*[UPDATED: Dec. 28, 2018] Still growing a canola-wheat rotation? One more year between canola crops could make a huge difference when it comes to clubroot.
“Recent research has shown that 95 to 99 per cent of spores die over a two-year break,” said Dan Orchard, agronomy specialist with the Canola Council of Canada.
“We were told it lasts for 18 or 20 years, so we didn’t think crop rotation would have the impact that it does have.
“This is very key information that we didn’t know.”
Growing canola every other year has become the preferred rotation for many (although some are still growing back-to-back canola crops despite the risks). But as clubroot spreads — at a rate of 300 new fields a year in Alberta — more and more producers are coming around to the idea of extending their rotations, said Orchard, who spoke at a recent Alberta Canola Powering Your Profits event.
“Rotation is starting to catch on now,” he said. “People are starting to proactively manage clubroot by rotating and not waiting until they get clubroot.”
But the new research has an ominous flip side — once infestations reach a certain level, clubroot can turn into a monster that could take a generation to beat back.
Canola crops typically won’t start dying from clubroot until the spore load in the soil reaches around 100,000 spores per gram of soil. So fields with low spore loads could become symptom free once they’re rotated out of canola or another host crop for two years.
“If you’re at 100,000 spores and only one per cent of them live, you shouldn’t see symptoms after a two-year break,” said Orchard. “That break from canola is really key.”
But in fields with millions of spores — like those in much of central Alberta — the two-year break won’t decrease the spore loads enough to prevent the plants from dying.
“That’s the issue in north-central Alberta,” said Orchard. “Our spore loads got so high from not rotating long enough out of canola that it’s really a lot more difficult to control now.”
Any of the spores that are hardy enough to survive past a two-year break from canola will live in the soil for up to 18 years, he added.
“There’s always going to be some in the soil. It’s impossible to eradicate, but certainly we can do our best to decrease spore levels.”
There are a few ways producers can do that, in addition to extending their rotations.
“I think everybody will end up having clubroot. It’s just that difficult to keep away,” said Orchard. “But a lot of the ways clubroot spreads is in your control.”
It’s not going to be easy, he added. The canola council has a series of recommended prevention strategies that simply aren’t being followed by most producers because of the time and work associated with them.
“We found that growers would read the checklist until they got to something they couldn’t do, and then they’d just throw the list away,” said Orchard.
“Really, the only management technique I’ve seen deployed in the last 10 years is resistance.”
And that resistance is starting to break down.
New strains of clubroot have adapted to overcome the resistance in current genetics, and to date, more than 150 fields in Alberta have a new pathotype that can’t be controlled with current resistant varieties.
“If that soil is spread to your farm, that’s where the trouble begins,” he said. “If we don’t change something from that first round of clubroot that moved around at 30 kilometres a year, these new pathotypes are going to do the same thing.”
The best way to prevent the spread of clubroot is by sanitizing equipment. If producers knock the loose, visible dirt off their equipment before it enters the field, they can reduce the risk of getting clubroot or transmitting it by 90 to 95 per cent. If they add a bleach solution to that, they can reduce their risk even further, by 99.9 per cent.
“If it’s June 8, and you’ve got 3,200 acres to seed, I’d be surprised to see many guys doing this,” said Orchard. “But research has shown that there’s a 99.9 per cent chance of not moving clubroot around by doing that.
“It’s a really important step.”
‘Vaccinate’ that field
Even so, clubroot can find its way into the field by being transported by dust storms, wildlife, and water movement, so some risk remains even if a producer does everything right.
“You can do everything possible to minimize and reduce the amount that shows up on your farm, but there are some means by which it will arrive that are out of your control,” said Orchard.
That’s where resistant varieties play an important role.
“The question we get asked a lot is, ‘Should I put a resistant variety in the field before clubroot arrives?’ The answer is absolutely yes,” he said.
“It’s like a vaccination. You don’t get vaccinated for the flu after you get the flu. You do it before. So you need to deploy these before you get clubroot if at all possible.”
If that’s not possible, scout regularly and switch to resistant varieties if clubroot is becoming an issue. But even then, rotation is critical.
“Quite frankly, some of the areas that the resistant varieties got funnelled into were able to grow more canola because they had access to resistant varieties, which has kind of backfired,” said Orchard. “You still need that two-year or three-year break, even when you’re using resistance.
“It’s way easier said than done for me to stand here and tell you to grow more crops. It’s not something you can just jump into, but I’d try to grow more crops if you can.”
*UPDATE: A previous headline indicated a “two-year rotation” that did not reflect the information in the story. The headline has been updated to indicate a “two-year break” can reduce clubroot spore loads.