Two rust species, M. larici-epitea and  M. capraearum,  are common in willow plantations, with M. larici-epitea being most predominant. Melampsora larici-epitea infects only leaves while M. capraearum infects both leaves and young stems. The two rust species have a complex life-cycle (below), overwinter on fallen willow leaves and have an alternate host, European larch (Larix decidua).  

During late spring – autumn, the rusts are seen as yellow/orange pustules containing urediniospores. The uredinospores are capable of producing the next generation of the same type of spores in 6-7 days. These urediniospores are responsible for many cycles of disease in a growing season resulting in damage on willow. In the autumn, the rusts produce teliospores and overwinter on fallen willow leaves. In spring, the teliospores germinate to produce basidiospores that infect larch. Genetic materials are reshuffled when teliospores germinate and genetic exchange takes place when spermatia fertilise receptive hyphae. Fertilization of receptive hyphae by spermatia triggers formation of aeciospores which infect only willow, not larch.