Powder mildew got my peas, squash (including zucchini) and cukes. Didn't bother my beans. I used some horticultural oil (jojoba) at first sign that slowed it down, but didn't eliminate it. The mildew finally won late this summer. It didn't kill the plants but drastically reduced their yeilds.
The spores stick around and can come back next year. I will be looking to plant resistant varieties for a couple years in an attempt to reduce the resident spores.