Effect of Chloride Fertilizers on Development of Powdery Mildew of Winter Wheat. A. P. Grybauskas, Assistant Professor, Botany Department, University of Maryland, College Park 20742. A. L. Their, and D. J. Sammons. Former Graduate Research Assistant, and Associate Professor, Agronomy Department, University of Maryland, College Park 20742. Plant Dis. 72:605-608. Accepted for publication 4 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0605.

The role of spring-applied fertilizers containing the chloride (Cl) anion on the development of the powdery mildew (PM) disease of winter wheat was studied over three seasons. Additional factors included in the study were resistant and susceptible cultivars and conventional and intensive nitrogen fertilization. Plots were naturally infected with Erysiphe graminis f. sp. tritici. Single point-in-time disease assessments showed that Cl reduced powdery mildew severity but was significant only for the potassium (K) source. Area under the disease progress curve analysis of subsequent data showed a significant reduction of powdery mildew development due independently to K and Cl. The magnitude of the PM reduction varied with cultivar and leaf position within the canopy. Because of the lack of significant disease reduction with CaCl₂ and the high experimental rates used, reductions of PM due only to the Cl portion of some fertilizers may be too small to be of practical value. Yield increases were not directly associated with PM reductions.