Orange rust, caused by the fungus Arthuriomyces peckianus, a serious, systemic rust that infects all plant parts of black raspberries and blackberries. Symptoms are most apparent in spring when the undersides of leaves turn orange.
Primocanes emerging in spring may appear stunted and are strap-like.
More information:
- Orange Berry Rust
- Orange Rust of Brambles – (Ohio State)
Use these resources if you need additional help with diagnosis and to find solutions to your problem.