Well this is on of my ‘learn as you go’ type of posts. I’ve had gorgeous hollyhocks for a few years now (grown from seed originally!). They really are a showstopper by sheer size alone! Last year I noticed that the leaves started to become mottled just about at the same time that the flowers started appearing. I thought maybe it was just the lifecycle of the plant – obtaining its’ fruition and then dropping leaves as it slowly ends its cycle for the season. However, this year that started happening much earlier and it was much more invasive. I discovered the culprit is a rust fungus (Puccinia heterospora). It is very disfiguring and even though it does not destroy the plant, you’d almost rather it be gone that look at it. I am currently treating my plants with a fungicide. Not sure how I’ll do, but will update this post as I go along. Meanwhile, I have copied off some information from a site “Gardening Know How” below.
Caused by the fungus Puccinia heterospora, hollyhock rust is a disfiguring disease that infects members of the Alcea (hollyhock) family. It begins as yellow spots on top of the leaves with rusty pustules on the undersides.
Over time the spots can grow together and destroy large sections of the leaves, causing them to die and drop off. At this point, the stems may also develop spots. Although the plant may not die, you may want to put hollyhocks with rust fungus out of their misery because of the severe disfigurement.
Does hollyhock rust spread to other plants? Yes, it does! It only spreads to other members of the Alcea family, so most of your other garden plants are safe. There are mallow weeds that are members of the family that can act as a host reservoir for the disease, so it’s best to keep weeds away from hollyhocks.
Hollyhock rust disease occurs anywhere you find hot, humid temperatures. This is especially true in the southeast where these conditions persist throughout most of the summer. Below are some hollyhock rust treatments to try. Bear in mind that you’ll have more success if you employ several of these strategies at once.
When you first notice rust spots, pick off the leaves and either burn them or seal them in a plastic bag and discard them.