Forty-eight Manitoba fields are confirmed to have clubroot spores, a soil-borne, potentially destructive canola disease, up from 13, according to the latest clubroot survey update from Manitoba Agriculture, Food and Rural Development (MAFRD).
The results were expected and officials predict they’ll find even more with additional sampling. The good news is the number of clubroot spores in most infected fields is low — under 80,000 per gram of soil — meaning longer canola rotations, sanitation and resistant varieties can keep the disease in check, MAFRD plant pathologist Holly Derksen said in an interview June 5.
“We don’t want people to think it’s spreading based on this map compared to our previous map,” she said. “It’s just now we’ve really upped our sampling load. We’re figuring out where it’s now present. It’s not necessarily spreading, we’re just trying to get a better representation of where it’s present across the province.”
In Alberta, where clubroot was first detected in Western Canada in 2003, it’s not unusual to find a billion spores per gram of soil.
“We are nowhere near the situation in Alberta,” Derksen said. “That was the whole purpose of this project — to find it at these low concentrations and be able to give growers the information so they can manage it long before it gets to those really high levels.”
Manitoba farmers needn’t be alarmed by the latest results, but they should pay attention, she said. And they should test every field that has grown canola to know whether clubroot is present and to what extent.
“Our message is get tested,” Derksen said. “Just because your RM has been tested, or later your township-range has been tested, it doesn’t necessarily give you any indication of what’s happening on your own farm, because it is so variable out there.
“The half-life of (clubroot) spores is four years so with a four-year (canola) rotation you cut the concentration in half. If a field is already quite low you could see a drop from a yellow (1,001 to 10,000 spores per gram of soil) to a green (zero to 1,000).”
Since clubroot spores spread with soil, cleaning farm equipment can help reduce its spread.
There are also clubroot-resistant canolas, but in Alberta some of those varieties are no longer resistant.
Manitoba’s clubroot update is based on soil samples taken between 2009 and 2014, representing fewer than five per cent of Manitoba’s farms, Derksen said. A grid sampling program underway now could see at least one field sampled in every township-range in agro-Manitoba by freeze-up followed by an updated map this winter thanks to funding through Growing Forward 2, the Manitoba Canola Growers Association and MAFRD. The results will provide a baseline by which to measure how well Manitoba farmers are doing in battling clubroot.
Last year in Manitoba there were 13 confirmed fields with clubroot spores in 10 rural municipalities (RMs). Eleven cases were based on soil tests, with no visible symptoms in canola plants. In the two cases where plants were infected, the symptoms were minor.
The latest results show 18 RMs have not been tested. The sampled RMs have had at least one field sampled.
The number of cases where more than 80,000 clubroot spores per gram of soil was found or canola plants showed clubroot symptoms, is unchanged at two, Derksen said.
The total number of RMs confirmed to have at least one field with clubroot spores is difficult to say because the green-coloured RMs on the survey map have anywhere from zero to 1,000 clubroot spores from the tested fields, she said.
There are 15 yellow RMs (1,001 to 10,000 spores), three orange (10,001 to 80,000) and two red (over 80,000).
“To me green is not alarming but it still might be present there, but it could be at really low levels,” Derksen said. “That’s good information for the individual grower but does that mean the entire RM has to be put on alarm? Probably not.”
MAFRD is encouraging farmers to get their fields tested. The grid sampling project is still looking for farmers to volunteer fields for testing. Those chosen will get the test for free, however, only fields in untested townships will be selected.
The test, which can measure very small levels of the microscopic, soil-borne plant pathogen called Plasmodiophora brassicae, normally costs $125. However, farmers who participate in a biosecurity plan can get rebates cutting the cost to $25.
Interested farmers can get more details at The Pest Surveillance Initiative: Clubroot Project website.