Rhododendrons: I seem to have a serious "rust" problem...help!

I noticed a few weeks ago that quite a few leaves on one of my large, mature rhodos were looking rather sickly, so I took a sample to the garden centre in Victoria and was told that I had "rust" - an airborne fungus of sorts that is highly infectious. I was told to remove all the ailing leaves (do not compost, throw away!) and spray with Safer's "Defender" garden fungicide. I then checked all my other rhodos and they too seem to be in the early stages of infection. The plant I first noticed is absolutely covered with the stuff and based on the advice I've received so far, I'll almost have to cut the whole thing down to get rid of all affected leaves. The others would take a very long time to spot prune effectively. WHAT SHOULD I DO?! Any advice would be greatly appreciated. Carmen

 

Probably mildew rather than rust. Look on the internet for information about that.