Some disease is attacking my courgette plants. It doesn't appear to be
affecting production; at least, we still have more than we can eat. But
I'm a little worried about long-term effects: will this stuff kill the
plants before the frosts, and will it cause problems for young plants in
future years (three-bed rotation)? The younger leaves don't seem to be
affected. Is there anything I can do about it?

Photos are available at http://www.edessa.co.uk/garden/courgettes.html.
I'd appreciate any advice or information anyone has.

Rhiannon