Is clubroot spread in Sask. unavoidable?

There’s good news and bad news for Saskatchewan canola growers concerned about clubroot.

The bad news is the disease will likely become more prevalent in the province as annual canola plantings continue to rise.

The good news is that clubroot can be managed if growers catch it early and follow some simple management rules, such as lengthening rotations and adopting good in-field sanitation practices.

“I’m quite convinced that clubroot will come to your farm. It’s just too hard to keep it away,” said Dan Orchard, an agronomist and clubroot expert with the Canola Council of Canada.

“But you can keep its impact down to a minimum amount by finding it early…. The key is to keep spore loads low.”

At a recent oilseed producers’ meeting held in North Battleford, Sask., Orchard said Saskatchewan is in a much better position to manage clubroot than Alberta was 10 or 15 years ago.

When clubroot was first discovered in Alberta in 2003, little was known about the disease or how it spreads.

The learning curve was steep in Alberta. By the time growers were learning how to manage the disease, many fields in Alberta’s northern grain growing region were already heavily infected.

Saskatchewan growers can learn from the Alberta experience, Orchard said.

The key to successful management is to test for the disease and take action before spore loads become prohibitive.

“There’s a whole host of management strategies that you can deploy if you catch it early,” he said.

“But if you catch it late, there aren’t many options.”

Clubroot spores are incredibly small and can spread in many ways.

They can be carried by wind, water and wildlife.

They can even survive after being eaten by livestock, meaning manure and manure spreaders are other possible vectors.

The most common method of transmission, however, is via trucks, tires and farm machinery.

Spore loads are typically highest at entrances to fields or along trails that carry machinery, Orchard said.

After establishing a foothold, the spores are typically dragged to other areas of the field during tillage or seeding operations.

Recent research suggests that 95 to 99 percent of the clubroot spores in a field are no longer viable after a two-year rotational break from canola.

However, spore loads are incredibly high in some Alberta locations.

In some areas, rates of one billion spores per gram of soil have been recorded.

At that level, a two-year break would still result in viable spore loads of 10 to 50 million spores per gram of soil, easily enough to have a noticeable impact on canola yields.

In Saskatchewan and Manitoba, documented spore loads are more typically 50,000 to 100,000 spores per gram.

At those levels, a two-year rotational break is an effective management tool.

Although documented cases of clubroot are still relatively few in Saskatchewan, conditions are ripe for the disease to spread.

Over the past two decades, annual canola plantings across the West have been increasing steadily and rotations have been shortened on many farms, said canola council agronomist Ian Epp, who also spoke at the North Battleford event.

Epp stressed the importance of good sanitation and longer rotations as measures that can minimize production risks.

“Your neighbours might have it, but if you have good sanitation practices and good rotations, you’re less likely to be affected,” he said.

Testing soil for the presence of clubroot spores is an obvious element of any preventive action plan.

Soil tests taken near field entrances are a useful indicator.

Growers should also make an extra effort to control wild mustard, shepherd’s purse and stinkweed, which are common prairie weeds that can produce clubroot galls and contribute to the spread of the disease.

Saskatchewan conducts an annual survey to monitor the spread and prevalence of clubroot and other common canola diseases.

Barb Ziesman, plant disease specialist with Saskatchewan Agriculture, said the survey involves collecting soil samples that are screened for the presence of clubroot DNA.

Only two soil samples have shown spore levels above 1,000 spores per gram of soil over 10 years of testing.

At the same time, the Saskatchewan Clubroot Initiative has confirmed the presence of the disease in fields that were not included in the annual survey.

Two positive cases were confirmed in 2011. The disease was also confirmed in 2017 in an unspecified number of fields in Saskatchewan crops districts 9A and 9B.

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