Research has found that 50 percent of clubroot spores are gone or non-viable after a two-year break from canola
New research is changing the way farmers and industry look at clubroot.
The information is challenging conventional wisdom from when to seed in a clubroot infested field to the life cycle of the disease, said Dan Orchard, an agronomy specialist with the Canola Council of Canada.
Researchers used to believe the half life of clubroot was four years. Now, new research from Agriculture Canada in Quebec has shown 90 percent of the clubroot spores are gone, or non-viable, after a two-year break from canola, said Orchard.
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A common wheat-canola rotation is a guaranteed way to build up clubroot spores in the soil, and having a two, three or four-year break is key to breaking the clubroot cycle and allowing farmers to grow canola.
“Two years out of canola is a huge saviour from the disease,” Orchard told a recent Alberta Canola Producers Commission meeting in Camrose.
“Spore levels build up dramatically in a wheat-canola rotation.”
Even the life cycle of the disease is not well understood, and researchers are trying to understand more about the complex disease and how to control its spread through soil. The clubroot life cycle was documented in 1890.
“There is more to this disease cycle than was recorded 100 years ago,” said Orchard.
Clubroot is a soil borne disease that affects canola, mustard and other members of the cabbage family. It was first reported on broccoli, cabbage and cauliflower in home gardens near Edmonton in the 1970s. It was identified in a canola field northwest of Edmonton in 2003 and has since become a major economic concern for farmers.
Clubroot spreads by soil infested with resting spores. There are about 10 million spores in a gram of soil, which is about the size of a Smartie.
In Alberta, 1,500 fields are officially infested with clubroot, but realistically the number could be multiplied by 10, he said.
In Saskatchewan, clubroot was found in two fields in 2011 and one in 2012, but Orchard said that has more to do with a lack of surveying for the disease than a lack of clubroot.
The province surveyed 100 fields for clubroot this year, which is less than what’s conducted in a single county in Alberta.
“Leduc County surveys more fields than all of Saskatchewan.”
In Manitoba, clubroot is tested through soil rather than plants. The disease has been found in more than 80 fields, but only three or four fields have an infestation high enough to infest the plant.
Researchers developed clubroot resistant varieties of canola in 2010 that enabled farmers to once again grow canola on clubroot infested land. However, the disease had been found to have broken the resistance in one field by 2013, 16 in 2014 and 32 this year.
The most common of the 16 new strains is 5X, but there appears to be three strains of 5X. Clubroot pathotypes 3, 5 and 2 are the most common in Alberta. Pathotype 3 makes up 90 percent of the pathotypes in Alberta.
Researchers have found new canola lines that were resistant to all the 5X strains of clubroot. The germplasm will soon be available to all crop scientists, he said.
Researchers are looking at a host of new management strategies to control clubroot, including liming, fungicide, bait crops, soil amendments and biological approaches.
The fumigant Vapam had “dramatically good control” when tested in the greenhouse but only 40 percent efficacy in the field. It also killed everything in the soil, including worms and other beneficial pests.
Fumigation wouldn’t work on a large scale, but it might be an option for pipeline construction or other small areas of a field where introducing clubroot into a field is a concern, he said.
Fumigation may also be useful in field entrances where 90 percent of clubroot spores are discovered.
“When someone finds clubroot, it is at the entrance.”
Canola specialists used to advise seeding clubroot-infested soil last to prevent spreading the spores to uninfected fields. New research has shown clubroot spores become active when the soil temperature reaches 15 C and most active when the soil is 20 C. Seeding clubroot-infested fields early before the spores are active may be a good way to limit its spread.
Adding lime to soil will keep clubroot at bay if there is little clubroot in the field but does nothing to control fields that are already infested.
Research into boron as a control for clubroot has also been examined. Boron controlled clubroot, but the amount of boron needed for control also killed the canola. However, researchers identified 10 varieties that are tolerant to boron.
“This is an opportunity for seed companies to put boron tolerant traits in our clubroot resistant varieties,” he said.
“We need a multi-prong approach to get past the disease.”
mary.macarthur@producer.com
