Even as growers are urged to better use resistant varieties, they are also encouraged to improve their rotation practices
Clubroot is everywhere.
The soil-borne disease is present in canola fields in Manitoba’s Interlake and can be found 1,400 kilometres west in the region around Edmonton.
While it’s a serious disease and represents a long-term risk for the sustainability of canola production, many producers aren’t using genetic tools to ward off clubroot.
Less than half of growers are seeding canola with resistance to clubroot, a disease where galls form on canola roots and can cause premature death of the plant.
“You start looking at the statistics … and fewer than 50 percent of the acres had clubroot-resistant genetics,” said Chad Koscielny, North American canola breeding lead for Corteva Agriscience.
The percentage is likely higher in Alberta, where farmers in central Alberta have been dealing with clubroot for more than 15 years, which means the number of growers in Manitoba and Saskatchewan who use clubroot resistant seed is well below 50 percent.
“We’ve been increasing the rate at which growers are adopting clubroot resistant (hybrids), but we’ve still got a long way to go,” Koscielny said.
The Canola Council of Canada and seed companies say that number should be much higher than 50 percent.
Ideally, every acre of canola in Canada will soon have resistant genetics.
“The goal will be to have clubroot resistance in all varieties — it will sort of be like ‘table stakes’ in the future,” said Dan Orchard, Canola Council of Canada agronomist in Alberta.
“Researchers support this idea, as does the canola council and life science companies.”
For now, that’s probably not possible.
Many canola hybrids in the marketplace don’t have resistance to clubroot.
“It takes time to bring new varieties to market, and those which are entering the market now were being developed years ago so may not include the resistance genes,” Orchard said in an email.
However, a council Q&A document says clubroot resistant (CR) varieties should be used in fields where no clubroot is present.
“Especially if there are infested fields in the region. Growers cannot be 100 percent certain the pathogen is not in their field. CR varieties can prevent spore buildup even if it is at undetectable levels,” the pamphlet says.
Koscielny said Corteva’s canola lineup will soon comprise only clubroot resistant varieties, but the company has a clear message for growers: clubroot can’t be solved by science alone.
Put another way — plant breeders need help.
“It needs to be a collaboration. It needs to be a partnership between the researchers, the seed developers and growers,” said Koscielny, who joined Pioneer in 2003 and works out of Corteva’s research centre in Carman, Man.
In practical terms, the collaboration means growers should adopt a one in three canola rotation because it dramatically reduces the amount of clubroot spores in the soil. Research suggests a two-year break between canola crops reduces the spore load by 90 percent or more.
If growers don’t adhere to the one in three rotation, clubroot spore counts remain high and new strains of the disease are likely to emerge.
That’s what happened in certain fields in central Alberta.
“In that Edmonton region where the (genetic) resistance did break down … there wasn’t one in three rotations. It was really (a case of) pushing the resistance as hard as you could,” Koscielny said.
Some growers might be tempted to grow canola every second year and rotate resistance genetics to manage clubroot.
Such a strategy is short-term thinking and risky because clubroot will build up in the soil and eventually overcome the resistant genes.
That puts pressure on canola breeders like Koscielny to develop new forms of clubroot resistance. At some point, the well of new genetic resistance could dry up.
“That’s why our first and foremost recommendation is to follow the canola council one in three crop rotation,” he said.
“The second one is to use clubroot resistant genetics, right out of the gate.”
If the canola industry burns through genetic resistance in short order, public and private plant breeders must expend more energy on clubroot.
It’s a classic case of opportunity cost — reduced time that can be spent on other traits, perhaps frost and cold soil tolerance, which could push yields much higher.
One of the key lessons from central Alberta is the consequence of big numbers.
Once spore counts climb into the billions per gram of soil, it’s very difficult to get clubroot under control. Extending the break between canola will reduce the number, but it can take years to get it back to a manageable level.
“Listening to the growers and attending different meetings in Alberta … one common theme that I heard every one of them talk about, is they wished they had managed their spore load earlier,” Koscielny said.