My grape vines appear to be dying in mid-season. They have lots of pea-sized grapes but the leaves and green vines are turning brown and show no signs of growth. What could cause this?

The reason that grapevines leaf out normally and then die has less to do with spring or summer conditions and more to do with what happened during the winter. Damage to the root system or vascular system of the vine during the winter may not manifest itself until the stress of hot weather and bearing a crop load come on.