Powdery mildew, our nemesis in S. Calif coastal areas, Tim. Some varieties are much more susceptible than other varieties. You'll need to make sure they have excellent ventilation, an open canopy and not crowded, get full sunlight, and use a regular spraying program for powdery mildew. You must institute a preventative management spraying program, just like you would do for Peach Leaf Curf with stone fruits. Also, there is a Grape Forum which can help you with the specifics.

Patty S.

Here is a link that might be useful: UC Davis: Growing Grapes in Your Back Yard

Neem or Stylet oil gets the Powdery Mildew. It is a necessity. Spray and let dry overnight. Don't spray oil on in the sun. Use a regular program. We spray our vineyard every 2-3 weeks.

Check You Tube for pruning ideas. Lots of videos there.

Suzi

Should I start this spraying now, or wait until next years growth? I didnt realize there was a grape forum. Thanks for the info.
Tim

Here is UC IPM's page on managing grapes. It is quite extensive and will show you what to do, when. I would certainly start at the beginning of your dormant season, as spraying for powdery mildew is really a preventative program, and not an after-the-fact program. Also, here's a link to Grangetto's Powerdery Mildew spraying program:
https://www.grangettos.com/assets/pest/powdery-mildew.pdf
Grangetto's is a great source of information from grape growing here in my neck of the woods. Also, you might want to try growing Jupiter grapes, as they tend to do a bit better in the coastal climates of S. Calif.

Patty S.

Here is a link that might be useful: UC IPM: Grapes