Integrated management advised for clubroot

One hundred million spores per gram of soil was the highest concentration in Brittany Hennig’s greenhouse trial. It was the only concentration with visual above ground symptoms. A susceptible variety is on the left and a clubroot resistant variety is on the right.  |  Brittany Hennig photos

Resistant varieties, hydrated lime applications and improvements to weed management appear to be beneficial

RED DEER — New preliminary research suggests farmers will be able to better manage clubroot if they integrate a number of practices.

The University of Alberta trials, led by plant science masters student Brittany Hennig, indicates that producers who use multiple strategies, like growing resistant varieties, using lime to spot-treat, and better controlling weeds, will have a greater chance at warding off the disease.

“Don’t rely on one single method,” Hennig said in an interview after sharing the findings Jan. 7 at the Agronomy Update conference in Red Deer.

“My results showed using resistant varieties is great, and that adding lime, managing our weeds and doing a three-year rotation can be more helpful,” she said. “These things are all very easy to do.”

Clubroot is a serious disease that can hamper canola yield and quality, as well as potentially destroy an entire crop if infestation levels are high.

The disease continues to spread in Alberta, with latest figures showing it’s in 42 counties in the province. As well, resistance in varieties has been breaking down.

“Unfortunately, some of the new cases were severely infested,” Hennig said. “These new cases were found on clubroot-resistant canola, so it was a double whammy for those producers.”

To get her results, Hennig conducted two separate trials.

In one, she tested to see how resistant or non-resistant varieties would grow in soil with zero or heavy infestation.

The trial involved a four-crop rotation. Each crop was grown for eight weeks in a greenhouse. There was a one-week break before the subsequent crop was planted.

The crops were grown in tubs and it took about 11 months to complete the rotation.

Rotations included:

  • Clubroot-resistant canola, wheat, barley, clubroot-resistant canola.
  • Clubroot-resistant canola, wheat, barley, clubroot-susceptible canola.
  • Clubroot-susceptible canola, wheat, barley, clubroot-resistant canola.
  • Clubroot-susceptible canola, wheat, barley, clubroot-susceptible canola.

The rotations were grown in soils with spore loads of zero spores per gram of soil, 100 spores per gram of soil, 10,000, one million and 100 million.

The trials haven’t been duplicated yet, she said, so growers should take the results with a grain of salt.

What she found, however, was that rotations with clubroot-resistant canola had fewer disease symptoms than rotations that had clubroot-susceptible canola.

“What I hope we take away from this is that we want to get a jump start on managing these spore loads and stick with using resistant cultivars,” she said.

Producers should also be pulling out crops to inspect them for symptoms, she added, because even in cases of one million spores per gram of soil, there were no above-ground symptoms.

In her second trial, Hennig applied lime to see whether it had an impact on clubroot.

It was conducted in a split-plot design, and genetics and weeds were taken into account.

No herbicides were applied. Hennig explained this would be the equivalent of a farmer not wanting to spray a difficult area, or of a farmer not slowing down at corners when doing a herbicide application.

With the lime application, Hennig aimed for a desired pH of 7.2, which she said is a desirable pH for clubroot management. It’s not a pH for nutrient movement.

Lime applications levels will vary per farm, considering that soils will be different, she said. Farmers should always get a lime application recommendation off their soil sample, she added, and they should ask what method is being used to create the application.

Between her two sites, she only needed 3.5 to 6.5 tonnes of lime application per acre.

She found that using lime helped reduce the incidence of disease.

“What we can say here is hydrated lime can complement the use of clubroot-resistant genetics,” she said.

Lime is hardly used by canola growers, but researchers have been figuring out how it can work for prairie growers in a way that’s affordable and practical.

Currently, the canola industry has promoted using it in a small-scale way to manage patches of infestation. Hennig said no one is recommending entire fields be limed because it can have significant consequences if over-applied.

“We’re trying to start small and work our way there,” she said.

Hennig plans on replicating her trials to see if the data holds up. She also plans on measuring spore-load concentrations to measure the consequences of not implementing an integrated clubroot management plan.

“Hopefully I can determine an effective recipe for canola growers,” she said.

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