Effects of Powdery Mildew, Triadimenol Seed Treatment, and Triadimefon Foliar Sprays on Yield of Winter Wheat in North Carolina

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Abstract
Wheat plots were established in central and eastern North Carolina in the falls of 1985 and 1986 to determine yield reduction caused by Erysiphe graminis f. sp. tritici on winter wheat [Triticum aestivum L.] cultivars Saluda and Coker 983. Check plots were compared with plots kept nearly disease-free with three to four foilar applications of triadimefon. The efficacy of triadimenol for mildew control when applied as a seed treatment, with or without different triadimefon foliar spray schedules, also was determined. Significant disease control resulted from foliar applications of triadimefon on both cultivars; however, the only consistent yield reductions were observed with Saluda. Triadimenol seed treatments lowered mildew severity and increased grain yields. Area under the powdery mildew curve was negatively correlated with yield; the correlation coefficient averaged -0.55 across four environments. No clear associations between disease and various yield components were detected. Regression models were constructed, and yield reductions of approximately 17% were observed in Saluda when disease severity reached 10% on the flag leaf by heading. Powdery mildew can limit yield in modern soft red winter wheat cultivars, although current levels of resistance in certain cultivars are sufficient to prevent large yield reductions.