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First Report of Elm Yellows in North Dakota. Robert W. Stack, Department of Plant Pathology, North Dakota State University, Fargo 58105. T. P. Freeman, Electron Microscope Laboratory, Department of Botany, North Dakota State University, Fargo 58105. Plant Dis. 72:912. Accepted for publication 19 July 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0912B.

In July 1986, an American elm (Ulmus americana L.) tree on a boulevard in Fargo, North Dakota, was showing progressive yellowing and die back of branches. Following the tests reported below, the tree was removed in late August, by which time about 50% of the crown was dead. Samples taken from the tree and cultured for vascular wilt fungi were negative. When fresh samples from small branches (3-5 cm) were examined, the inner bark showed a butterscotch-yellow discoloration and, when placed in a bottle for a short time, discharged a wintergreen odor, both symptoms diagnostic for elm yellows (2). Because elm yellows had not previously been known in this area, the diagnosis was confirmed by electron microscopy. When freshly collected phloem was fixed, thin-sectioned, and examined, amorphous cellular bodies typical of MLOs (1) were found within the sieve cells. This first report of elm yellows in North Dakota indicates a northward and westward extension of its reported range.

References: (1) E. J. Braun and W. A. Sinclair. Phytopathology 66:598, 1976. (2) W. A. Sinclair and T. H. Filer, Jr. Arborist News 39: 145, 1974.