Rust - plant fungal disease

Signs  - Looks like the plant is going rusty (very descriptive these fungal diseases). Orange-brown pustules develop initially on the undersides of leaves. These may be unnoticed for some time, so by the time the pustules appear on the upper leaf surface and are noticed, the disease has taken hold. As with many fungal diseases that affect plant leaves, rust is not a particular disease but can be caused by any one of a whole group of different fungi. Different fungal species often have different host preferences and life cycles.

Damage  - Not usually a direct killer, but very unsightly and will affect growth, flowering and fruiting, badly affected plants can be so weakened they are unable to withstand winter frosts.

Treatment  - A fungal disease so one of the best ways of dealing with it is by good hygiene. Remove all dead leaves in autumn to prevent the spores from over wintering, burn the leaves or take them to the skip rather than use them for compost or you may well just perpetuate the problem.

Grow resistant varieties. Badly infected plants are best discarded - on the bonfire or tip - not the garden compost heap - and replaced.

Improve ventilation for plants grown under cover. Keep plants watered and fed well so they are able to fend off the effects of rust with their own immune system.

Hollyhocks will almost always get rust, you could deal with it by growing new plants each year, or as I do, by letting them self-seed, so selecting out the more resistant genes and then removing the worst affected leaves from the bottom of the stems and removing them from the garden. The leaves don't need to be removed until they are obviously on their way out.