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.