Description: Hollyhock rust is a fungal disease that is most prevalent on hollyhocks, but other members of the mallow family are also susceptible. The fungus is introduced by infected plants. Fungal spores can travel by wind and splashing water as well. Warm, humid weather supports the fungal growth. The fungus can overwinter on infected plant debris and spread to new plants in the spring.
Symptoms: Orange-yellow spots develop on the lower leaves and sometimes brown spots will appear on stems. Raised bumps that are reddish-brown later develop on the undersides of leaves beneath the orange-yellow spots. These are the reproductive structures of the fungus. The infected leaves may develop holes and eventually die back.
Control: Prevention is the best approach against hollyhock rust. Begin with healthy
plants each year and remove all plant debris from the previous growing season. Allow
adequate spacing between plants so the fungus is less likely to spread if one plant is
infected. Water at the soil level and avoid splashing on the plant.
If a plant develops rust, remove the infected leaves immediately and dispose of them. Plants that have a history of infection may benefit from a preventative fungicide when the weather is warm and humid. Spray every two weeks until the weather is dry. Sulfur and myclobutanil (Immunox, Monterey Fungi-Max, F-Stop Lawn & Garden Fungicide) are recommended. If the temperature rises above 85 degrees F within 24 hours of application the sulfur treatment may cause damage to treated leaves.
