Alternaria Black Spot

Alternaria black spot, a plant disease caused by fungal pathogens, is present in most years across the prairies. However, moisture and temperature play a significant role in its severity. Early lodging and cooler, wet temperatures can lead to outbreaks.

This disease can affect canola plants and result in mold and a dusty, dark grey to black color on mature plants. When found on canola pods, Alternaria black spot can increase the green seed count, cause premature pod shattering, and shriveled seeds.

Management options include extended rotations that don’t include canola every second year. The Canola Council has conducted research and found that it takes 3-4 years for canola stubble to decompose, which Alternaria can overwinter in. Tillage is another option, as buried stubble prevents Alternaria black spot spores from being released. Applying a fungicide at 95% flowering could also be a possibility. If you do have Alternaria black spot in your canola crop this year, you could consider swathing early to minimize losses from shattering.