This disease of hollyhock is caused by the microorganism Puccinia malvacearum. This fungus belongs to a large and special group of fungi which may attack a wide range of blooming garden plants in the landscape. There are many rust diseases which may attack ornamentals, grasses and vegetables. Many of the fungi classified as rusts may have a complex life cycle which requires two similar hosts to complete; that is the fungus may spend part of its life on separate plants. The hollyhock rust fungus may also affect mallow (Malva sp), a common weed. The mallow weed can serve as a reservoir for the fungus and be responsible for new infections on hollyhock. The fungus produces microscopic spores that are responsible for spread of the disease. These spores can be dispersed by the fungus and carried on wind currents for several miles from the source. Damp and humid conditions in the spring contribute to disease onset and severity.
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