Dutch Elm Disease

Dutch Elm Disease (DED) is caused by a fungus that is transmitted from one elm to another. Elms react to this disease by plugging its water conducting vessels in an attempt to stop the spread within the tree. The fungus is likely of Asian origin and was introduced into the U.S. in the early 1930s. The fungus is spread to other elm trees via bark beetles and also through naturally occurring root grafts between elm trees. Symptoms typically arise in late spring or early summer. The leaves on outer branches will curl (wilt) turn gray-green or yellow and then brown. These early symptoms are called ‘flagging’. Flagging is often isolated in one area of the tree in early stages, then the disease will spread to the entire tree. Trees prone to DED include the American Elm, Slippery Elm (also called Red Elm), and European Elms.

How to identify damages caused by Dutch Elm Disease

Early Signs

Trees with DED will exhibit flagging (wilting) of individual branches or in some cases the entire tree.
Wilted leaves will first often turn yellow on individual branches or sections of an elm tree – sometimes mistaken for seasonal color change.

Late Signs

The entire tree will be wilted and appear dead.
Any remaining brown leaves will fall and eventually the bark will start to separate from the tree and branches will begin to drop off.

Dutch Elm Disease Prevention

For Homeowners

Never prune your elm tree or have it pruned during the growing season. Bark beetles that can spread the DED fungus are attracted to fresh pruning wounds. Elms should only be pruned during the dormant season generally from October – March.
Observe your tree often during late spring and early summer thru August to look for early signs of flagging.

Dutch Elm Disease Prevention

For Professionals

Treat trees preventively with systemic fungicides.
Properly prune out infected branches, this needs to be done very quickly after observing any flagging to be effective.
Prune trees of dead wood in the dormant season when bark beetles are not active.

Dutch Elm Disease Treatment

Elm trees will need a trunk injection with a systemic fungicide every three years. Some trees may need treatment every two years.

Sanitation pruning of recently infected branches MAY limit the spread of the disease in the tree.

Dutch Elm Disease FAQs

Why is it called Dutch Elm Disease?

The early scientific work on the disease was done by Dutch plant pathologists.

Can I still plant elms in my yard?

Yes, there are now available hybrid elms that have good resistance to DED.

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