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Characterization of Alternaria isolates associated with Alternaria Rot of CitrusAlternaria rot of citrus is a serious problem in citrus production world wide. In Arizona, the disease is most commonly found in Minneola tangelos and navel oranges grown in Maricopa County. Alternaria rot occurs primarily as a stem-end rot on fruit held in cold storage. However, under optimum conditions the disease occurs as a stylar-end rot in the orchards. In Arizona, the disease can significantly reduce yield, and annual fruit losses have been estimated at 0.5 box per tree. In terms of fruit quality, this disease can be a serious problem for the fresh fruit market as well as for the processing industry because only a small amount of rot imparts a bitter flavor and small black fragments of rotted tissue spoil the appearance of the juice. The application of fungicides is the most common tactic used to reduce losses to this disease. However, to date, no consistent reduction in disease has been achieved through chemical applications. This suggests that additional information relating to the biology of the pathogen and the epidemiology of disease will be necessary for the successful development of a reliable disease management program.
Evaluation of Fungicidal Management of Alternaria Fruit Rot on Citrus in 2000 and 2001 SeasonsAlternaria fruit rot on Minneola tangelos and navel oranges can reach economically important levels in central Arizona. The objective of this study was to test the efficacy of a new fungicide, Headline (BAS 500), for disease management. A trial was conducted in 2000 and 2001 in a commercial Minneola tangelo grove with a history of Alternaria fruit rot. In 2000, nine trees were sprayed monthly from August to December with Headline at a rate of 0.25 lb active ingredient per acre. Another nine trees were not sprayed and served as controls. In 2001, 15 trees were sprayed monthly from November, 2001 to February, 2002 with the same rate of fungicide used in 2000. Another 15 trees were not sprayed and served as controls. Disease severity was evaluated monthly from September to February in each season by counting the number of infected fruit that had dropped from trees. No disease was evident from September through November, when fruit were green. By December the fruit had matured and turned color; additionally, Alternaria fruit rot was first observed. Low numbers of infected fruit were recorded in December and January with higher numbers of infected fruit from non-treated compared to treated trees. In February the mean number of infected fruit from trees treated with Headline and non-treated trees was 2.1 and 3.8%, respectively, in the 2000 trial and 1.9 and 4.5%, respectively, in the 2001 trial. Disease was numerically reduced in both years; however, the difference was only statistically significant in 2001. The findings of this research suggest that Headline could provide meaningful reduction in the incidence and severity of Alternaria fruit rot in Minneola tangelo groves.