Effect of Triadimenol Seed Treatment and Triadimefon Foliar Treatment on Powdery Mildew Epidemics and Grain Yield of Winter Wheat Cultivars. P. E. Lipps, Associate Professor, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. L. V. Madden, Associate Professor, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 72:887-892. Accepted for publication 28 June 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0887.

The effect of triadimenol seed treatment and triadimefon foliar treatment on powdery mildew epidemics and grain yield was studied over a 3-year period on winter wheat cultivars with different susceptibilities. Area under the disease progress curve (AUDPC) was calculated from disease assessments taken from first node visible growth stage (Feekes growth stage 6) to completion of flowering or kernels watery ripe (growth stage 10.5.4 or 11.1). Analysis of variance of AUDPC indicated that the main effects of seed treatment, foliar treatment, and cultivar were significant all 3 years of the study. However, the main effects of seed treatment, foliar treatment, and cultivar on yield were significant in only 2, 1, and 3 years, respectively. The only significant interaction was cultivar by triadimefon foliar treatment. This indicated a differential response of cultivar to foliar treatment for yield in all 3 years. Foliar treatment reduced AUDPC for all cultivars, although the greater reductions were for the more susceptible cultivars. Triadimenol seed treatment resulted in lower AUDPC compared with carboxin-thiram treatment. The most susceptible cultivars were Becker and Hart; the least susceptible were Tyler and Scotty, with Adena, Cardinal, and Caldwell being intermediate. A single triadimefon foliar treatment applied at ligule of flag leaf just visible to boot stage (growth stage 9 to 10) provided substantially greater disease control and larger yield increases than triadimenol seed treatment.

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