That's iron deficiency. On calcareous soil being too wet can cause that. Check your irrigation system.

They'll do better with infrequent deep watering rather than some every day or two. Try once a week.

If once a week is where you're at then apply one of the iron products.

My grapes have done that before and like fruitnut said it is iron. I use ironite. To make a quick application I add 1/2 cup of the stuff to a 5gal. bucket of water, let sit over night, stir and pour around the drip line. You might want to pull the rock of their roots so you can keep an eye on the soil for watering, also you could be cooking the small roots, rocks are hot. Don't get the leaves wet when watering, try keeping those dry.