Clubroot is the deadliest disease of canola in Western Canada, capable of causing huge yield losses in infected fields.
While the disease continues to spread, prairie farmers are fighting back. Two methods favoured by canola producers are deploying clubroot-resistant canola hybrids and lengthening crop rotations, but it’s important not to overlook another key strategy for controlling clubroot: eliminating the threat posed by canola volunteers.
Volunteer canola isn’t just a weed that will compete with canola and other crops for essential nutrients and water – it can also be a primary source of clubroot contagion in farmers’ fields.
Infected canola volunteers and other susceptible weeds, such as shepherd’s purse, stinkweed, wild mustard and flixweed, will spread the disease in canola crops and add to the inoculum load in the soil, where clubroot spores can persist for up to 17 years.
This is why many experts, like Chad Koscielny of Corteva Agriscience, maintain it’s important to get an early jump on canola volunteers and other potential clubroot hosts before seeding canola.
“Volunteer canola is still a fairly weedy species, so it can get acclimated to some of those colder temperatures in spring and start growing even before your crop is planted,” says Koscielny, the North American canola breeding lead at Corteva Agriscience.
Koscielny says it’s been learned that if clubroot is present in a field, it can take non-resistant canola volunteers only four weeks from emergence to become infected and start forming galls.
“When I heard that timeline, that’s when I realized, ‘Wow, this is something that farmers really need to pay attention to here,’” he says.
As Igor Falak, technology lead at Corteva Agriscience, points out, it’s possible for canola volunteers that are derived from resistant canola hybrids to still play host to clubroot, due to the process known as genetic segregation.
“In the long run, it’s not good to have any canola volunteers in a field, whether they’re susceptible or resistant to clubroot,” he says.
If canola volunteers and host weeds aren’t effectively controlled at the start before a true canola crop emerges, Doug Moisey, an agronomist with Corteva Agriscience’s Pioneer Seeds Division, says there’s a greater chance clubroot will take hold in the field, leading to an increase in disease load and reduced yields come harvest time.
“This is why it’s so critical to control volunteer canola and host weeds early,” Moisey says. He believes a pre-seed herbicide application is the best precaution for controlling canola volunteers and host weeds that can propagate the clubroot pathogens in canola fields.
Moisey says canola growers should be just as vigilant when growing other crops in their rotation, such as wheat and barley. That’s because infected plants will increase pathogen spore loads within the soil, increasing clubroot pressure on a true canola crop when it is planted in that field.
Moisey maintains another reason for controlling volunteers and hosts early is to mitigate potential spore production and reduce the movement of clubroot spores within a field.
According to Falak, fields that have a high concentration of clubroot inoculum can cause several problems for farmers, such as a breakdown in genetic resistance in clubroot-resistant canola hybrids and the emergence of more virulent pathotypes of the disease.
This season, western Canadian farmers looking to beef up their clubroot management plans have another tool at their disposal: a new canola pre-seed herbicide from Corteva Agriscience called Prospect.
Prospect contains both Group 4 and Group 14 active ingredients, so when it is tank-mixed with glyphosate in a pre-seed burndown, it delivers three different modes of action control on problem weeds.
Combining modes of action not only delays the onset of herbicide resistance, but will also provide more complete control than glyphosate alone. Prospect can also be applied with five to 10 gallons of spray water volume per acre without giving up performance in weed control.
Moisey sees Prospect as an effective counterpunch to the clubroot threat posed by canola volunteers and other potential weed hosts, adding it’s a great fit for growers looking for a clean field to ensure the best start for their canola crop.
Healthy plants stand a better chance of withstanding pressure from diseases like clubroot, which can go a long way towards maximizing a canola crop’s yield potential, Moisey adds.
“If a canola plant starts out big and healthy, then it’s off to the races,” he says.