Agronomy Geeks West — Ep. 21: Defining "Intermediate Resistance" to Clubroot, and Why a Resistant Variety Can't Replace a Longer Rotation

Crop rotation remains the most powerful tool in the fight against clubroot disease in Western Canadian canola fields, even with new resistant varieties being brought to market.

As part of this episode of the Agronomy Geeks West podcast, host Lyndsey Smith caught up with Dr. Stephen Strelkov of the University of Alberta. His work documenting the strains of clubroot that are present on the Prairies led to the finding of the new 5X clubroot pathotype near Edmonton in 2013.

Strelkov discusses the different clubroot races and how clubroot ratings differ from labels used to describe a variety’s reaction to blackleg, for example. Until recently, canola varieties were simply labelled as ‘resistant’ or ‘susceptible’ to clubroot, but the term ‘intermediate reaction’ has been added to the mix recently. An intermediate reaction means a variety had more than 30% infection, but less than 70%. A variety with less than 30% would be resistant; a variety with more than 70% infection would be considered susceptible.

Also joining Lyndsey is Murray Hartman, oilseed specialist with Alberta Agriculture, to talk about the 1-in-4 rule of thumb and how choosing a resistant variety cannot take the place of a longer crop rotation in managing canola diseases, such as clubroot and the newest one — verticillium wilt.

So what does an ‘intermediate reaction’ to clubroot mean? How much confidence should we place in resistant varieties? Despite dating back several decades, does the 1-in-4 year recommendation for canola still stand up? What’s the cost of tighter rotations?

Find out in the latest Agronomy Geeks podcast:

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