It could be a little downy mildew. But if that's all there is and the plant is established, it'll grow out of it.

I can sympathize. I spent the better part of two months nursing mine along under sunscreens and lost it all to aphids and white flies. I tried everything but the little buggers were just too prolific. I got one tiny pumpkin off of 6 vines. The extension office said to put a board or cardboard down on the ground at the base of the plants. The adult squash bugs will congregate there at night. Then you can pick-up the board in the morning an squash all the adults. Then spray the underside of the leaves with Malathion to catch the hatching eggs. If you have a large number of vines like I did, itÂs very time consuming and you have to hit every leaf. I had absolutely no problems with my spaghetti squash, but the pumpkins were a different story. Good Luck.

Looks like Powdery Mildew. In order to prevent it the entire plant should be sprayed weekly begining in mid June with a some sort of fungicide, organic or other. 1000 pounds is not easily reached.

Baking soda makes an inexpensive control for powdery mildew on plants. The baking soda fungicide is mostly effective as a preventative, offering only minimal benefits after your plants have become infected. Weekly spraying of susceptible plants during humid or damp weather can greatly reduce the incidence of powdery mildew in your garden. To control powdery mildew on plants, mix together: 1 tablespoon of baking soda 1/2 teaspoon of liquid soap 1 gallon of water Do not store unused mixture. While this recipe has been known to be effective, it can burn the leaves of some plants. It is recommended that you water your infected plants well a couple of days before applying this mixture, and dont apply it in full sun. or you can buy the more expensive fungicide. this late in the season give it a try.