Alternaria leaf spot
The genus Alternaria is comprised of many common saprophytic (derive nutrients from dead and/or decaying organic matter) and plant pathogenic species.
Alternaria brassicicola causes black spot disease (also called dark leaf spot) on virtually every important cultivated Brassica species including broccoli, cabbage, canola, and mustard. It is of worldwide economic importance resulting occasionally in 20-50% yield reductions in crops such as canola, mustard or rape. Like other diseases caused by Alternaria species, black spot appears on the leaves as necrotic lesions, which are often described as black and sooty with chlorotic yellow halos surrounding the lesion sites.