Effectiveness of Fosetyl-Al Against Phytophthora parasitica on Tomato. R. M. Davis, Extension Plant Pathologist, Department of Plant Pathology, University of California, Davis 95616. . Plant Dis. 73:215-217. Accepted for publication 31 October 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0215.

Multiple prophylactic foliar sprays of fosetyl-Al (12 g a.i./L, optimum concentration) were more effective than a single application in reducing root rot of potted tomato plants inoculated with Phytophthora parasitica. Fosetyl-Al provided little or no control of root rot when applied to the plants after inoculation with a suspension of zoospores. Efficacy of fosetyl-Al decreased as the interval between treatment and inoculation increased; little control was obtained when 3–4 wk passed between final application and inoculation with P. parasitica. The evidence indicated that the concentration of the fungicide in the plant needed to be maintained over a long period of time with multiple applications to control the disease.