Clubroot has been found in new areas. Whether it’s new to you or a perennial problem, learn how to keep it out of your fields
Clubroot has infected three new Alberta counties, and all the counties along Highway 16 to the Saskatchewan border now have clubroot. Farmers in counties with clubroot and areas bordering those counties, are on high alert, says an agronomist.
“They should be really intensively looking for this to make sure they manage it before it gets there because it’s likely to get there some day,” says Dan Orchard, agronomy specialist with the Alberta Canola Producers Commission.
Clubroot poses several risks to farmers. Once clubroot is on the farm, containing it is difficult. Yields can drop drastically, especially if the disease isn’t detected early. Orchard says he’s seen everything from almost no loss to 100 per cent yield loss, and adds it’s hard to predict yield loss.
Though resistant varieties perform very well, clubroot limits variety selection. Currently there are only a handful of resistant varieties, Orchard points out. If new, higher yielding varieties without resistance are released, they’ll be off the table for farmers with clubroot.
“You’re risking regulatory action from your county,” Orchard adds. Crop rotation restrictions vary between counties. Some impose three to five year rotations, while a few have hit infected farms with seven year rotations. Leduc County sits down with affected farmers to develop individual management plans, but Leduc’s approach is rare.
Regular field scouting is crucial to early detection.
Since machinery is usually the culprit, field entrances are the first place to check for clubroot. Farmers can also leave suspicious patches while swathing and check these patches later.
Orchard has seen one case of wind carrying clubroot from over half a mile away to infect a new field. Areas where wind continuously dumps soil are more at risk. Farmers may want to check places where snow piles or where they’ve observed wind swirling. Another potential hotspot is downwind from bins.
Above ground symptoms can include premature ripening, wilting, yellowing, or stunted growth. Clubroot symptoms can be confused with blackleg, sclerotinia, fusarium wilt and moisture stress, so farmers should dig up plants to check for root galls.
Galls will be small when the plant is first infected, and expand as the infection progresses. Earlier in the season, the galls will be white, but as the plant dies, the galls become woody. If plants are pulled several weeks after swathing, the galls may be peat coloured and decaying. By October the galls look like wet sawdust and may even fall off when the plants are pulled out.
Hybridization nodules can be confused with clubroot galls. Nodules are dense inside, and don’t decay rapidly like clubroot galls. Clubroot galls are spongy or marbled inside.
Farmers may also want to send in soil samples from fields with high traffic areas if they’re particularly concerned about clubroot.
Prevention and management
Cleaning equipment is still the first line of defence against clubroot infestation. Knocking visible dirt off equipment, including ATVs and trucks, helps contain clubroot, other diseases, and weeds. Farmers need to gauge their own risk to decide whether to disinfect equipment. If machinery needs to move from an infected field to a clean field, or a field where the clubroot status is unknown, it may be worth washing everything well.
Controlling volunteers and weeds is also an important management practice. Stinkweed, wild mustard, and flixweed all host clubroot.
While a longer crop rotation is ideal, variety rotation also helps manage clubroot, blackleg and other diseases.
“Growing that same variety in a really short rotation repeatedly is just not a good practice. …I don’t think it turns into a disaster really quickly, but it certainly will lead to the erosion of this resistance.”
A visit to an online farming forum revealed several questions about preventing and managing clubroot.
Some farmers wrote that their high-pH soils should help prevent clubroot infections. Early research seemed to show high pH levels defended plants from aggressive clubroot infections. But Orchard says more recent research reveals soil pH doesn’t have an impact when weather factors are taken into account. Researchers have found infected plants in soils with a pH as high as 7.8.
Farmers also raised questions about unconventional rotations. For example, one farmer wondered if growing canola three years in a row, followed by a two-year break, carries the same or less clubroot risk as a canola-wheat rotation that would see canola seeded three years out of five.
Orchard has been asked these types of questions before. He says canola on canola “is the worst possible idea.” Canola on canola boosts disease risk, especially for blackleg, he explains.
“I think that neither one of those rotations is good, but you’re better off to have a break in between rather than growing canola in succession. That’s where things just get out of control.”
For more information on managing clubroot, visit www.clubroot.ca. †