Q: Why have some of my geraniums got rust like spots on the underside of the leaves ?
Rust is a fungal disease that if left untreated will kill the plant. Badly infected leaves will yellow and die. If the plant is badly infected it may be best to destroy it. Lightly infected plants can be treated with a fungicide labeled for the disease. Be sure to treat the undersides of the plant. Improving circulation with help prevent it in the future. Best And Happy Yardening, Nancy