Orange rust

Orange rust is a disease of black berry and black raspberry. Purple raspberry may also become infected, but red raspberry is resistant. This rust occurs in two different forms with very similar symptoms. One form has a long cycle and affects mainly black raspberry (Arthuriomyces peckianus), and the other has a short cycle and affects mainly blackberry (Gymnoconia nitens).

Orange rust is one of the more serious diseases of susceptible brambles. It should not be confused with the late leaf rust disease of red raspberries.

Symptoms
Lower leaf surfaces become covered with blister-like masses of yellow-orange spores by late May or early June. These spores serve to spread the disease to other plants. In addition, heavily infected leaves may die, and infected shoots will be weak, spindly and have very few, if any thorns.

Treatment
As the rust becomes systemic in the host, remove and destroy infected plants as soon as they appear in the spring. Thin healthy canes and keep weeds down to promote good air circulation which helps prevent spore germination and infection. There are no effective fungicides for control of orange rust at this time.

Prevention
To control orange rust begin by planting only healthy black raspberry and blackberry stock. Eradicate infected wild blackberries and black raspberries near your raspberry patch.