Hollyhock rust is caused by the fungus Puccinia malvacearum. The undersides of infected leaves show raised brown spots about the size of a pinhead. The upper leaf surfaces usually show a yellow to orange discoloration above the brown spots. Infected areas may run together and destroy large portions of the leaf. Stems may also be infected.
To control rust on hollyhock, remove the first leaves on which rust is evident. Spraying with a fungicide, such as Daconil 2787, can be effective. Sprays should start when the new growth appears in the spring and repeated 7 to 10 days apart. When the flowering season is over, cut the plants back to the base and destroy the infected plant parts.
This article originally appeared in the June 16, 1995 issue, p. 89.