First seen in North America some ninety years ago, Dutch elm disease has wiped out millions of American elms across the nation. Early federal campaigns failed to halt the spread of the disease which is caused by several species of fungus and is spread by the elm bark beetle. Female beetles lay their eggs in weak or dead elm trees. The eggs are laid in gaps between the bark and the wood. The beetles bring with them fungal spores on their body and these spores multiply as the eggs mature and are then spread by the emerging beetles. Healthy trees too are infected by the beetles when they feed on new growth twigs. Early identification and intervention is the key to saving infected trees.
Symptoms: While positive identification can only be done in lab cultures, infected trees will show signs of wilting leaves on one or more branches. The leaves may curl and fall early. A dark discoloring may be seen on affected branches.
More information: University of Minnesota Extension, Ohio State University Extension, USDA Forest Service