Rust is a common name for certain fungal infestations.  Rust infestations usually have a rusty reddish-brown color and leave a rust-colored dust on your fingers after handling the infected leaves.

During and after wet, cool spring weather, hollyhock rust infections are worse than usual.  Symptoms on the tops of leaves look like earwig damage, but when you look at the underside of the leaf, you will notice a big difference.  Small, brown bumps all along the leaf underside, with a corresponding pockmark on the leaf surface, are diagnostic characteristics of hollyhock rust.

Like other fungal problems, hollyhock rust is not curable.  Treatment with a fungicide is probably a waste of time, because once the rains stop and conditions are dry, the spores no longer infect the leaves.

At the end of the season, or if leaves drop during summer, remove them and send them to the landfill compost dump.

For more information about hollyhock rust, visit these sites:

http://www.coopext.colostate.edu...
http://www.ext.vt.edu/pubs/plantdiseasefs/450-613/450-613.html

Another common problem for hollyhocks in northern Utah is earwigs, a nocturnal insect that is about 3/4 inch long, shiny and flat, with pincher-type appendages on one end.  Earwigs crawl up onto hollyhock leaves at night, feed on leaf tissue, and hide under mulch or litter during the day.  Tiny holes all over the hollyhock leaves is a good indication of earwig infestations.  Earwigs are fairly difficult to control.  You can 'trap' them in a moistened, rolled-up newspaper, set out into the garden overnight.  In the morning, put the newspaper into a plastic garbage bag and throw it away.

Information compiled by Maggie Wolf,
Asst. Prof. Horticulture,
USU Extension Salt Lake County