Second picture, closer up.

I really can't tell from your photos, but offhand I'd guess powdery mildew. You can take some leaf loss from that especially this late in the season.

http://extension.arizona.edu/yuma

http://extension.arizona.edu/yuma-master-gardener

Give them a call and find out when they have either a diagnostic clinic scheduled or if a plant pathologist is available for you to drop by. When you do visit, take a FRESH cutting of the affected vine IMMEDIATELY before you go in and SEAL it in a ziplock bag so disease/pest won't spread.

Leafcutters are good. Yuma heat is harsh. Dry too. What sort of grapes are they, and might they be just stressed? What happened last year?

But like Fascist_Nation said, it sure does smell like powdery mildew.

The 'stippling' on the leaves is most likely caused by a leafhopper. It's piercing mouthpart sips fluid from cells in the leaves leaving them colorless and dry.

Leafhoppers are tiny cicada-looking insects and have the curious habit of moving away from you either by circling a stem or leaf. They don't like shade so sometimes shadecloth can help. The U of A Extension resources mentioned earler are good ones.

Here is a link that might be useful: Grape leafhoppers

I looked at the leaves closer. I saw small gray looking insects. He does indeed have leaf hoppers. Thanks for that link. I will show this to him.