Alternaria is spread by airborne spores. Rain events or sudden changes in relative humidity also favor spore release. Spores are produced on older lesions formed on wilted twigs and mature leaves. Some spores come from fruit lesions but they are not a major inoculum source. Even the leaf contributes to the inoculum. Although the spores are airborne and carried by winds, alternaria brown spot is often spread among groves on nursery stock transported by humans.
Other Common Names
Alternaria brown spot (ABS), alternaria brown spot of mandarins, brown spot
Serrano, D., Serrano, E., Dewdney, M., and Southwick, C. (2010). Citrus Diseases. USDA/APHIS/PPQ Center for Plant Health Science and Technology. [09-14]