DUTCH ELM DISEASE
Dutch Elm Disease (DED) has returned. After 20 or so years of absence, we have yet to face its destruction again. DED, a deadly disease caused by a member of sac fungi and spread by Elm bark beetles. DED is responsible for thousands of Elm tree deaths here in the states.
History:
According to Denver Parks and Recreation Data reported 50 infested trees in 1969, then 12,000 by 1972. In 1984 the deaths declined, however not by triumph of treatment, but because there simply was no more trees left for DED to kill. Only 30% of Denver’s American Elm population survived after 15 years of the DED attack.
Since the outbreak some communities have established regulations against pruning Elms outside of dormancy. Open wounds made from pruning attract Elm beetles. These initiatives have kept DED to a minimal, however the threat is still very real.
Signs and Symptoms:
The first symptom is usually premature leaf color changing in summer months. Additionally, a section of the tree may look more withered and yellow then the rest. This will continue to spread and display more dieback of branches.
- Symptoms first appear in early – mid summer
- Clusters of leaves will turn yellow, then wilt
- Leaves will turn brown and fall off
- This will happen starting at the outside of the limb and move toward the main trunk
- Twigs sometimes turn downward
- Tree might display a mixture of healthy and diseased foliage
- Beetle galleries seen under bark
Dutch Elm Disease Movement:
As you can see in the diagram, there are two forms of DED movement, within the tree and through root graft. The transference of the infestation can be fast if not caught in its early stages.
Managing Dutch Elm Disease:
Reduce breeding site by prompt removal of dead or dying limbs or areas
- Branches should be removed immediately at any sight of infestation to prevent further spreading
- Trees with multiple infected limbs are advised to be removed completely
The use of preventative fungicide injections can protect trees from beetle infection.
- Fungicide injections can only be done by a trained arborist. Depending on the chosen fungicide, the treatment must be repeated every 1-3 years.
- Fungicides with the active ingredients thiabendazole and propiconazole are effective against DED.
