We get problems with powdery mildew on peas, courgettes, cucumbers etc this seems to happen (particularly with peas later in the season. I have discovered a simple cure - a dilute solution of baking soda (about a teaspoon to a pint of water) sprayed on the leaves kills it off and seems to act as a deterrent. We have courgette plants starting to flower in the poly tunnel (a late sowing experiment!) and they were coming down with mildew. This treatment has stopped it in its tracks.
We had great fun harvesting our walnuts this weekend (no squirrel this year?) and had a bumper crop of 9 kilos.