Elm phloem necrosis.—This is a virus disease of American and 
winged elms (702). It occurs in the Midwest in an area bounded 
by latitudes 30° and 40° North, and by longitudes 80° and 100° 
West. The virus is transmitted by the white-banded elm leaf- 
hopper, or through root grafts of trees growing close together. 
The insect sucks up the virus while feeding on the sap of a dis- 
eased tree. Later, the virus is transmitted when the insect feeds 
on a healthy tree. This leafhopper is widely distributed in eastern 
United States. 
Foliar symptoms of elm phloem necrosis vary but are some- 
what similar to those produced by drought, girdling, and certain 
other tree diseases. Symptoms may first appear on a single 
branch or a portion of the top; usually, there is a gradual decline 
of the tree. In large trees, there is usually a slight scarcity of 
foliage in the top or at the outer tips of branches. This is followed 
by a scarcity of foliage throughout the crown. The leaves turn 
yellowish-green, then yellow, and some on the lower suckers be- 
come dry and brown. Defoliation follows soon thereafter, and the 
tree dies. This occasionally happens within 3 to 4 weeks but it 
usually requires a year or a year and a half. Before the tree dies, 
a typical discoloration of the phloem develops. In large trees this 
discoloration is usually found only in large roots and the lower 
part of the trunk. In most small trees, and occasionally in large 
ones, it may be found in the upper part of the trunk and occa- 
sionally in branches. The discoloration (fig. 205) is at first yellow. 
Later, it turns to “butterscotch” and often contains scattered 
dark flecks. Still later, the phloem becomes brown and necrotic. 
Moderately discolored phloem has a faint odor of wintergreen, a 
F-520108 F-519951 
FIGURE 205.—Typical discolo- FIGURE 206.—Shade tree elms killed by 
ration of the phloem of an phloem necrosis virus. 
elm tree infected with elm 
phloem necrosis. 
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