Talk about blackleg in canola has been increasing, especially with announcement of new canola varieties resistant to the disease. But is it something you need to worry about in your fields? Unfortunately, given the potential impact to your crop and farm, it’s probably wise to understand its lifecycle, how to identify it and what steps you can take to prevent and/or treat it.
Use a Multi-Method Approach to Manage Blackleg
|The lifecycle of blackleg. Credit: Canola Council of Canada|
The pathogens causing blackleg build up in soil and trash in fields, especially in tight canola rotations. Most of the blackleg infection is in the lower part of the plant, and is often left as standing stubble once the crop has been harvested. This infected stubble produces spores for three seasons (maybe more) and releases them into the air where they infect new plants. The airborne spores can travel quite a distance by wind, or, in wet conditions water can splash spores onto neighboring plants. If these spores land on pods it can result in infected seeds and lead to infected seedlings. Infected seedlings have low survival rates. While seed treatments on commercial seed can control these seedling infections, it won’t control infections to seedlings or plants by airborne spores – this is where a fungicide could come into play!
Early Fungicide Application is Best
Blackleg infection occurs throughout the season, but the earlier the infection the more likely it is to cause the characteristic cankers and yield loss that result from the disease. Infections that occur after the 6-leaf stage typically don’t result in as much yield loss as when infection occurs before. This is why earlier fungicide applications are ideal for protecting against blackleg.
Look for Leaf Lesions with Pepper-Like Spots
|An example of a leaf lesion. Credit: Canola Council of Canada|
Scouting for blackleg can be tricky. Symptoms can be seen on cotyledons, stems, leaves and pods. When seen on leaves, lesions are usually white or brown and have pycnidia (looks like pepper on the leaves).
Scouting at the 3-6 leaf stage is the best time to find these early symptoms of blackleg. The next time to scout for blackleg is at swathing. At this point you’ll be looking for cankers on stems. Cut stems at the soil level to check out the inside of the stems for black tissue to indicate disease. Ensure that you clip and assess enough stems to give you a good representation of the field. A minimum of 50 stems is a good place to start. The blackleg impact on each stem will give you the best idea of what kind of disease pressure is present in a given field.
|The blackleg impact on each stem will give you the best idea of what kind of disease pressure is present in a given field. Credit: Dr. Gary Peng, AAFC Saskatoon|
Consider a Fungicide Application
If there is high blackleg pressure in your area, you will want to take action to preserve your crop. Right now fungicides for blackleg are limited to Nexicor, Priaxor® and Quilt, although we may see more on the market soon. Recommended timing for spraying blackleg fungicide is 2-6 leaf stage or with your second herbicide pass on your canola.
Our Cargill agronomists are eager to address blackleg and any other concerns you may have in your canola. Click below to get in touch with one of us.
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