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 DUTCH ELM DISEASE

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.