Development of Control Measures for Alternaria Fruit Rot on Roanges in Arizona

Abstract

The incidence and severity of Alternaria fruit rot on navel oranges has increased in Maricopa County. The objectives of this study were to test the efficacy of two fungicides, Kocide 101 and Rovral, for disease control and to determine an application schedule that will result in optimum control of disease. In 1994, compared to nontreated trees, a significant reduction in the number of dropped oranges occurred on trees sprayed one to five times with Rovral at monthly intervals from April through August. In the same year, monthly applications of Kocide 101 from April through August were no better than leaving trees untreated. In 1995, Rovral treatments from March through August provided no apparent beneficial effects on control of Alternaria fruit rot, while a single application of Kocide 101 in December, January, or February resulted in significantly less dropped oranges compared to nontreated frees. Because of the inconsistent activity of Kocide 101 and Rovral in these two studies, an additional trial is in progress during 1996. The additional data from 1996 may help identify when and what fungicide(s) could provide significant control ofAlternaria fruit rot of navel oranges in Arizona.