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Clubroot: Coming soon to a canola field near you

Manitoba Agriculture tour offers insights and strategies on clubroot management

Clubroot isn’t yet a significant challenge for Manitoba canola growers. But the emphasis these days is on ‘yet.’

The first cases in the province were discovered in 2013, and more cases are popping up every year. Last August Manitoba Agriculture announced a further eight.

That demonstrates how the disease has persistently and stubbornly survived and spread since it was first discovered in the Edmonton area in 2003. The soil-borne disease causes bulbous growths knowns as galls on the roots of canola plants and can lead to early ripening and plant death. Dan Orchard is the Canola Council of Canada agronomist who first spotted clubroot in Western Canada, and he cautioned growers it isn’t always easy to see.

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“It’s not very easy to spot above ground,” noted Orchard. “Below ground it can get really nasty before the above-ground symptoms appear, so we need to pull lots of plants.”

Manitoba Agriculture and Manitoba Canola Growers Association have organized an information tour that is travelling from town to town in the province to raise clubroot awareness. The tour began on January 30 in Manitou and passed through Portage la Prairie, Brandon and Neepawa before stopping at the CropConnect conference in Winnipeg on February 14, then moving onward towards Grandview on February 20 and Steinbach on February 21.

Orchard said it is not uncommon for farmers to see a spot in the field where the plant height isn’t as high as the surrounding areas and assume that it’s just a wet spot in the field. However, in many cases it can be indicative of clubroot.

Orchard delved into the ways that growers can limit the spread of clubroot when it is discovered. Clubroot spreads through the movement of dust and soil, which is mostly in the control of the farmer. So cleaning equipment is a critical step.

“We’ve been preaching sanitation,” Orchard said.

The map shows positive clubroot findings by RMs, which have been highlighted to show the highest concentration of spores. This does not mean all fields in the RM have these concentrations. As spore concentrations can be highly variable within a field, the RM classification indicates only the maximum concentration found in any field in the RM. Further explanation on the concentration categories are as follows: RED = Symptoms observed: Clubroot symptoms have been observed in fields in this RM. Management to prevent continued buildup or spread of this pest should be implemented. ORANGE = 10,001 to 80,000 spores/gram soil: Spores have been found in fields in this RM at concentrations approaching levels known to cause field symptoms. Without management, concentrations may increase to where symptoms are visible. YELLOW = 1,001 to 10,000 spores/gram soil: Clubroot spores have been found in this RM at low to intermediate levels. With proper management, spore concentrations can decline. GREEN = zero to 1,000 spores/gram soil: Clubroot spores have not been detected, or detected at very low levels. At this concentration, clubroot is not a major concern, but fields should be monitored. Retesting is recommended within the next five years. It is generally reported that 100,000 spores/gram of soil are required to see symptoms under field conditions, but symptoms can still appear under favourable conditions. As less than 10 per cent of farms in Manitoba have been sampled, it is recommended that all fields be tested, regardless of RM classification.
photo: Manitoba Agriculture

The canola council has resources available that outline three steps to effective sanitation: rough cleaning, fine cleaning, and disinfection. The level of sanitation depends on the perceived risk. Orchard recommends that once an infestation is detected, step one (removing visible dust and dirt from equipment) is crucial.

“For steps two and three, I would recommend you do that for anyone coming on your land,” he explained. “It’s OK if you don’t do everything, but it’s not OK if you do nothing.”

The next to speak was Alberta farmer John Guelly, who farms north of Edmonton, in the area with the most severe infestations of clubroot. Guelly discussed his personal experience of discovering clubroot on his farm five years ago and shared some of the things he would have done sooner.

He said he would have moved to a three-year rotation sooner. At the time, experts were recommending a four-year rotation. In northern Alberta, because of the shorter growing season, they have fewer crops available to rotate. So Guelly said he stuck to the wheat/canola rotation that he had been doing for years. However, while a four-year rotation is tricky in his area, he said a three-year rotation is manageable and he could have significantly reduced the impact of the infestation had he switched earlier.

He also said he shouldn’t have waited until he spotted galls in his field before he used a resistant variety.

“I knew there was clubroot confirmed not far from me,” he said. “I easily could have seeded a clubroot-resistant variety a year or two sooner.”

Lastly, he would have done more scouting in his fields.

“I always do a lot of scouting on my farm, but I wish I had done more. Scouting and knowing what to look for may have allowed me to find clubroot in my field at least a year or two sooner,” Gulley said. “Don’t miss your chance like I did.”

Michael Weir, an agronomist with Pioneer Hi-Bred from Miami, Manitoba, was the final panellist to speak. His presentation included maps of the progression of clubroot year by year since it was first discovered in Manitoba. The maps, beginning in 2014, were based on soil testing and were broken out by municipality.

Each year there was a moderate increase in spores per gram of soil. But in 2018, the numbers seemed to show a sharp increase. However, Weir suggested that was likely because there wasn’t a lot of moisture that year, so traditionally wet spots in the field were bone dry yet still showed reduced plant height, drawing attention to the problem.

Overall, Weir was optimistic. He said that Manitoba still has a low level of clubroot spores per gram of soil in most places. “It’s still under that level where we see that visual gall formation,” he said.

“If we can adopt these management practices and keep that level down, we’re going to be in good shape.”

Manitoba Agriculture’s clubroot tour continues into March with stops in Altamont on March 1, Deloraine on March 5 and Arborg on March 14.

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