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Ash Yellows: Geographic Range and Association with Decline of White Ash. W. A. Sinclair, Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908. R. J. Iuli, A. T. Dyer, P. T. Marshall, J. A. Matteoni, C. R. Hibben, G. R. Stanosz, and B. S. Burns. Department of Plant Pathology, Cornell University, Ithaca, NY 14853-5908; Indiana Department of Natural Resources, Vallonia 47281; Agriculture Canada Research Station, Vineland Station, Ontario L0R 2E0, Canada; Brooklyn Botanic Garden Research Center, Ossining, NY 10562; Pennsylvania Department of Environmental Resources, Middletown 17057; and Vermont Agency of Environmental Conservation, North Springfield 05150. Plant Dis. 74:604-607. Accepted for publication 12 January 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0604.

Ash yellows, a disease of Fraxinus spp. putatively caused by mycoplasmalike organisms (MLOs), was found to occur from Iowa and Missouri eastward to the Ottawa Valley of Canada and the Atlantic Coast in southern New England, as well as in scattered localities outside this range. New distribution areas recorded include Connecticut, Kentucky, Michigan, Missouri, Ohio, Pennsylvania, Utah, and the province of Quebec. In Utah, velvet ash (F. velutina) was affected, a new host record. The association of MLOs with decline in white ash (F. americana) was studied on 88 sites in four states (Indiana, New York, Pennsylvania, and Vermont) and southern Ontario. MLOs were detected by fluorescence microscopy in ash at 35 of 51 sites where severe dieback was common but at only five of 37 sites where dieback was scarce or absent. On sites where MLOs occurred, they could not be detected in all declining trees. Dieback at sites without MLOs was often associated with adverse soil conditions or evidence of prior injury. Thin canopies and slow growth of white ash were common on sites with and without MLOs.