The bottom of my black raspberry leaves are covered with an orange substance. What is it?
The orange substance on your black raspberry leaves is orange rust. Orange rust occurs on black and purple raspberries and most varieties of blackberries. Orange rust does not occur on red raspberries.
Orange rust produces masses of bright orange spores on the undersides of leaves in spring. Canes or shoots bearing the rust-infected leaves are often weak and spindly. The disease eventually kills the entire plant, including the roots.
Infected plants cannot be cured. To control, dig up and destroy all plants with rust-infected leaves. Start new plantings from rust-free nursery stock. Orange rust can also originate from wild brambles. Destroy any wild brambles in the area.