Q: I have some high mallow on which some of the leaves are turning a yellowish color with little spots on them. Can you tell me what it is?

A: High mallow, Malva sylvestris, is also known as French hollyhock. As such, it is susceptible to the same problems that affect ornamental hollyhock.

In your case, the problem is hollyhock rust, Puccinia malvacearum. The bumps (pustules) are characteristic of most rust diseases.

The fungus overwinters on the bottom leaves and old stems. Cut back the plants immediately after flowering. Clean up old leaves and remove infected leaves as they are noticed.

For maximum protection begin fungicide treatments in early spring when the first leaves are expanding. Fungicides containing chlorothalonil (Daconil), neem oil, or myclobutanil (Immunox) are effective.

Read more here.