Hollyhock Rust GD 26
Ann Hazelrigg, Plant Diagnostic Clinic Coordinator
Rust is the most common disease affecting the hollyhock. All green parts of the plant are susceptible to infection. Death
rarely occurs though severe infection causes yellowing and premature defoliation of the leaves. If early signs of the
characteristic rust-colored pustules go unnoticed, the plant will soon be entirely infected; unless properly controlled,
the fungal disease will survive year to year.
Rust infections first appear as yellow to brownish pustules about the size of pinheads on the underside of lower leaves
on the hollyhock stalk. Shortly after pustule development larger yellow to orange spots with reddish centers develop
on the upper surface of the leaves. Severe infection promotes the spread of pustules to the upper surface of the leaves
as well as the stem and the green flower parts of the plant. Rust infection will spread very fast from leaf to leaf, killing
more mature leaves and making the plant unsightly.
Hollyhock rust is caused by the fungus Puccinia malvacearum. The fungus survives the winter on leaves and stems
that were infected during the growing season. The fungus can also survive on the plants of the common, round-leaf
mallow weed Malva rotundifolia throughout the winter. In the spring spores produced by the fungus are spread by
air currents to young hollyhock plants. In this way, new plants are infected year to year. The rust will quickly transfer
from leaf to leaf and plant to plant.
Infected leaves should be removed and burned as soon as they are noticed. Rust-infected stalks should be removed as
soon as the plants are through blooming and destroyed with any leaves that have fallen. The round leaf mallow weed in
the vicinity should be destroyed as well to insure that the fungus has no material on which to survive the winter. Dusting
the plants with sulfur or spraying with fungicides will aid in controlling the disease. Many of the all-purpose garden
sprays or dusts contain chemicals that will aid in the disease control. Dusting and spraying should begin early in the
season making sure to keep new foliage covered with the spray or dust, especially the underside of the foliage.
Providing good air circulation about the plants will lessen the chance of the disease spreading. This may necessitate
thinning out some plants.
Before using any pesticide, read the label and follow all precautions!
Based on material developed in 1992.