Author: Natalie Hoidal, UMN Extension horticulture educator Alternaria (black / brown leaf spot) in Cole crops - Rice and Chisago counties We've seen Alternaria leaf spot showing up on cole crops on a few different farms this week. Alternaria leaf spot is caused by three different strains of the Alternaria fungus: Alternaria brassicicola, A. brassicae, and A. raphani. It can be identified by the target-like appearance of spots on the leaves, forming concentric rings. Leaf spots tend to appear first on the lower leaves, and will often break open and fall out. If you're seeing Alternaria for the first time in your fields, the disease likely came on infected seed. Alternaria leaf spot on a broccoli leaf. Photo: Andrew Hanson-Pierre More information on Alternaria. For conventional growers, the Midwest Vegetable Production Guide contains a list of effective fungicides. For organic growers, options are limited, with organic fungicide products showing ...