The soil-borne disease that caused yield losses in Manitoba canola crops this year was also found in Saskatchewan fields
A soil-borne disease first detected in Manitoba in 2014 caused yield losses in 2020 canola crops.
Verticillium stripe appears to be making its way west, as some fields in Saskatchewan showed symptoms this summer as well.
Justine Cornelsen, agronomy specialist at the Canola Council of Canada, said verticillium longisporum is different from another species, verticillium dahliae, which affects potatoes and sunflowers.
It is found in Europe and Australia and, because it was detected so recently, very little Canadian research has been completed. Most studies are only in year two or three of five-year projects, she said.
When it was first found, it was considered verticillium wilt but the name was changed because it is a stem-striping disease, Cornelsen said.
In 2015, a survey found it in six provinces, but this past year saw the most significant losses in hot, dry weather.
“Producers were claiming yield losses,” Cornelsen said during a webinar. “We were seeing crops that were lodging, or very fragile, brittle, starting to shatter out.”
The pathogen causes canola stems to shred and decompose. Taken up by the roots, it moves up into the stem and plugs up the xylem later in the growing season. The stems start to turn grey or black and it will eventually kill the whole plant.
“This is a soil-borne fungi similar to that of clubroot,” Cornelsen said. “This is something that is going to move anytime that soil is transferred.”
More alarming is that the microsclerotia are hardy and will last in the soil for 10 to 15 years, she said.
In Europe, research based on winter types of canola or oilseed rape found losses of 10-50 percent in Germany and Sweden. Newer research on spring oilseed rape has found inconsistent or insignificant yield loss, Cornelsen said.
Quality seems to be unchanged.
“The oil content, the composition of proteins, fatty acids, all of those remain unaffected,” she said.
Environmental conditions can determine how fast the pathogen moves into the stem. There hasn’t been much work done on this in Canada, either, but Cornelsen said it grows relatively slowly in cool soil temperatures below 12 C. As the temperature increases so will the disease.
Once the soil temperature is above 15 C, especially right before flowering, the pathogen will do well.
Farmers should look for dieback, or early senescence, and dead plants. While verticillium stripe will resemble other diseases, such as sclerotinia, stem senescence is the major indicator. Half of the stem, lengthwise, will remain healthy and green and the other half will be grey to black.
When looking at the stem crosswise, it will be grey or black in a sort of starburst pattern, compared to blackleg’s predominant black spots.
Cornelsen said alternaria can show a greyish hue as well. Peeling back the outer stem wall of the plant will reveal the microsclerotia and allow for a correct diagnosis. The microsclerotia will be tiny and uniform, rather than in patches.
Another indicator is the plants will snap when pulled out of the ground.
She said treatment options are limited.
“We don’t have any preventive or curative controls from fungicide. We don’t have a foliar or seed treatment available.”
There is no good information yet on whether any varieties are resistant.
Increasing rotations, as with clubroot, will help, but the populations will remain the soil.
“This is where looking at other options, looking at equipment sanitation, creating your on-farm biosecurity plan, play a role,” she said.
Cornelsen said following the management practices for clubroot will help keep verticillium stripe at bay.
She said industry is continuing to monitor the spread and level of infection. So far, between 20 and 30 percent of samples in Manitoba this year showed symptoms. Some fields in Saskatchewan may have been infected but there is no sign of the disease yet in Alberta.
Cornelsen said canola growers in the Swan River valley noticed premature ripening, dropped pods and plants that were difficult to harvest because the stems were brittle.
“Combines are going to be a really high risk area for spreading this particular pathogen because you’re cutting the stems where all the microsclerotia are forming,” she said. “From there you’re opening up the stems and allowing the microsclerotia to coat the combine and blow in the wind.”
A couple of research projects underway include one at the University of Manitoba that is funded by the canola cluster under the Canadian Agricultural Partnership and looking at the cause of verticillium stripe.
Another, at Agriculture Canada in Saskatoon, is examining genetics and genomics with a view to establishing resistance.
Preliminary data has found that plants infected later are colonized by the microsclerotia more quickly.
Asked if the disease could be worse if canola is left to straight cut, Cornelsen said typically a farmer goes into the crop earlier to swath so that would keep the pathogen from moving further up the plant.
More information can be found on the canola council’s website at www.canolacouncil.org/?s=verticillium.x4.