Clubroot has been confirmed in Alberta, Saskatchewan, and Manitoba, and can cause yield losses between 30 and 100 per cent.

Sanitation, crop rotation, using resistant cultivars, and managing susceptible weeds are all useful strategies in the clubroot toolbox to mitigate infection, but what other strategies are there, and how effective are they for controlling clubroot in canola?

That’s a question that Brittany Hennig, recent graduate of the department of agriculture, food, and nutritional science at the University of Alberta, aimed to answer in her graduate studies project. She joins Kara Oosterhuis for this Canola School episode.

Although sanitation is one of the most effective management strategies to limit clubroot spread in the first place, once it’s present in a field, it’s not going anywhere; but it can be reduced. Hennig says that by using crop rotation — being out of canola or a host crop for two years — there’s a 90 per cent reduction of clubroot spores.

In her research, Hennig also looked at the effect of spore load on clubroot infection, from zero to 100 spores per gram of soil, all the way up to 100 million spores per gram of soil. She says to be mindful of the 10 per cent of spores remaining, and that they can quickly multiply in fields when a host crop is grown.

There isn’t a ton of hard data on susceptible weeds that can produce galls, and Hennig says that when considering controlling susceptible weeds, it isn’t as cut and dry.

“We plant canola at the beginning of spring and then it progresses through the season, but weeds might be a winter annual or perennial. They grow differently throughout the season,” she says, adding that distribution throughout a field of weed species and timing can affect spore loads.

For the liming strategy, Hennig says that the use of hydrated lime is preferable to agricultural limestone because it has a higher calcium carbonate equivalent and less of it is needed to raise the soil pH to 7.2, at which the environment for clubroot spores is unfavourable.

“Hydrated lime is a little bit harder from a producer standpoint to apply, because it’s almost the consistency of icing sugar, but research has showed that it’s the most effective liming product,” she says.

“Genetic resistance maintains to be the most effective tool when managing clubroot,” says Hennig, but as she explains in the video using a graph, the combination of using a clubroot resistant cultivar, managing weeds that act as a host to clubroot, and applying hydrated lime, achieved higher yields.

“A resistant cultivar with no weed management had about the same yield as a susceptible or resistant variety that is no longer resistant to the pathotype, with the application of lime,” says Hennig. “What’s important to note is that one grouping has a higher spore density as the other and even though they’re yielding the same, we need to be very aware that there can be a lot going in the soil that we’re not seeing.”

Hennig’s advice is to be proactive, scouting for clubroot by pulling up plants, and managing spore load ensures that clubroot can continue to be managed effectively.

“Clubroot can be a very manageable disease, and it doesn’t need to have a negative stigma attached to it, we just have to make the proper management strategies, and multiple management strategies, in order to get control of it and continue to grow canola without clubroot impacting those yields,” says Hennig.

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