Raspberry rust

Raspberry rust (sometimes called raspberry yellow rust) is a disease of the foliage of raspberries, caused by the fungus Phragmidium rubi-idaei. The fungus produces a number of different types of spore depending on the time of year and, as these different spores are produced, so the appearance of the disease changes. The microscopic spores are produced in structures called pustules. Leaf wetness is needed for infection, so attacks are worst during prolonged wet weather.

Symptoms
In spring and early summer: clusters of slightly raised, yellow pustules appear on the upper leaf surface, usually beginning on the bottom leaves
As summer progresses: the pustules described above become less conspicuous, but numerous tiny orange pustules begin to be produced on the lower leaf surface, often with small yellow spots on the corresponding upper surface
Large numbers (scores, or even hundreds) of these ‘summer spore’ pustules may be present on a single leaf
Severe infection may lead to premature shedding of leaves
In late summer and autumn: the orange pustules are gradually replaced by black ones, containing overwintering spores