Is Dutch Elm Disease Still in Nebraska?

The American elm tree, Ulmus americana, is a beautiful shade tree native to Nebraska. This tree was selected for planting along urban streets due to the tree’s ability to adapt to different soil conditions and for the wide, picturesque canopy that offered considerable shade.

Dutch elm disease, or DED for short, was first found in the U.S. in the 1930’s. It spread throughout the eastern U.S. and was officially confirmed in Nebraska in the 1960’s. Millions of elms have been killed by this disease and finding a mature American elm in Nebraska now can be quite rare.

While American elm is the most susceptible to DED, all other elms have some level of susceptibility and can still transmit and succumb to the disease. This makes DED a viable threat to elm trees in our state even today.

DED is caused by a small group of fungi that invade the vascular tissue of elm trees. The fungi plug the water-conducting tissues, or xylem. The tree tries to protect itself by sending compounds to the infection site to try and stop the spread. This can plug even more xylem making the condition worse.

The fungi causing DED can be introduced to an elm tree in several different ways mainly by bark beetles, root grafting, infected pruning tools and mishandling of infected wood material.

Adult elm bark beetles feed on small branches or twigs of elm trees. As the beetle feeds on an infected elm, the viable spores of the DED fungus attach to the beetle’s body or mouth parts. The spores on the beetle can then be passed to an uninfected elm while the beetle feeds. The

root of an elm tree can graft to another elm tree’s root when those roots touch. When this happens, the vascular system of both trees connects. An elm with DED can spread the infected to root system of an elm tree when grafting happens. Additionally, pruning can also spread DED infection. The infection can spread on the same tree, if making multiple cuts on the tree or to another elm tree if tools have not been sanitized. Wood that has been infected with DED, should be chipped or burned so as not spread the disease to healthy elms in the vicinity.

DED symptoms can include wilting leaves that turn yellow on one or more branches. These same leaves will then turn brown, dry and brittle. Vascular tissue underneath the bark of these branches will be streaked brown or gray. In cross-section, the branch will have a ring of discoloration. Trees can die within a few weeks or some trees can manage the disease for much longer even for over a year.

There is no cure for DED, though steps can be taken to limit the spread of the disease. Proper diagnosis, pruning and wood disposal along with preventative fungicide and insecticide treatments can slow the infection in areas where DED has been known to occur. For additional information on DED, contact the Nebraska Forest Service, your local extensions office or a trusted arborist.

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