VIEW ARTICLE

Disease Control and Pest management

Effect of Triadimenol Seed Treatment and Timing of Foliar Fungicide Applications on Onset and Extent of Powdery Mildew and Leaf Rust Epidemics. K. L. Everts, USDA, ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616, Present address: Seed Research, Busch Agricultural Research, Inc., Ft. Collins, CO 80524; S. Leath, USDA, ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 83:557-562. Accepted for publication 22 January 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-557.

Powdery mildew and leaf rust occur yearly in wheat-growing areas of the southeastern United States. However, the time of onset and peak severity differ between diseases, and consequently, wheat plants are subject to disease stress throughout a long period of the growing season. Three cultivars of winter wheat varying in their level of disease resistance and either seed treated with triadimenol or untreated were planted at Kinston and Plymouth, NC, during the fall of 1989 and 1990. Plots received foliar fungicide applications at different times during the two growing seasons to determine how cultivar, seed treatment, and time of foliar fungicide application affected development and severity of powdery mildew and leaf rust, yield components, and yield. The extent of mildew and leaf rust and their impact on yield components and yield varied between environments. At Kinston, where both powdery mildew and leaf rust were severe during 1989–1990 and 1990–1991, mildew positively influenced tiller number, and rust influenced 500-kernel weight and number of seeds per head. Powdery mildew was present only at low levels at Plymouth; leaf rust reduced 500-kernel weight and yield. Seed treatment reduced the extent of powdery mildew in all environments and reduced leaf rust at Kinston during 1989–1990 and at Plymouth during 1990–1991. When seed was treated with triadimenol, the optimum time of foliar fungicide application for maximum yield response was delayed in six of nine cultivar × environment combinations.