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Comparison of the Effects of Sublethal Doses of Triadimefon to Those of Rate-Reducing Resistance to Erysiphe graminis in Wheat. R. D. Schein, Professor of plant pathology, Department of Plant Pathology, Pennsylvania State University, University Park 16802; R. R. Nelson(2), G. G. Thomas(3), M. H. Royer(4), and O. Borges(5). (2)(3)(4)(5)Evan Pugh Professor, graduate assistant, postdoctoral assistant, and visiting scientist, respectively, Department of Plant Pathology, Pennsylvania State University, University Park 16802, (5)Present address: Facultad de Agronomia, Universidad Central de Venezuela, Maracay. Phytopathology 74:452-456. Accepted for publication 9 November 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-452.

Attempts to control plant disease by the use of rate-reducing resistance were stimulated by the periodic demise of race-specific resistance genes selected to give almost complete control. Similarly, some systemic fungicides, used at rates determined to give almost complete control, result in the selection of fungicide-tolerant populations. Reasoning that these fungicides at sublethal dosages may affect the same components of disease development as rate-reducing resistance, we postulated that fungicides used in this way might enable management of some plant diseases at less cost and with reduced risk of causing rapid selection of fungicide tolerant populations. By testing triadimefon against powdery mildew of wheat, it was determined that disease efficiency and sporulation capacity were reduced greatly by amounts less than one-one hundredth of the recommended dosages. We conclude that studies of disease management with such small dosages are in order to see if such procedures will lessen the rate of development of fungicide tolerance and increase the commercial life of both cultivars and fungicides.