Forest Preserve District of Cook County, Illinois
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The Dutch Elm Disease
Nature Bulletin No. 411-A   March 20, 1971
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

The American elm, far and away our most popular and important shade tree, is facing its most threatening enemy, the Dutch Elm Disease. A large part of them seem to be doomed unless up-to-date methods of control are used. In New England the appearance of whole towns has been changed by the loss of gigantic elms along entire streets. This same havoc is being repeated in most eastern states and, now, as far west as Missouri. The first diseased tree in Illinois was found downstate fifteen years ago. Since then, the infection has spread over most of the state, reaching the Chicago region in 1954.

The Dutch elm disease attacks all kinds and all ages of elms in varying degrees, but our American Elm is most susceptible. The Siberian and Chinese elms are quite resistant. A few years ago, in Holland, a single surviving elm was found among a grove which had been wiped out by the disease. Named the Christine Buisman Elm after the woman scientist who discovered it, a variety grown from this tree shows almost complete immunity.

The cause of the Dutch elm disease, a fungus that grows like bread mold in the sapwood of the tree, was first found in Holland in 1921. Within the next few years it was recognized in dying elms over most of central and southern Europe. In America, the first known case was found in 1930 at Cleveland, Ohio, where, apparently, it arrived in a shipment of elm logs from Europe. In 1932 it appeared in New Jersey and soon after in New York, Connecticut and Maryland. Between 1933 and 1947 the federal government spent 25 million dollars in an attempt to wipe out the disease, but failed. In Illinois, the Champaign-Urbana community gives an example of its uncontrolled spread. A single diseased tree was found there in 1951, eleven in 1952, 164 in 1953 and 694 in 1954.

The microscopic spores of the fungus are carried from diseased trees to healthy trees by two kinds of little brown eighth-inch-long beetles that burrow beneath the bark. The worse of the two for spreading the infection is the European elm bark beetle which had begun to spread through the eastern states twenty years before the Dutch elm disease arrived. The adult beetles emerge from elm wood in spring and fly to other elms, usually less than 500 feet away, but sometimes are carried a mile or two by winds, There they chew into the crotches of twigs and small branches, and feed on the living wood which they infect with spores of the fungus rubbed off of their legs and bodies. These beetles lay their eggs and the young grow up under the bark of injured elms, elm logs, or dead branches. The other beetle is native to America and it does not spread the disease so rapidly.

Another way for spreading the infection is underground through root grafts that connect the roots of one elm to those of its neighbor. Such a graft allows sap carrying the fungus to pass from one to the other in a subterranean chain reaction often wiping out a whole row of elms along a street. Frequently, large trees die the same year that the first symptoms appear but they may survive several years, The most reliable symptom is brown streaks in the sapwood just under the bark but, for positive identification, laboratory tests are necessary.

Control measures are aimed at the beetles that carry the spores of the Dutch elm disease. Their breeding places should be destroyed by prowling dead and dying branches from healthy elms, by removing all dead or dying trees, and by burning all elm wood with bark on.

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