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Dear Dr. Vinny,
I purchased a Pinot grape vine for my back yard, and it grew to a very large size in the last four years. This is the second year that the vine has produced grapes; however, the grapes seem to reach a small green size before small purple dots appear on the grapes and the seeds inside appear to grow much faster, bursting the grape. It seems that the grape stops growing in size once it reaches this small initial green state. Please help to answer what might be causing this. Thanks.
—Wojtek D., Portland, Ore.
While I don’t want to get into a habit of diagnosing sick grapevines here, I thought your question was intriguing and knew the right person to ask. I checked in with Remi Cohen, a Napa Valley-based vineyard consultant who is now the Director of Winemaking and Vineyards at Cliff Lede Vineyards.
Remi suggests that your vine might have measles! Grape measles, that is, also known as Esca disease. It can cause the dots you’re describing, in some cases make the leaves turn brown, and definitely can cause the grapes to crack and dry on the vine.
Grape measles are caused by a fungus, and Remi said there’s no great treatment for it. A commercial grapegrower might use lime sulfur, and there are other types of sealant you can put on any pruning wounds to try to contain the measles. Otherwise, she suggested you might want to just cut the vine back to a few buds and try to re-grow it.
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