why are my courgette plants covered in mildew?

I am growing my courgettes in large containers on the patio. They are well looked after and at the moment are still producing a constant supply of fruit, but the leaves are becoming covered in mildew and the plants are beginning to look very poorly. What am I doing wrong?

In my experience courgettes and squashes always finish up with powdery mildew as the weather gets cooler and damper in late summer and the plants start to get a bit knackered.

It usually starts in the older leaves which are nearest the ground and therefore moister for longer; take any dying leaves off whether mildewed or not. This will slow the spread of existing infection and also improve the air circulation round the plant which will also help, as will trying to keep the leaves as dry as possible when watering.

Not tried the diluted milk treatment - can't quite bring myself to deliberately cause more leaf wetness but would certainly give it a go if folk out there really think it works.