Powdery Mildew

Clearly, things have been going too well for me this year (after last year's tomato blight and courgette-mosaic disaster), and it's time for a new problem! This year, my sweet peas and lupins are both suffering from that rather bothersome fungal problem of Powdery Mildew. I wasn't sure what it was, although the words popped into my head as "something that can go wrong in your garden". Here's what it looks like:

From Drop Box

I don't think I'm going to bother doing anything about it at this stage in the game, although if I did, the RHS would surely come to the rescue.