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<br />How to Identify and Manage Dutch Elm Disease <br /> <br />Page 6 ofl6 <br /> <br />Symptoms often observed in Symptoms visible Symptoms appear in summer and <br />early summer, but may be from July to early fall. <br />exhibited any time of the September. <br />growing season. <br />Brown streaking in sapwood. No discoloration in No discoloration in sapwood. <br /> sapwood. <br />No discoloration in inner Tan discoloration of No discoloration of inner bark. <br />bark. inner bark. <br />No wintergreen odor. Wintergreen odor in No wintergreen odor. <br /> inner bark. <br /> <br />Elm yellows. This disease, which is also called elm phloem necrosis, is caused by a <br />phytoplasma (microscopic bacteria-like organism) which systemically infects the phloem <br />tissue (inner bark) of the tree. It is a serious disease that causes tree death. Symptoms of elm <br />yellows differ from OED in that the leaves turn yellow (not brown and wilted) and drop <br />prematurely, and the symptoms appear in the entire crown at the same time. The brown <br />streaking which OED causes in the sapwood is absent, but the inner bark develops a tan <br />discoloration and a characteristic wintergreen odor. <br /> <br />Bacterial leaf scorch. This disease is caused by the bacterium Xylella fastidiosa, which <br />infects and clogs the water conducting tissues of the tree. Infection by this bacterium causes <br />a slow decline over many years. Once a tree is infected, symptoms recur annually. <br />Symptoms of scorch are irregular browning along the leaf margin with a yellow border <br />between green and scorched leaf tissue. Older leaves on a branch are affected first. <br /> <br />Disease Cycle of Dutch Elm Disease <br /> <br />The biology, or "disease cycle," of OED depends upon the host, the fungus and the means <br />by which the fungus moves into new host trees (figure 4). <br /> <br /> <br />http://www.na.fs.fed.uslspfo/pubs/howtos/ht_dedlht_ded.htm <br /> <br />8/25/2004 <br />