Evaluation of Fungicidal Management of Alternaria Fruit Rot on Citrus in 2000 and 2001 Seasons

Alternaria 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.Arizona Citrus Research Counci