Symptoms and Signs
Newly emerging leaves are usually stunted, deformed, and yellowish. From afar, the plant tends to have a lightly foliated, spindly appearance. Later, the undersides of diseased leaves exhibit irregularly shaped, waxy orange aecia that soon turn to a powdery bright orange as they rupture and release spores. Late in the season brown-black pustules of the teliospore stage will develop on lower leaf surfaces. A notable symptom is the growth many small, typically weak shoots from the base of the plant; such shoots are not usually productive.
Comments on the Disease
Orange rust fungi are distinguished from each other by differences in spore appearance and by whether they have a long (Arthuriomyces) or short (Gymnoconia) life cycle. This disease can be found on blackberries and on black raspberries. Orange rust is systemic and, therefore, grows into plant crowns and roots and remains in the plant for life. Although this pathogen is not known to kill plants outright, it weakens them severely, and systemically infected plants produce few or no blossoms.
Once confirmed to be infected with orange rust, promptly uproot and remove diseased plants from the field and destroy them. Do this roguing before the production and release of spores. Although this control measure may seem severe, it must be done in order to prevent the further spread of orange rust. The best control measure is prevention and starting out with clean plant stock by obtaining disease-free stock from a reputable nursery.