Only by nipping off affected leaves can you attempt to nip it in the bud, and no, there are no treatments other than chemical ones, and those don't work very well either once the infection is present. Now that you've had rust infected hollyhocks, the spores will be in the soil, so I recommend you don't try growing other hollyhocks next year. There are some varieties which are said to be rust resistant, but since you know you've got the spores, I'd leave it a while before trying them again. You should still get flowers on the plants you have, even with the infection.

Bayer makes a dithane preventative fungus fighter, but you'd have to use it every fortnight from leaf break to try to prevent the rust from taking hold.

Thankyou very much for the information Bamboo. I certainly won't be trying hollyhocks next year after the disappointment of this year.