This is most likely grape berry moth. You should be able to see small light brown to purplish worms in some of these fruit. Insecticides should start when the berries are the size of small peas. Typically two applications, 10-days apart, are made to control the first generation. Sprays (two applications, approx 10 days apart) for the second generation should be timed for the veraison (berry color change) stage of development. General insecticides for fruit should work for grape berry moth.
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