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Dealing with a flush of clubs

Clubroot specialists across the Prairies are sharing how to slow the disease’s spread, and how to keep it down when it does arrive

It turns out 200 kilometres of forest is not an impenetrable barrier for clubroot. Canola growers in the Peace River region had crossed their fingers, but knew deep down it couldn’t hold.

“Most growers knew we weren’t living in a bubble up here,” says Gregory Sekulic, Canola Council of Canada agronomy specialist for the region. “We have a favourable environment for the disease and it was just a matter of time.”

Clubroot can survive in soils all across Western Canada, but lower pH soils of the Peace Region along with lots of host crop and a decent amount of moisture can lead to fairly intense spread of the disease when it does show up. Canola is a popular crop in the Peace Region, and moisture has been relatively abundant in the southeast Peace in particular over the past few years.

After discovery of the first confirmed field in late August, more fields were confirmed fairly soon afterward. “One was quite severe,” Sekulic says, “suggesting clubroot had probably taken hold a few years earlier.”

That field had been in canola in 2013 and 2015, both wet years in the area. “Dead patches present in the field those years would have seemed like drown-outs,” Sekulic says, “but they could have had clubroot, too.” Given the amount of clubroot in the field in 2017, they probably did.

Moving east

A surprisingly serious case of clubroot was also confirmed in northwest Saskatchewan in August. More fields were found positive in the following weeks. It was an eye-opener for a province that had, until then, just four relatively minor cases.

“While the disease situation is much more severe in Alberta at this time, clubroot is in more fields than expected in Saskatchewan and it is causing yield loss,” says CCC agronomy director Clint Jurke, who lives near Lloydminster, Sask. “But growers aren’t looking for it.”

Clubroot is soil-borne. When soil moves, microscopic clubroot spores move. The disease can arrive in a field through dirt pack on seeding and tillage tools, the wheels of sprayers, grain trucks and ATVs, and dust inside harvest and haying equipment. It can also arrive with dirt tag on common seed and with erosion.

“Movement of this pathogen is almost impossible to prevent,” Jurke says. But farmers have effective measures to slow the volume of spores moving onto their farm and, when it does arrive, to greatly reduce the movement within fields and from field to field throughout the farm. Step one is to start looking for it.

Yellowing patches are easy to see from the air and they could be clubroot, but walking into the patches to scout for galls or take soil samples will be necessary to “ground-truth” the actual presence of clubroot.
photo: Victor Manolii

How to scout

Dan Orchard tried a new way of scouting this year. The CCC agronomy specialist for central Alberta north took to the air.

From the window of a small airplane 400 feet above the fields, he and the farmer-pilot could see infected patches throughout fields. The most interesting feature was their shape.

“We noticed patterns unique to clubroot,” Orchard says. “Patches had streaks of prematurely ripening plants moving out from them.” This was the result of seeding or tillage tools moving spore-infested soil out from the original infection site, like a paintbrush spreading a yellow blob of paint over a green canvas, first one way, then the other, with the amount of yellow diminishing as the brush runs out of paint.

“You wouldn’t see that from the ground,” Orchard says.

They flew over one field near St. Paul they knew had clubroot. On an earlier ground-based visit, Orchard and the farmer had identified three spots near the road. “Flying over, we easily identified 20 more spots throughout the field,” Orchard says.

From a plane or drone, farmers and agronomists can identify potential diseased areas they may not find on foot because trudging through mature canola can be just too difficult. For those without a plane or drone, the swather can be just as good, with dead patches showing up really well among the healthy just-turning plants.

To scout, start with those plants with obvious symptoms. Dig them up and look for raisin- to plum-sized galls around or near the tap root. If the plants are dead, galls may have already decayed. These rotted galls look like brownish sawdust-like material around where the tap root would be. A DNA test could confirm clubroot. Meanwhile, healthier-looking plants beside these dead plants may also have clubroot and their galls will probably still be the fresh potato-white of a living gall.

Another scouting option is to check the weeds. Weeds are often worse in patches where plants died off prematurely due to clubroot, and some of these weeds — brassica relatives such as shepherd’s purse, for example — are also clubroot hosts. If they have galls, then clubroot is present in the field.

If fields have no diseased patches (the obvious first places to scout), then dig up the root crowns for 40 to 50 random plants near field entrances or any other high-traffic areas, such as near bin-yards, beehives or oil wells. Plants can look healthy but still have small galls that cause a buildup of clubroot spores. This could mean a more serious clubroot infestation next time canola goes on that field.

One scouting option for late fall is to collect soil from diseased patches (if GPS-marked) or field entrances for DNA analysis.

“If a grower is not looking for clubroot, then the disease will certainly become worse and spread through the farming operation,” Jurke says.

Shortly after confirmation of clubroot in the Peace, canola and disease specialists, including Sekulic, presented on clubroot and fielded questions at an information meeting in the tiny community of Guy. Over 100 people showed up, and Sekulic was impressed with their down-to-business approach to clubroot. “Their focus at the meeting was not about who to blame,” he says. “The focus was on management.”

Sekulic says that overall, farmers across the Peace are showing an impressive amount of diligence.

But he adds, “If fields with large areas of clubroot are not detected and managed, the next canola crop could face complete crop loss if a susceptible variety is grown.”

Clubroot specialists across the Prairies have explained how to slow the disease’s spread and keep it down when it does arrive. The key word from the farm management perspective is the one Sekulic used: Diligence.

Disease management without diligence is like gambling. And you’ll eventually end up with a hand full of clubs.

About the author

Contributor

Jay Whetter is communications manager for the Canola Council of Canada.

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