Mildew/Leaf mould

I get powdery mildew every year on my courgettes and just ignore it

Can't remember what causes it (dry conditions?), sorry - but others will be along when they've got up 

Leaf mould is what you make from rotting down leaves over a year or 3; it becomes another form of organic matter used in the garden or pots.

After years of trying to combat mildew on courgette leaves I now just cut those leaves off, as it tends to be the big old ones that are not doing much for the plant anyway.

Then give the plants a feed and keep up with watering well