The Q&A Archives: Galls On Grape Leaves

Question: I am plagued by "Galls". I have been told "Cut the vines down and dig them out and throw them away and start over"/ They are little "bumps" on the underside of the leaves that cause the leaves to curl up, and the grapes look like little "bb's". I have been told that there is no cure for galls, that the insect is in the bark of the old vines, and that they lay their eggs in the leaves......these vines are over 30 years old, and are seedless grapes that were once great. any help is appreciated

Answer: Based on the symptoms you describe, the grape vines may have a fungal disease called Downey mildew. This caused by the fungus Plasmapara viticola and is common in grape growing areas of the world with high humidity during the growing season. Downey Mildew is first observed as small, pale yellow to reddish spots with indefinite borders on the upper leaf surface with white downy growth on the lower surface. Infected leaves are killed, turn brown and may fall. Young infected shoots and cluster stems may curl, distort, show thickening of the infected tissue and may be covered with a whitish fungal mass. Infected berries turn brown and eventually shrivel. Infective spores are produced during rainy periods if temperatures are above 50F and infections are triggered by warm, humid nights followed by rain.

Limited testing has shown copper fungicides to reduce infections.

Mites can cause similar symptoms on leaves, but their feeding doesn't generally cause the grapes to be deformed.

You might want to take a sample of the problem to your local Cooperative Extension office for positive identification and control measures. (330-533-2424)

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