I've been having some success with this one. Its not perfect but it does a pretty good job so far this year.
In a 5 litre sprayer add:
Half a cup of milk for the mildews
A tablespoonful of baking powder dissolved in a cup of warm water as backup
I cup of wormwood tea to repel boarders
15 ml of Neem oil emulsified in half a cup of warm water to ward off those that are not repelled
a splosh of Canola oil also emulsified to help it all stick to the plant and to repel water.
Fill with diluted comfrey tea as a foliar feed.
Spray heavily on the undersides of everything in sight, especially tomatoes, cucurbits and brassicas, then lightly over the tops of the leaves.
Concentrating on the undersides not only gets at the moulds and critters that live there, it even helps wash off the aphids and other bugs at the same time and keeps the water out of the sun, avoiding leaf burn.
I use a solo sprayer with a wand that has a kink at the end that helps to direct the spray upwards. Do it every second day or so depending on the weather.
As I say, its not perfect, my zucchini and pumpkins got powdery mildew anyway when I had to miss a couple of days during light rain and high humidity, but I can't complain about the crop so if its working, its worth it.