Leaves with orange powder on them indicate rust infection. Two types of rust occurs on raspberry and blackberry leaves: Late Leaf Rust, and Orange Rust. Distinguishing between the two is important as management strategies for the two rust diseases differ greatly.
Late Leaf Rust, is caused by the fungus Pucciniastrum americanum. It occurs on the undersides of leaves.
The upper leaf surface may develop yellow blotches, curl upwards and turn brown when infected. This disease occurs during periods of cool, damp weather, especially in autumn.
Fruit infections may also occur with late leaf rust and appear as small orange-yellow patches on the fruit surface.
More late leaf rust information
Orange rust, caused by the fungus Arthuriomyces peckianus, is a much more 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.
