2004-08-25 WS & CC Meeting - Laserfiche WebLink

Home Browse Search

. United States Department of Agriculture Forest Service __mlVea NA-PR~ Dutch Elm Disease (OED) and the American Elm For decades the American elm was one of our most treasured trees, gracing streets and parks of many cities with beautiful form and dense foliage. The American elm was particularly well suited to urban sites because it grows quickly, is long-lived, and is tolerant of compacted soils and air pollution. However, in most communities Dutch elm disease (OED) killed a significant number of our American elms and threatens those that remain. By wisely choosing how we manage our urban elm resource, we can reduce the risk of remaining elms becoming diseased. What is DED, and where did it come from? OED is one of the most destructive shade tree diseases that affects elm trees. The disease kills individual branches and evootually the ootire tree within one to several years. A fungus and an insect are responsible for OED developmoot. The fungus was introduced to the United States on diseased logs from Europe in the 1930's. This row of elms was killed by OED. which moved through the root systems from one lree 10 the next. What causes the tree to die from DED? The OED fungus grows and reproduces in the water conducting parts of elm branches and stems. The fungus blocks water movemoot to tree leaves which causes the leaves to wilt and turn brown. How does the DED fungus get into the tree? The fungus needs help from insects, the elm bad< beetles. Elm bark beetles use weakooed and diseased trees to reproduce. Beetle offspring emerge from diseased elms and fly to healthy elms to feed. However, before leaving diseased trees, spores of the OED fungus (which are like tiny fungus "seeds") attach onto them. When these fungus-infested beetles feed on healthy tree branches, they make small wounds in the wood, and the fungus ooters the branch directly through these wounds. Once the fungus is in an elm tree, it can move through the root system of a diseased tree into the root system of adjacoot healthy elm trees. It can do this because roots of elm trees growing close to each other frequootly join or graft to each other. Arrow points out minor OED symptoms (yellowing leaves on a single branch) in an American elm.