The Q&A Archives: Grape Problems

Question: I have 4 varieties of seedless grapes on my arbor...the problem is, I have GALLS on the leaves each summer and in turn, the grapes come out looking like little BB's...what can I do? I have been advised to cut down and dig out the vines, (they're over 25 years old), and start over, someone else told me to spray the leaves with cooking spray (PAM).

Answer: Cutting down the vines seems extreme and spraying the leaves with vegetable oil doesn't sound too effective. 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.

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