Rust occasionally is found on cultivated geraniums. Distinct, reddish pustules form on the underleaf surfaces in a circular pattern. The upper surface is yellow in areas where pustules form. Control rust by removing infected leaves and spraying with a fungicide. Leaf spots begin as small, water-soaked spots on the underside of leaves.
Spots become well defined and slightly sunken in a few days.
Necrosis and wilting of the entire leaf follows, but the spots do not coalesce. Another symptom is rapid wilting of the leaf margin resulting in an angular pattern bound by the veins. Stem rot begins with one or two branches showing wilt. Eventually, the entire stem turns black with only a few leaves remaining at the terminals. Within the stem, the vascular fibers remain intact but the support tissue around the fibers is destroyed.