Hollyhocks are tall stalk plants with large flowers that are bright in color. The plant will bloom for two months during the midsummer months. The plants are easy to grow; however, they are susceptible to a fungus disease called rust. Rust can be controlled when proper measures are taken.
Hollyhock is an easy-to-care-for plant that prefers full sun and organic soil. It is considered a short-lived perennial or herbaceous biennial and will reseed itself under proper conditions. Hollyhock seed can be collected at the end of the season and manually reseeded in spring. The plants grow up to 8 feet in height and grow well near fences, next to buildings and for back borders. Hollyhocks will grow well in the growing zones 2 through 9.
Few diseases affect hollyhocks; however, hollyhock rust is a problem. Rust is a common and serious disease that is found in most hollyhock gardens and is spread by the weed mallow, which is a disease reservoir. The rust disease is a fungus that spreads by rain droplets splashing on leaves and through air transfer. If not treated, the disease intensifies through summer and will eventually kill the plant. Rust will overwinter and infect the crowns of sprouting plants in spring.
The rust disease in hollyhocks appears as rust-colored bumps on the underside of the leaves and steams of the plant. The disease starts as small rust flecks and grows into raised bumps or pustules that will spread to all parts of the plant greens. An infected plant will appear limp and ragged.
Control of Disease
There is no cure for a rust infection. At the first signs of rust, remove infected leaves and destroy them. Watch the plants through the growing season and remove any signs of the disease before it spreads. Since the fungus will overwinter, fall cleanup of plant debris is crucial for controlling the spread. Cut back and destroy all plant stems and collect all loose leaves from the plants. Also remove all mallow weed from the area. Do not compost infected plants. When new sprouts appear in spring, remove the first two leaves as an attempt to remove any spores remaining from the previous season.
Apply a fungicide to new plant growth in spring for prevention. The rust disease will attack plants that are weak or under stress, so always keep plants watered. Do not overwater, as this will promote fungus growth. Remove weeds and provide air circulation around the plants to promote leaf drying in the plants.