The Q&A Archives: Growths On Grape Leaves

Question: Occasionally I find these strange growths on the undersides of some of my grape leaves.The growths are about 1/4
inch in diameter raised like a blister but extremely solid and not soft in the least, they also sometines have a reddish tint to the top of the growth and they send out tiny tentacle like structures to the surrounding host leaf, making the growth resemble a tiny octopus. What is this and how do I deal with this?

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 Penn State University, (814) 865-2541.

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