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A disease rotation can fight effectively

A field of canola sways slightly in the breeze, the bright yellow flowers papering the gently rolling land in a golden hue.
Field rotation recommended for clubroot

A field of canola sways slightly in the breeze, the bright yellow flowers papering the gently rolling land in a golden hue. But here and there the gold is less brazen and a bit patchier, and the reason for that is clubroot.

A soil-borne disease, clubroot spores can hungrily infect plants in the brassicaceae (cruciferae) family - cauliflower, broccoli, mustard, turnip, radish, and canola. It also infects certain weeds like stinkweed and shepherd’s purse, which can help the spread of the soil-infecting spores.

“Clubroot forms a gall, or a club, on the root of the plant that prevent the uptake of water and minerals, therefore slowing its growth and stunting the plant, and resulting in not-good yields,” explained Quinton Beaumont, director of agricultural services for the county. “It can stop the plant from ripening at the right time, resulting in green kernels.”

The county’s pest control program has placed the detection and prevention of clubroot fairly high in its program, and has held clubroot education sessions for the public already this year.

In 2012, the first clubroot infections in the county were discovered after root samples were brought to the county for testing.

“Three fields were found that year,” Beaumont said. “In 2013, three more fields were found - in 2013, two were fields, one was a garden. In 2014, we had nine fields.”

It doesn’t affect crops like wheat or barley, and Beaumont notes that he and his staff don’t even inspect those fields for the soil disease right now, focusing instead on fields growing mustard and canola.

The disease doesn’t move without help, Beaumont noted. Theoretically, a patch of infected soil will remain put and not grow in size. However, if the soil moves, whether it’s blown by the wind, washed downslope by water, carried on boot or tire, or even in the digestive tracts of animals, it can be deposited elsewhere. If crops or weeds are grown in infected soil, they can help generate and spread more spores.

Because of the infectious nature of the disease, staff perform random inspections of canola fields throughout the season.

“You cannot see it with the naked eye,” Beaumont said. The spores are invisible to the naked eye - a lone tablespoon of clubroot-infected soil can host up to one million spores. There’s no smell, no change in texture, and no taste to infected soil.

“The only way to positively identify (clubroot) is to get a lab test,” so throughout the season, staff take root samples and send them to the laboratory and wait for the results.

Before entering a field, though, staff take precautions to prevent the spread of any disease, including the clubroot for which they search. Staff will stand in a chlorine solution for several moments to sanitize their boots, then wear plastic booties over their feet. Once they leave the field and remove the booties, they’re disposed of and the staff stand in the chlorine bath again to kill any spores.

The precautions are necessary. Once a field is infected, spores can be present for up to 20 years.

“Clubroot is like a tick,” Beaumont said. “If you remove the host, you can remove the pest.” The spores have a half-life of four years, meaning that teaspoon of soil with a million spores will have 500,000 after four years.

“If you don’t plant canola (or any other susceptible plant) for four years, you halve the number of spores in the soil”, Beaumont said.

That’s one of the reasons why plant rotation is so important, Beaumont noted. The province of Alberta, in its clubroot management best practices, recommends a one in four cycle for planting canola, meaning that for one year, canola is planted and then for three years, a non-cruciferae crop like wheat or peas.

“There’s nothing made to help control it - yet,” Beaumont said of fungicides, herbicides and pesticides.

As of April 2007, the disease is on the provincial pest act. When farmers don’t have the disease in their soil, all the county can do is recommend best practices to the landowner when it comes to which crops are planted and weed control.

“We have the power to enter land at any reasonable hour, without permission, to inspect for pests and collect samples,” Beaumont said. “We can mitigate and manage it through various management plans.”

“I can suggest to you until I’m blue in the face you should rotate crops. Once we find clubroot in a field, you have to follow county policy,” Beaumont said. This means if a field is found infected, the county can say “You cannot plant canola here for four years.”

While the worst infections of clubroot aren’t in central Alberta. Red Deer County, Lacombe County, Camrose County, and Flagstaff County have all found clubroot infestations in addition to Stettler County, to varying degrees.

However, nearby counties Paintearth, Starland and Special Areas have remained clubroot free.

What can we do to prevent the spread and establishment of clubroot?

“Rotation, rotation, rotation, is number one,” Beaumont said. “We are suggesting a one in four year rotation. You grow canola once, and for the next three years you grow something else.”

Beaumont said that farmers should use clubroot resistant seeds when seeding susceptible crops, which will help prevent infections and the creation of more spores.

A huge piece on rate-payer’s end of things, and anyone going in and fields is the removal of soil. By cleaning equipment of soil, it can reduce the chance of spreading clubroot by 95 per cent. Knocking soil off tires and shovels, spraying equipment down with a two per cent bleach solution - soaking it well enough to remain wet for about 20 minutes.

Planting a patch of grass at the gates, where equipment can be cleaned, can help, Beaumont noted. The grass essentially acts as a pad, catching the soil and preventing it from being blown or knocked around.

Susceptible weeds and volunteer crops must be culled within three weeks, Beaumont noted. After three weeks, the plants, if infected, will begin to produce spores.

Changing the type of canola crop grown can make a difference, too.

“Switching between a Liberty Link canola and a Roundup-ready canola can help control volunteers,” Beaumont said.

Farmers who know they have clubroot-infected soil can ensure they don’t spread the disease by ensuring equipment is thoroughly cleaned between fields, and by not going back-and-forth between infected and uninfected fields, Beaumont said.

Before disinfecting, farmers should knock the soil away. The organic matter and soil will neutralize any disinfectant, making the wash worthless. By parking unnecessary vehicles on the road, and not in the field, people can reduce the amount of work needed in cleaning equipment and vehicles.

Direct seeding is a better option when it comes to seeding land, as it disturbs the soil less than conventional seeding. Making sure the seeds are clean of soil is important, too.

Avoid using straw or green feed in infected areas, as if consumed, it can survive the digestive tract of animals.

“Cattle make good broadcast seeders,” Beaumont said. However, seeding fields down with alfalfa and ranching on the land is a feasible option.

Finally, though it is extra work with the county, creating a new entrance to infected fields, so there’s direct access to the land without going through infected areas, is a good idea, Beaumont said. This involves working with the county to create new approaches to the field, but in the end, it can save 20 years of work to clean a field of the disease.