Clubroot spread becomes risk in dry years

Dirt clumps on equipment are a concern in wet conditions, but spores can also move in blowing dust when soil is dry

Clubroot prefers moist soil and propagates rapidly in wet years, but in dry years spores can travel long distances in blowing soil dust.

“When you are seeding in a really dry spring like we are having, the spores are going to be moving in that dust cloud,” said Justine Cornelsen of the Canola Council of Canada.

“Any time there is dirt moving, you have the potential to move clubroot spores, whether it’s dry or wet.”

In dry years, clubroot has less potential to spread within fields because infection level and spore production are reduced.

However, once the spores have moved in the dust in a dry year, they can lie dormant in the soil for years until favourable conditions return.

“Clubroot spores are extremely hardy,” Cornelsen said.

“There are millions of them at a time, and most die off really quick, but then you have a population that lives for 20 plus years. That’s why there is the recommendation for crop rotations. If you can wait two or three years before giving that disease the host crop that it needs, you’re going to kill off most of them.”

However, there is always a population of hard-resting clubroot spores that survives and will wake up to seek young canola root hairs when the crop is planted.

Many of the recommendations on clubroot prevention are centred on wet fields so that producers know to avoid picking up big clumps of dirt and transferring them around their fields.

With dry soil, growers typically aren’t moving as much soil on their implements, but more soil moves in the wind.

Beyond spores blowing in the dust, tillage also has a large potential to transport clubroot, even in dry years.

“The scary thing with tillage is you are moving soil across your entire field,” Cornelsen said.

“Something that was just a clubroot patch, you have now disturbed that soil and have the potential to move that across the entire field. That is going to be the same as your seeding implement. As long as you can reduce the amount of soil movement, you are going to be better off.”

Growers who do not have clubroot on their fields should pull up a few plants in areas where the infection typically starts, such as entrance ways, water runways and where spring flooding occurs.

Cornelsen said clubroot symptoms are often a lot more obvious to spot in dry years.

“That is what we saw last year,” she said.

“A super dry year, plants took up the spores early on in the spring because there was a bit of soil moisture there, which got the spores moving around. Once the season progressed, those plants just took up no moisture because of the swelling of the galls, so those patches were very obvious to see.”

Growers who know they have clubroot should mark known infected areas and keep a close eye on them.

“The best thing to do is to just stay out of them. You can seed them down to something else like perennial ryegrass. Just stay out of that patch, even if it’s a wheat field,” Cornelsen said.

“A good thing for everyone to understand is that just because there isn’t canola growing in that field this year, those spores are still in the field.”

She said producers planting canola into a field where clubroot has been observed should use resistant varieties and be vigilant about monitoring because resistance is breaking down.

“You‘ve got to still be going in and scouting and pulling up plants to see how effective that resistant variety is working to the pathotypes you have in your field,” Cornelsen said.

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