Alternaria and Colletotrichum diseases in Citrus: Epidemiology and control in San Joaquin Valley CA

In the last two to three years, growers have brought to our attention samples of oranges and mainly mandarins infected with Alternaria and Colletotrichum species. Significant damage was reported by some growers and confirmed during our visits to orchards of Fresno and Tulare counties where an excessive number of fruit and leaf drop was observed. We intend to access the extent of this problem in the San Joaquin Valley, determine the main infection period(s), propose an effective control program, and address the risk of fungicide resistance. The expected output will be the recommendation of fungicide programs to reduce the incidence of these pathogens, resulting in lessened crop losses.