it's possible that you have Grape Erineum Gall Mites feeding on the undersides of your grape leaves. Check the undersides of the affected leaves for a whitish dense growth. this is indicative of these kinds of mites.
if these are mites, your grape leaves do not appear to have a severe infestation if the picture enclosed is the worst of the problem. Therefore It should not be necessary to treat for them. If "puckering" of the leaf surface develops and the infestation appears to be getting worse, you may need to apply a miticide.