Clubroot’s march through Alberta is relentless and the level of infestation here is 100 times — or even 1,000 times — worse than in Saskatchewan and Manitoba.
But there is a bit of good news: Moving to a three-year rotation is more effective than previously believed, says a Canola Council of Canada agronomist.
“New work in Canada has shown that 90 per cent of (clubroot) spores are gone after a two-year break,” Dan Orchard told an Alberta Canola Producers Commission meeting here.
“You need to have a crop rotation and it has to work. It’s up to you to decide the rotation, but this is valuable news.”
But moving from a canola-wheat rotation is a challenge for many producers, he conceded.
“How do we stretch that out to three years?” asked Orchard. “It would make such a difference and there would be fewer pathogens shifting to a new strain.”
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In 2015, more than 1,500 fields in Alberta were found to be infested with clubroot, with the disease spreading at a rate of about 30 kilometres a year. Even though 2015 was a dry year, there were still hundreds of new cases.
The new research that found there is a 90 per cent drop after two years, also concluded it takes about 20 years for the remaining 10 per cent of spores to disappear. And that’s a major problem because clubroot-infested soil in Alberta typically contains a million clubroot spores per gram. In some areas, the spore load is so heavy that a billion spores can be found in a gram of soil. This is in sharp contrast to areas of Saskatchewan and Manitoba, where an average gram of soil from an infected field contains only 10,000 spores.
“You can understand the magnitude,” said Orchard. “If you are moving a gram of soil, they need to move a wheelbarrow of soil to have the same risk. They’ve got such low levels that when they are cleaning their machinery, they need to clean everything bigger than a wheelbarrow, whereas we need to clean everything bigger than an M&M.
“It’s just a function of the spore load in the soil. We let the spore loads get too high, and now there are a billion spores in the ground.”
Orchard doesn’t want Albertan producers to forget that clubroot is a soil-borne disease, and to think about soil movement when going from a canola field to other fields.
And think twice before accepting topsoil from other areas, he warned.
“In Leduc, there’s a lot of construction and they’re giving away topsoil. I wouldn’t take it. Growers are filling in the low spots in their fields and basically spraying clubroot around their farm.”
Although new clubroot-resistant varieties have been developed, that’s not a fix and may actually be fostering new strains of the pathogen. Nine new strains were found in Alberta in recent years.
“Researchers from other countries warned us that after growing one or two resistant varieties, there could be a shift in pathotypes,” said Orchard.
As well, 32 new fields in Alberta developed big patches of clubroot even though they were growing a clubroot-resistant variety.
It’s long been known that clubroot is found at field entrances, but it can also be found at alternate entrances where equipment is pulled off at the edge of the road, entrances to highways and yards, and around grain bins. It’s also common on untreated seed and in low areas of standing water.
To fight clubroot, growers will have to look at cultural management techniques as well as genetics. A researcher in Saskatchewan is looking at older lines that have some boron tolerance. At high levels, boron can combat clubroot, but that can also kill canola. Still, older boron-tolerant lines could prove valuable, said Orchard.
“We need to look at a whole bunch of these cultural ideas rather than just throwing genetics at it every time we have a new strain,” he said. “Relying on genetics isn’t going to work. We need to have a multi-pronged approach, so things like boron-tolerant canola, liming the fields, fumigating and crop rotation.
“All of these things are going to be needed.”