Septoria leaf spot is a severe fungal disease caused by Septoria lycopersici and often affects tomatoes and potatoes. The spots are circular with dark brown margins, gray centers, and small black fruiting structures.
A diagnostic feature of this disease is the presence of many dark-brown, pimple-like structures called pycnidia (fruiting bodies of the fungus) that are readily visible in the tan centers of the spots. When spots are numerous, affected leaves turn yellow and eventually shrivel up, brown, and drop off.
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