Posted: 17/07/2015 at 08:52
Nice thought Rinus K, but no - rust is a fungal disease, spread by spores. It gets its name from the colour of the affected leaves.
I've frequently noticed that hollyhocks growing in beds seem almost guaranteed to contract rust, whereas I know of hollyhocks growing from gaps in paving, tarmac etc, with no soil at the surface seem to survive virtually rustless for years and years.
My conclusion is that the spores fall from the affected leaves and if they fall on the soil they linger there over the winter to reinfect the plant the following year, whereas if they fall on paving, tarmac etc the spores are washed away in the winter, hence less chance of re-infection. Just a thought