When the beetles emerge from DED-infested trees, they carry spores of the fungus on their bodies and migrate to vigorous elms to feed. A second way the fungus can be spread is by root grafts. Roots of adjacent elms often make contact and grow together, thus allowing the fungus to travel from an infected tree to a healthy adjacent tree. The disease results in wilting and yellowing of the foliage, followed by leaf death, defoliation and death of the affected branches. Wilting and yellowing of the leaves usually becomes visible about mid June and are most evident during July and August.
Brown streaks develop under the bark in the sapwood of infected branches.
This may be seen as a ring of discoloration when a diseased branch is cut or as dark streaks when the bark is peeled back from the infected branch. The most important step in control of DED is good sanitation. If proper sanitation practices are not followed, other control measures are of little use. Remove and dispose of all diseased elms and all elms killed or seriously weakened regardless of cause. Elm wood may be chipped so none remains with sufficient bark to serve as brood wood for beetles.