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Preventative and Curative Control of Downy Mildew of St. Augustinegrass by Metalaxyl. B. D. Bruton, Research Plant Pathologist, Agriculture Research Service, U.S. Department of Agriculture, P.O. Box 267, Weslaco, TX 78596. R. W. Toler, Professor, and M. P. Grisham, Assistant Professor, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843. Plant Dis. 70:413-415. Accepted for publication 12 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-413.

Metalaxyl applied at 14.2, 28.4, 56.7, and 85.1 g a.i./93 m2 as foliar sprays provided both protective and systemic activity against Sclerophthora macrospora on St. Augustinegrass. All rates of metalaxyl reduced the percentage of diseased leaf blades from greater than 90% on the day of application to 0% 28 days later. Histological examination of S. macrospora-infected leaf blades 7 days after application of metalaxyl showed that the fungicide can eradicate the fungus. Both spring and fall/spring applications of metalaxyl in the field controlled downy mildew. Fenaminosulf demonstrated little or no control of St. Augustinegrass downy mildew.

Keyword(s): histopathology, Stenotaphrum secundatum, turfgrass.