Answer: It's difficult to diagnose from your description, but your grape vines may be showing damage from the feeding of of erineum mites, or may have symptoms of Downy Mildew. When mites feed on the undersides of leaves, the upper portion of the leaf can take on a blistered look. They don't generally affect the vines, though. Downy Mildew, a fungal disease, can affect both leaves and vines. The most prominent features of this disease are lesions on leaves and stems that look yellowish to reddish-brown, eventually turning to a felt or downy looking spot. You're wise in removing affected plant parts because you're stopping the spread of the problem. For an absolute diagnosis, take a sample of the problem to your local Cooperative Extension office. You'll find friendly, helpful folks at Cornell Cooperative Extension, 246 Griffing Ave., Riverhead 11901-3086. Phone (516) 727-7850.
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