Nature Bulletin No. 569-A May 31, 1975
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
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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Update: June 2012