Orange rust on black raspberries and blackberries can be a disastrous disease that can mean removal of all diseased plants. It is characterized by bright orange spores that form on the undersides of the leaves.
The spores of orange rust do best in cool, wet weather. This disease has two periods of infection. In the spring, the bright orange spores (aeciospores) are produced on the leaves. These spores cause localized infections on the leaves. After this infection, teliospores form on the underside of the infected leaves. These teliospores produce basidiospores, which can cause systemic infections. Systemic infections affect the entire plant and are impossible to remove.
After the plant is infected with systemic infections, there is little that can be done. Prevention is key in keeping the plants disease free. Cultural controls are very important to disease control. Wild brambles should be removed from planting areas. Any infected plants should be removed as soon as possible. Controlling weeds and using good pruning techniques can improve air circulation and decrease the leaf wetness that is vital for leaf infection. Fungicides are also available to prevent plants from becoming infected.