Ash Crown Condition and the Incidence of Ash Yellows and Other Insects and Diseases in Illinois, Iowa, Missouri, and Wisconsin. Christopher J. Luley, Forest Pathologist, Missouri Department of Conservation, Jefferson City 65102. Manfred E. Mielke, John D. Castello, Jane Cummings Carlson, James Appleby, and Roy Hatcher. Plant Pathologist, USDA Forest Service, St. Paul, MN 55108; Professor, State University of New York, College of Environmental Science and Forestry, Syracuse 13210; Forest Pathologist, Wisconsin Department of Natural Resources, Madison 53711; Entomologist, Illinois Natural History Survey, Champaign 61820; and Forester, Iowa Department of Natural Resources, Ames 50010. Plant Dis. 76:1209-1212. Accepted for publication 31 July 1992. 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, 1992. DOI: 10.1094/PD-76-1209.

Seventy-nine plots in Illinois, Iowa, Missouri, and Wisconsin were surveyed in 1990 for ash yellows (Ash Y) and other diseases and insects. Twenty-one of 38 white ash and 20 of 41 green ash plots had trees with Ash Y based on the 4’,6-diamidino-2-phenylindole (DAPI) DNA-staining technique or the presence of witches’-brooms. Ash Y was widely distributed in all states except Wisconsin, where trees in only two of 20 plots were affected. Other than witches’-brooms, symptoms previously associated with Ash Y were present on trees in plots that tested both positive and negative for mycoplasmalike organisms. Approximately 50% of the ash trees had greater than 10% crown dieback, and 5% of the trees were dead. Overall, trees representing about 12% (6–7 m³·ha^–1) of the total ash volume had 50% or greater crown dieback. There was no significant difference in mean crown condition rating of the ash trees in Ash Y-positive and Ash Y-negative plots. Other disease and insect problems were common but were not considered to be major causes of crown dieback. The primary cause of crown dieback of ash in the Midwest is unknown.