I don't grow pumpkin but I grow zucchini and summer squashes. All in the same family with the same mildew problems. Usually I just leave the mildew as I have found once it starts it progresses very rapidly and no use fighting it. Once it gets too bad and any fruits have been picked, I just pull the plants. I always bag them for the yard waste pickup as I never want to compost squash what with the problems between those mildewy leaves the the Squash Vine Borers.
