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Effectiveness of Metalaxyl and Fosetyl Al Against Phytophthora parasitica on Sweet Orange. L. W. Timmer, Professor, University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. W. S. Castle, Associate Professor, University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred 33850. Plant Dis. 69:741-743. Accepted for publication 5 March 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-741.

In a 3-yr study, metalaxyl and fosetyl Al were evaluated as soil drenches, trunk paints, and foliar sprays for control of Phytophthora parasitica in newly planted sweet orange trees on sweet orange rootstock. After application of metalaxyl as a soil drench or trunk paint, fungitoxic activity, as determined by bioassay, persisted for 34 mo in twigs and roots during the first 2 yr. In the third year, activity was less, probably because of dilution of the fungicide in the larger trees. Fungitoxic activity was less when metalaxyl was applied as a foliar spray. Application of fosetyl Al by all methods only occasionally produced fungitoxic activity detectable by bioassay. Both fungicides reduced foot rot incidence, but none of the treatments increased growth of the trees compared with untreated controls, indicating that root rot may have been of minor importance.