Ash Yellows, Drought, and Decline in Radial Growth of White Ash. Ying Han, Former Graduate Research Assistant, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse 13210-2788. John D. Castello, and Donald J. Leopold. Associate Professor, and Associate Professor, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse 13210-2788. Plant Dis. 75:18-23. Accepted for publication 28 August 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0018.

The effect of MLO infection and drought on the radial growth of white ash trees was measured using standard dendrochronological techniques. Both MLO infection and drought stress caused reductions in the radial growth of white ash, but not all MLO-infected trees declined in radial growth. The effect of regional drought on the radial growth of white ash was investigated on 15 of 41 permanent research plots by comparing summary tree ring indices of the white ash within these plots with mean Palmer Drought Severity Indices for April through September. Growth decline associated with drought stress was reversible when drought stress abated. Growth decline associated with drought stress and MLO infection was more severe than that associated with MLO infection alone and did not appear to be reversible. Both ash yellows and growth decline were related to stand age, becoming less prevalent in older stands.