Evaluation of Fungicidal Management of Alternaria Rot on Citrus Fruit in 2000-2001 Season

Abstract

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 in development, BAS 500, for disease management. A trial was conducted in a commercial Minneola tangelo grove with a history of Alternaria fruit rot. Within this grove, nine trees were sprayed monthly from August to December 2000 with BAS 500 at a rate of 0.25 lb active ingredient per acre. Another nine trees were not sprayed and served as controls. Disease severity was evaluated monthly from September 2000 to March 2001 by counting the number of infected fruit that had dropped from trees. No disease was evident on fruit from August through November, when fruit were green. By December the fruit had matured and turned color; additionally, the first fruit were detected with Alternaria fruit rot. In December and January there was little difference in the number of infected fruit on treated compared to nontreated trees. On the other hand, by February and March the cumulative number of infected fruit from trees treated with BAS 500 was 3.0 and 3.7 %, respectively, whereas the cumulative number of diseased fruit from nontreated trees during the same months was greater at 4.9 and 6.4 %, respectively. This study will be repeated next year with an adjusted spray schedule with the goal of increasing the level of disease control.