool,” he said. “It’s the biggest hammer in the tool box for sure, but now people are realizing it’s time to pull out the little tools instead of this great big hammer all the time.”
With new strains being found every year — and no genetics able to resist them — farmers will need to start looking at even more stringent management practices, such as liming fields, grassing entranceways, and sanitizing equipment.
“We’ve learned so much since clubroot was first found, and we have great management strategies now. But we can’t just talk about them — we need to actually do them,” said Orchard.
“We put a lot of trust in our researchers who were breeding resistant varieties. Now we need to put an equal amount of trust in our researchers who are looking at other management strategies.”