Mildew and Blight!
It is to be expected this time of year in most veggie gardens that you will experience powdery mildew on many of your plants. I find it most common on the curcurbit family, courgettes, cucumbers and pumpkins. It is not nice to look at but it doesn't usually effect the vegetables which are coming to the end of their season anyway. Early in the season you can inhibit the start of powdery mildew by making your own home made spray from 1tsp baking soda, 1 quart water, few drops of liquid soap.