Species of Ramularia and Phyllosticta cause leaf spots on many plants. Ramularia infections are sometimes called white moulds because of the white fungal outgrowth from infected tissues. Infections caused by rust fungi in Puccinia are not strictly classified as leaf spots, but the symptoms caused by P. primulae on primulas will be seen by gardeners as spots.
Ramularia and Phyllosticta produce spores in the infected tissue and these spread by water to form new infections. They can also survive over winter in dead tissues in the form of resting structures. Since most primulas are perennial, there is probably some survival of the pathogens in lesions on leaf rosettes from one year to the next.
Puccinia primulae spreads by means of airborne spores produced from the small orange structures on the undersides of infected leaves. It also has a type of resting spore which carries the fungus through the winter, although it can also survive as infections on the leaves of perennial rosettes. The whole life cycle is completed on primulas, there is no alternate host. Puccinia primulae seems to be confined to Primula vulgaris (primrose) and P. veris (cowslip).