alternaria leaf spot of cole crops
Alternaria leaf spot-Lesions of Alternaria leaf spot on cole crops are typically round with a concentric ring structure. I have not found this disease to be very important on crops in the field in most years. But it can be devastating in transplant greenhouses.
Figure 1. Alternaria leaf spot lesion on a broccoli transplant. 
Figure 2. Alternaria leaf spot lesions of several different sizes can be observed. 
Figure 3. The roughly round area of diseased broccoli transplants observed here represents a focus of disease. Alternaria leaf spot probably started on a transplant in the center of this area and spread to surrounding seedlings. 
Figure 4. Alternaria leaf spot lesions on a mature broccoli leaf. 
Figure 5. Alternaria leaf spot on kale.