Economic Impact Alternaria affects B. rapa varieties more severely than B. napus varieties. Although B. napus varieties are not immune to the disease, the waxy coating on B. napus plant surfaces limits the severity of the disease. In B. napus, Alternaria will cause pod shattering and a decrease in seed quality. The effects in B. rapa are much more severe. Premature ripening and decreased seed size are often the result.
Alternaria infection can also cause pod shatter and increased green seed count.
This is similar to the losses attributed to Blackleg, Sclerotinia and Root Maggots. However, little is done to combat the Alternaria problem. A rotation of at least three years between canola crops is suggested. Managing the rotation of nearby fields, although difficult, can also reduce the level of airborne spores. Currently, there are no fungicides registered for Alternaria control in Western Canada.