Rust fungus is easily identified by the many orange or red pustules on leaves or stems which break open and release masses of spores. Rust fungus grows within the leaf so there is usually a copy of the spores on the underside of the leaf as well. Different rust fungi attack different host plants so rust on gerananiums won’t spread to other types of plants. Rust is a common disease of calendulas, roses, snapdragons, geraniums, gerberas and beans. Rust can also attack turf. It has become a serious disease of frangipani, willows and poplar trees.
Orange pustules on leaves or stems.