Chatham County, August 2003
Diagnosis: Alternaria Blight (Alternaria zinniae)
Symptoms include large reddish brown or purple spots, at first round to oblong but becoming irregular in shape with gray or tan centers that may drop out leaving a hole. Severely affected leaves brown, dry, and become brittle. Seedlings can be killed when stems are attacked. Alternaria blight usually shows up towards the end of the cutting period for the zinnias. This is a seed-borne disease, so treating seeds can help delay the onset of symptoms. Warm and wet conditions like this summer’s never-ending rains favor disease development.
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This page last updated January 16, 2006.