The early trickle of reported clubroot infections this year could soon become a flood, says Manitoba Agriculture oilseed specialist Dane Froese.
“We have favourable conditions for the development of clubroot this year,” he said. “As with most diseases, warm moist conditions favour disease development and infection.”
Clubroot is a soil-borne disease that affects canola and other brassica species. In the past, it has been classified as a slime mould fungus but more recently it is regarded as a protist – an organism with plant, animal and fungal characteristics.
Read Also
CUSMA access key among other trade noise: Seeds Canada panel
Seeds Canada conference panelists say Canada needs to stay focused and wait as U.S. trade and tariff chaos develops, and a Canada-U.S.-Mexico Agreement review looms
Clubroot will initially infect the root hairs and as the pathogen develops, root cells are corrupted. Instead of functioning normally by taking up water and nutrients, they develop bulbous galls that stimulate cell division and choke off nutrients, ultimately leading to yield loss.
“Every gall can produce billions of spores,” Froese said. “And then those spores last in the soil for up to 25 to 30 years and can reinfect the following year.”
Resting spores can germinate and transform into zoospores, which are capable of swimming short distances in water or water-films in the soil to seek out root hairs to infect.
So far, the province has detected three new fields infected with clubroot. This adds to the 45 already detected throughout 10 municipalities in the province. Fields are considered infected if they have been confirmed to have more than 80,000 clubroot spores per gram of soil.
Those three new fields may be just the beginning. Typically, clubroot starts appearing in mid-August.
“We’ve had a warmer summer and we’ve had an abundance of moisture, so after two dry years where we didn’t see much in terms of disease spread or development, we’ve certainly seen it come back and make a bit of a resurgence this year,” said Froese.
Farmers scouting for clubroot should look for patches of prematurely ripening plants. The problem is, at a distance, these patches can be mistaken for moisture stress.
“We typically see farmers reporting higher cases of clubroot in dry years, which is somewhat counterintuitive to how the disease development actually functions,” Froese said. “We see higher infections in wetter years.”
The issue is often the result of farmers initially attributing thin patches and other spots in low areas to drowning.
“In years like 2021, where we didn’t have those excessive rains and high moisture conditions, clubroot was easier to spot because farmers weren’t looking for or expecting to have thin spots in the low areas of their field,” Froese said. “They thought those should be healthy canola plants.”
But it is those low-lying areas, where moisture collects, that are also high-risk areas for clubroot.
Froese recommends aerial imagery as an effective way to scout for the disease. There are certain hot spots and clues to look for when examining such imagery.
Farm machinery is often involved in spreading the disease, so he advises looking for streaks running in straight lines as a tell-tale symptom. Machinery might also drop infected soil during turns, so field corners are another place to look.
“Also check low spots,” Froese said. “Clubroot likes warm temperatures, and so those low spots, in those bathtub rings around us, tend to be hotspots.”
Similarly, look for any places that water runs through the soil, which can also move spores.
“Shelterbelts that act as a wind stop can stop soil erosion and can lead to soil depositing near the base of those shelterbelts,” Froese said. “That could be another point to consider.”
Once high-risk spots have been identified, dig up the plants and inspect the root system for galls. Dig rather than pull them up because the galls weaken the root system, so if they’re pulled, they will often break off at the base.
Gall development of any kind indicates yield loss is occurring, and immediate steps are needed to stay ahead of disease development in that field and the entire farm.
If clubroot is suspected or identified, contact Dane Froese at Manitoba Agriculture for assistance on next steps and for gall testing. For growers concerned about clubroot in their fields, targeted soil testing can help identify whether clubroot spores are present in high-risk areas.
Visit canolagrowers.com/in-the-lab/psi-lab/ for instructions on how to test and submit samples.
