Blackleg is a disease in canola mainly caused by the fungus Leptosphaeria maculans. It’s a serious disease that affect canola plants in the seedling stage by attaching to the stems and working up the stem as it grows, inhibiting the movement of water and nutrients within the plant. It can cause upwards of 50% yield reduction in severe cases. Blackleg was first spotted in western Canada in 1975 in north-east Saskatchewan.
Chris Manchur is an agronomy specialist with the Canola Council of Canada, and he explains not only what blackleg is, but how it affects canola crops and how producers can combat it.
“Blackleg, otherwise known as Leptosphaeria maculans, is a pathogen that causes a significant amount of yield loss in some extreme cases (in canola), it's a stem canker disease that essentially restricts the canola plants from obtaining all those nutrients and water. This is a stubble-borne disease and so it will carry over from previous years. If you're growing canola and when these infected stubbles have the right conditions in the spring, you'll start to see ascospores released and will infect throughout the earlier stages of the plant.”
This infection in the early spring, ends up translating to yield losses later on in the year as the canola plant can’t effectively transfer water and nutrients up the stem towards the leaves and chokes the plant out. This is nothing new to canola growers, as Manchur mentions, blackleg has been around a long time.
“Blackleg’s been with us for many years, decades even. In the past, we've had a lot of tools in our toolbox to help manage this disease but of course, it's always an arms race with some pathogens and right now blackleg can be pretty common across the prairies. The best time to really start off when we're talking about Black Lake is in my opinion, right at the canola harvest stage, because this is when you're starting to find the symptoms and starting to find the stubble that's actually infected."
Once growers have identified blackleg in their canola, they can then launch the proper management practices to help control the infection and spread. Manchur explains, it starts with the genetics of the seed in the spring, and goes all the way into fungicide sprays in the summer.
“There are many different approaches we can take to manage blackleg. One of the top ones that we want to consider is genetic resistance. This is something that's going to be inherent in our canola cultivars, and there's two different approaches you can look at. Adult plant resistance or you can look at R gene resistance. We want to take a look at a layered approach in terms of managing blackleg and another couple layers is taking a look at seed treatments or fungicides. Right now, there are a couple different seed treatments available that actually provide good resistance in protecting canola seedlings in that critical period of infection that happens early on. In very certain cases where your risk is high, where you have the right environmental conditions, you may want to choose a foliar fungicide.”
Canola growers are encouraged to continuously monitor and scout their canola fields throughout the growing year and look for increased blackleg pressure. Also, producers can send their canola seed to SaskOilseeds for free testing to ensure the genetic resistance against blackleg is present before it’s in the ground.
For more information regarding blackleg management in canola, visit the Canola Council of Canada’s website, and talk to your local agronomist to help snap the blackleg.
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