Craig said:
What causes the white mildew on the leaves and next year how can I
stop it.

It's associated with:
cool, damp nights + heavy fruit load + other stresses (pests, nutritional).

You can slow it down, but I'm pretty much convinced you can't stop it.
Eventually the vines become senescent and succumb. *Early*
outbreaks are the ones that hurt fruit yeild and quality.

Too much nitrogen makes it worse. Adding potash and micronutrients
helps. (Seaweed spray is good.)

The best 'cure' (if the powdery mildew is consistantly early and
rampant in your garden) is to use a combination of baking soda and
oil spray.

See: http://attra.ncat.org/attra-pub/bakingsoda.html

(My neighbor's squash begins to show signs of powdery mildew weeks
before mine eventually does.)

--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)