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Ash Yellows in the Northern Great Plains Region. J. A Walla, Plant Pathology Department,; North Dakota State University, Fargo 58105 . Y. H. Guo, Plant Sciences Department, North Dakota State University, Fargo 58105. Plant Dis. 80:343. Accepted for publication 17 January 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0343D.

Ash yellows was first reported in the Great Plains in southeast North Dakota (ND) in 1993 (2). We report here that ash yellows occurs in green ash (Fraxinus pennsylvanica Marsh.) in other areas of ND and in Montana (MT), Nebraska (NE), and South Dakota (SD). The sampled trees were found during incidental travel, not by organized survey. They included planted and wild trees, each in rural and urban settings. Those in ND, SD, and NE and one MT site were sampled because they had witches'-brooms. Those at the other MT site were sampled because the adjacent trees had severe dieback; the three sampled trees at this site consisted of stumps with sprouts. Observations, tissue collections from most trees, and assays were made between August 1993 and August 1995 by the authors. Tissues from one of the observed trees in MT were collected by J. Scianna, Bridger Plant Materials Center. A total of 15 trees from 12 sites were sampled. Samples from 11 trees at 10 sites consisted only of succulent tissue (shoots, petioles, leaf veins) from witches'-brooms (10 were positive for ash yellows). Samples from four trees at three sites consisted of roots instead of (three trees at two sites, two were positive) or in addition to (one tree, positive) tissues from witches"-brooms. The cross-sectioned plant tissues were examined with immuno-fluorescence microscopy using an ash yellows-specific monoclonal antibody (1). Infected and noninfected periwinkles were used as positive and negative controls, respectively. Asymptomatic green ash seedlings were used as additional negative controls. Ash yellows was confirmed in Bur leigh and Emmons counties in south central ND and Billings County in southwest ND; Brookings County in northeast SD and Minnehaha County in southeast SD; Burt County in northeast NE, Butler County in southeast NE, and Garfield County in central NE; and Carbon County in south central MT. Ash yellows was confirmed in one tree in each of these counties except for Carbon County, MT, where four infected trees at two sites were identified. Ash yellows was not confirmed on one additional tree with a witches'-broom at the Brookings County, SD, site or on single trees with witches'-brooms at one site each in Saunders County and Dodge County, NE. The condition of the two infected trees in south central ND appeared to be good, whereas that of all other infected trees was poor, as judged by apparent vigor and extent of crown dieback. This report documents substantial extension of the known range of ash yellows to the northwest, extending it to the western side of the native range of green ash.

References: (1) Y. H. Guo and T. A. Chen. Phytopathology 83:243, 1993. (2) J. A. Walla et al. Plant Dis 78:432, 1994.