Think of clubroot like a grass fire. The best way to contain the spread of clubroot is to work diligently outside the hot zone using whatever tools available to keep the “fire” from spreading to your farm.
Seeding clubroot-resistant (CR) varieties is a good early action. Consider any variety with some source of clubroot resistance in combination with prevention measures including equipment sanitation, host weed management and minimal tillage. If clubroot sparks happen to land on a field, tillage spreads those sparks farther and faster.
Growing CR varieties in low- or no-clubroot communities does not increase the selection pressure for clubroot pathotypes that will overcome that resistance. If growers wait for clubroot to show up before choosing CR varieties, the selection pressure for resistance breakdown is literally millions of times higher than if growers begin using CR varieties before the disease shows up. (See “The math of risk” in this article.) CR varieties are an ideal choice for those fields without clubroot that are situated in or near areas known to have clubroot.
In Manitoba, Saskatchewan and Peace and southern regions in Alberta, growers can default to CR varieties to keep the clubroot risk lower. Going early with a CR variety is no disadvantage from a clubroot management perspective. Look at complete agronomic package when choosing a variety.
Growers who (1) haven’t observed clubroot on their farm, (2) diligently test soils, (3) have restricted access to their fields and (4) scout crops for clubroot galls, may not need a CR variety.
Variety choice inside the fire zone. Resistant varieties suppressed the fire for many growers, allowing them to continue to grow canola in fields known to have clubroot. However, flare ups have been spotted and the risk of full-blown fire has returned. At least 10 new pathotypes have been discovered in fields in central Alberta. While varieties with improved resistance to 5x may provide a benefit, this resistance may not work on all new pathotypes. Infection from the other virulent pathotypes could still occur.
Growers have more choice when it comes to clubroot resistant varieties as they make their seed selections for 2016. Some new varieties (with resistance traits discovered through grower-funded research) do show improved performance in the presence of new pathotypes, such as some of the 5x pathotypes.
That is why crop rotation remains important in fields where clubroot has infected canola plants. Rotation can help to smother a fire. If clubroot symptoms are observed in a field planted to a resistant variety, the responsible option is to not grow canola (any variety) for at least three years once clubroot is established. This will help to preserve and protect new resistance genetics becoming available and hopefully keep spore levels down at a manageable level.
In fields that have produced two or more clubroot-resistant canola crops on infested land, longer rotation may be required to keep spore levels down to prevent significant losses.
Here is the list of clubroot-resistant varieties, as updated on clubroot.ca.
Bayer CropScience: L135C, L241C
Brett Young: 6056CR, 6076CR (interim registration)
Cargill: V12-3 (interim registration)
CPS: PV 580 GC (interim registration)
Dow AgroSciences: 2020CL (contract registration), 1020 RR
Monsanto/Dekalb: 74-54 RR
Pioneer Hi-Bred/Dupont: 45H29, 45H33, D3155C, 45CS40 (interim registration)
Listen to a podcast on clubroot from Canola Discovery Forum
Hold back the economic clap from clubroot
Clubroot update: Manitoba cases, R varieties
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