Clubroot has been detected in 13 Manitoba fields since 2009, but all have been mild infections, says Anastasia Kubinec, oilseed specialist with Manitoba Agriculture, Food and Rural Development (MAFRD).
“What we’re finding in Manitoba right now is clubroot at very low levels,” Kubinec told the Westman Crop Talk webinar Aug. 20.
MAFRD released a map Aug. 14 showing the 10 rural municipalities where clubroot, a potentially devastating soil-borne canola disease, has been detected (see map at bottom).
But what the map doesn’t point out is that 11 of the 13 cases are based on soil samples, not visible symptoms in a canola crop, Kubinec said.
“It has been only two fields where we have found symptoms in the field and those symptoms were extremely minor,” she said.
“What we are finding in the field pretty much looks like a little pimple on the root of the canola plant. It’s very minor. In one case we actually tested a plant three times to make sure that it was positive.”
That’s in sharp contrast to the new infections found in Alberta and Saskatchewan from visible symptoms in canola fields.
Canola plants with severe clubroot infections die prematurely because large galls form on the roots preventing water and nutrient uptake.
Early detection is key to managing clubroot and swathing is a good time to be on the lookout for patches of prematurely ripened canola plants, which could be infected with clubroot. Other diseases, including blackleg and sclerotinia, could also cause such patches.
Farmers should carefully dig up suspicious canola plants and examine the roots for clubroot galls. If a farmer suspects a clubroot infection he or she should contact the local MAFRD office, Kubinec said.
Less than two per cent of Manitoba fields have been soil tested for clubroot spores so MAFRD recommends farmers assume clubroot is within 50 km of their farm. However, farmers in the 10 rural municipalities where the disease has been found should consider the disease to be closer yet, Kubinec said. Farmers in those areas should be asking service providers to clean their equipment before entering a field and farmers should also clean their equipment between fields.
Instead of waiting for symptoms to show up in their canola, farmers are advised to have soil samples tested. Anything with 100 clubroot spores or more per gram of soil is considered clubroot positive, Kubinec said.
Since clubroot is not a regulated pest in Manitoba, as it is in Alberta and Saskatchewan, the specific location of infected fields here remains confidential and is only reported as an infection in a specific municipality, she said.
Discovering the pathogen at low levels allows farmers to take action to prevent spores from building to the point where crop yields are reduced. Remedial steps include growing canola less frequently on infected land, controlling canola volunteers and other plants and weeds in the brassica family such as camelina, cabbage, rutabagas, wild mustard, shepherd’s purse and stinkweed. The longer those plants and weeds are absent from an infected field, the more clubroot spores will die, reducing the risk to subsequent canola crops, Kubinec said.
Other mitigation tools include growing clubroot-resistant canola varieties and cleaning equipment before moving between fields.
To keep clubroot-resistant varieties useful, farmers should not grow canola on infected land anymore than once in three years for fear of a breakdown in the resistance, Kubinec said.
The clubroot map is just a “snapshot in time,” and more positive cases will be discovered, Kubinec said.
“On average we’ve been finding about three to five fields per year that have popped up as clubroot positive,” she said.
In comparison, Alberta is seeing around 100 new fields infected annually and has 1,400 infected fields, she said. And both Alberta and Saskatchewan base infections on visual symptoms in canola.
When collecting soil for a clubroot test, Kubinec suggests farmers take samples at field entrances. This is where contaminated soil can fall off machinery.
Collect a trowelful of soil in a “W” pattern at five points every 10 feet and place the soil in a bag. Leave the bag open to dry and then send the soil to a laboratory for testing. Several provide the service, including Discovery Seed Labs in Saskatoon and 20/20 Seed Labs and BioVision Seed Labs, both in Alberta.
This fall Manitoba’s new Plant Surveillance Lab, which is partly funded by the Manitoba Canola Growers Association, will open and will also do clubroot soil tests.
Farmers who have attended an MAFRD biosecurity workshop are also eligible for a rebate on the cost of their clubroot soil tests, Kubinec said.
Earlier this month what appears to be a severe case of clubroot was found near Langdon, North Dakota, in Cavalier Country just south of Darlingford, Man.
Clubroot was first discovered to be damaging canola crops in the Edmonton area about 10 years ago and has been advancing by about 25 kms a year.
Clubroot spores can persist in the soil for 20 years.
In 2012, clubroot DNA was confirmed in two Manitoba fields sampled in 2011.
MAFRD reported in 2013 plants from two unrelated fields showed symptoms of clubroot galls on their roots and tested positive for clubroot DNA.