Grape leaf disease
(This is a crosspost from the Garden Clinic in case I can't get an answer there.)
I live in the Pacific NW where we have rainy springs. I have 4 mature grape vines, all of different cultivars, and they grow together on a large grape arbor. I noticed that one of the vines - only one -- has a weird problem with the leaves. The leaves look normal on top and have normal color, except many of them have large raised bumps. When you turn these leaves over, there are spots of a whitish, velvety coating that does not rub off, and these spots correspond with where the bumps are. Below are photos of a typical leaf. I'd like to know what this is and what I should do about it. Thanks.