However, now is not the time to stop thinking about inputs as there are several diseases that rob yield through the growing season. Although Sclerotinia and Blackleg are usually at the top of the list, Alternaria has been a severe problem in several areas in the last few years. All above ground plant parts are susceptible to this disease. It can appear in the spring on seedlings as dark spots on the cotyledons and leaves, but is more commonly found on pods near plant maturity, where it appears as small gray to black lesions. The fungus overwinters on crop residue, and any related Cruciferous weed species.
Spores are easily windborne and can travel great distances throughout the growing season.
Heavy dews during the period of maturation favour severe infection. 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.