Forest Preserve District of Cook County, Illinois
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DED
Nature Bulletin No. 569-A   May 31, 1975
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

DED
Dutch Elm Disease is the most deadly and destructive of all the diseases that attack shade trees in the United States. The abbreviation "DED" is appropriate because an elm infected with it is doomed. There is no cure. Although the Asiatic species of elms and two European varieties seem to be somewhat resistant to this disease, no species or variety or hybrid is immune. The American elm -- by far our most popular and magnificent shade tree -- is extremely susceptible.

Shortly after the end of World War I, an unusual number of elms were dying in Rotterdam, Holland. In 1922 the cause was identified as a fungus, possibly brought there from Asia, that grows, like bread mold, beneath the bark of elms. Within 10 years the disease had spread over almost all of Europe. In 1950 the first known case of it in America was found at Cleveland, Ohio. Shortly after, it appeared around New York City, brought in by a shipment of choice elm logs from France. DED is now rampant from New England and the mid-Atlantic states to Kansas, from Michigan and Wisconsin to Tennessee, and in southern parts of the Quebec and Ontario provinces in Canada.

In the Chicago region, the first infected trees were discovered in 1954 -- one in Highland Park and one in Markham. In 1971 we issued Bulletin No. 411-A describing DED and the tiny elm bark beetles that carry it from tree to tree. That year 70 cases were found in Cook County, 6 of them in our forest preserves. Since then our foresters have waged a ceaseless war on these beetles and used all feasible means to prevent the spread of the disease. Despite this, 32 elms in the forest preserves became infected in 1956, 514 in 1957, and 9, 884 last year.

The first symptom on an infected elm is a rapid wilting and curling of the leaves -- usually on one or more branches in the upper part of the tree. Then they become yellow, finally brown, and drop off. The bare twigs, when peeled, show brown streaks in the outer sapwood. However, these symptoms are similar to those caused by some other diseases. Positive identification can be obtained only by sending samples of infected twigs to a plant disease laboratory.

If the verdict is DED, then the tree should be cut down immediately and totally burned. Also, all elms within at least a 500-foot radius should be sprayed thoroughly with an insecticide, to kill the bark beetles that chew into crotches of twigs or small branches and infect them with the deadly fungus. That may be applied with a hydraulic sprayer but many experts recommend a mist blower, maintaining that it provides better coverage. The battle against DED is not hopeless. Adequate control programs in several suburbs of Chicago and the Forest Preserves have held the losses each year to less than two percent of their total number of elms -- about the same as normal losses from natural causes. Those community-wide programs combine three principal jobs; scouting surveys, sanitation measures, and protective spraying.

Scouting detects the infected trees and all potential homes for bark beetles. Sanitation measures include the removal of infected trees, pruning of dying or recently dead branches, and destruction of other breeding places. Spraying is applied to all healthy elms.


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