The rust fungi are described as biotrophs; that is, they grow within the living tissues of the plant and extract nutrients from the cells. Although they do not kill tissues rapidly, heavy attacks by rusts can cause leaves to fall prematurely, which is the case with raspberry rust.
It is the spores produced in the orange pustules on the underside of the leaves that are mainly responsible for spreading the disease from leaf to leaf and plant to plant during the summer. Those produced in the black pustules in late summer are overwintering spores which, as well as surviving on the fallen leaves, can also become attached to the stems and to posts, wires, etc.
Infection is favoured by wet or humid conditions. The disease is therefore most problematic during wet summers and where air circulation through the canes is poor.
Unlike some other rust fungi the life cycle for raspberry rust does not involve an alternate host.