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.