It is powdery mildew, common in NorCal, you need to increase your ventilation and lower you humidity. You should cut out the infected leaves if you are close to harvest. They sell many products for this, and you can use baking soda, milk, and many other home remedies. It is Powder Mildew aka PM. If you can get yourself some Eagle 20, you will be golden, don't spray anything unless you have 3 weeks or more left