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Dutch Elm Disease Reported – Start Scouting Now (06/27/19)

The reports coming in now about wilting and dying American elm trees remind us that Dutch elm disease (DED) was first reported in Mandan fifty years ago and is now found throughout North Dakota.

The reports coming in now about wilting and dying American elm trees remind us that Dutch elm disease (DED) was first reported in Mandan fifty years ago and is now found throughout North Dakota. American elm, once common in cities, native forests and windbreaks, is our most susceptible elm. Siberian elm, commonly planted in windbreaks, is the most resistant but still can get the disease. DED is caused by a fungus which spreads from tree to tree via bark beetles and through root grafts. Elm trees infected with the DED pathogen by beetles show symptoms of wilting, curling, and yellowing of leaves on one or more branches in their upper crown. These symptoms can continue to spread through the tree for a few years before the tree finally dies. Elm trees infected through root grafts show wilting beginning lower in the crown and often die within the year.

Since elm bark beetle populations rapidly build up in dying elm trees and in dead elm wood with intact bark, one of the most effective ways to slow the spread of DED on a community level is to identify and remove this material within 2-3 weeks of noticing the symptoms. Waiting until fall or winter to do all the removals is not effective at slowing DED spread. Infected elm wood can be burned, buried, chipped, or debarked. Failure to remove DED-infected material immediately (within 2 or 3 weeks of identification) allows beetles to continue to spread the pathogen unchecked.

To prevent spread of DED by root grafts, roots can be severed by digging a 36-inch-deep trench all the way around the infected tree. In many communities, underground utilities may limit the use of this technique. The infected tree must still be removed immediately (within 2-3 weeks of noticing the symptoms). Before attempting any trenching, call North Dakota One call, (800) 795-0555, or 811, to mark utility lines.

 

Fungicide injections can be effective at preventing DED from infecting healthy trees. This should be done by a trained tree care professional. Fungicide treatment lasts about 3 years and is most effective when a community-wide sanitation program is in place where infected material is removed and disposed of promptly and properly (within 2-3 weeks).

When replacing the trees lost to DED, it is possible to replant DED-resistant elm trees along with a diversity of other well adapted trees. To learn more, see: https://www.ag.ndsu.edu/publications/lawns-gardens-trees/elms-for-north-dakota/f1893.pdf “Elms for North Dakota” includes a list of recommended elm trees.

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Lezlee Johnson

North Dakota Forest Service

Forest Health Manager

 

Joe Zeleznik

NDSU Extension Forestry Specialist

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