Disease Watch An update on incidence, severity and best management practices. Blackleg and Clubroot in Canola 30 www.seed.ab.ca | Advancing Seed in Alberta BLACKLEG and clubroot are both serious diseases that are growing in severity across Alberta, but with proper and diligent management by all farmers, they can be effectively controlled. Blackleg Blackleg is a fungal canker or dry rot that results in stem girdling and lodging. The disease has been present in canola fields since the 1980s. Today, the availability and use of canola cultivars with resistance to blackleg has helped to avoid significant damage, notes Michael Harding, a research scientist with Alberta Agriculture and Forestry (AAF). However, it is still very common to see blackleg in canola crops. Harding and his colleagues have undertaken recent surveys for blackleg (and stem rot) on Alberta canola. In 2016, they found that of 480 canola fields, 432 of them had blackleg symptoms. Indeed, Harding states “the prevalence of blackleg in Alberta has been measured at 55 to 99 per cent in the six surveys conducted over the past eight years. Prevalence was slightly lower in 2017 compared with 2016, as it was a relatively dry year in comparison.” Long-term survey trends show the pathogen to be present throughout the province, and Harding does not believe any area or farm should consider itself “blackleg free.” Some fields experience little to no loss due to blackleg while others may have significant disease pressure, and he says economic loss experienced by individual farms depends on their location in the province, local weather and field history, as well as cropping and disease management practices. “Blackleg is always a risk for canola producers and blackleg management practices should be proactive,” Harding Blackleg overwinters on infected stubble (old cankers). Photo courtesy Michael Harding, AAF says. “Crop rotation (one host crop every four years) is a very effective way to keep disease pressure from building. The pathogen does not survive in soil without a host. So, once the canola residues are decomposed, there is little to no risk of economically-damaging blackleg pressure originating within that field.” Harding also notes that genetic resistance in the MR- and R-rated canola cultivars is keeping disease severity very low in most fields, as was seen in the survey data. However, Ralph Lange Team Lead Crop Pathology and Molecular Biology at InnoTech Alberta, notes there are now yearly cases of severe loss in cultivars labelled “resistant,” a significant change from the 1990s and 2000s that indicates the pathogen is adapting. Lange says there are about eight different blackleg strains in Western Canada, and in Alberta, about 80 per cent of all isolates belong to just three strains. Severe clubroot pulled from infested soil (note wilting of plants in the background). Photo courtesy S.E. Strelkov, U of A