Septoria spot of citrus caused by Septoria citri is found in many citrus-producing countries around the world. It is a sporadic disease in California with most reports coming from Tulare Co. and Fresno Co. The pathogen is present on leaves and twigs in many orchards, and fruit infections probably occur commonly. Disease from these quiescent infections, however, only develops when plant tissues become senescent or environmental conditions predispose the host to infection.
First reported in the 1940s, recent outbreaks (2003-04 and 2004-05 seasons) have caused trade restrictions for California oranges in the Korean market. The risk of rejecting California citrus fruit in international markets required that: (1) rapid detection methods be developed for the pathogen for correctly diagnosing the disease; (2) conditions for fungal infection be studied; (3) management practices be revised, and (4) that a fruit incubation program be developed.