Effect of Fungicide Application Timing on Control of Powdery Mildew and Grain Yield of Winter Wheat. P. E. Lipps, Associate Professors, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. L. V. Madden, Associate Professors, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 73:991-994. Accepted for publication 26 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0991.

Wheat cultivars Becker and Caldwell in 1987 and Becker and AGRA GR855 in 1988 were treated with a single foliar application of triadimefon fungicide at six different growth stages (GS), from GS 6 (first node visible) to GS 10.5.4 (end of flowering). Generally, applications at GS 6 and GS 8 prevented further development of powdery mildew, except on Becker in 1988, when an increase in disease severity was detected 18 days after treatment at GS 6. Plots treated as late as GS 9–10 in 1987 and GS 10.3 in 1988 had significantly (P = 0.05) lower values for area under the disease progress curve (AUDPC) than untreated plots. Yield of fungicide-treated plots was significantly greater than that of the untreated control when fungicide was applied at or before GS 10.3 for Becker and Caldwell in 1987, at GS 6 for Becker in 1988, and at GS 6 and GS 9–10 for AGRA GR855 in 1988. Results indicate that early (at GS 6–8) applications of fungicide provide greater powdery mildew control and higher yield than applications later in the season.

Keyword(s): chemical control, Erysiphe graminis f. sp. tritici, Triticum aestivum, yield loss.