Dutch Elm Disease is one of the most destructive shade tree diseases in North America. It affects American elms and kills individual branches, then eventually the entire tree over the course of one to several years. It can also spread to nearby trees. At Arbor Aesthetics, we strongly recommend NOT trimming your elm tree between April and October when the trees are leafing. How is it contracted?
The DED fungus was first introduced to the U.S. on diseased elm logs from Europe prior to 1930. A tree can contract this fungus by way of:
Photo by Brian Olson, Oklahoma State University.
Elm bark beetles. They are attracted to stressed, dying or dead elm wood to complete the breeding stage of their life cycle. Eggs are laid into the bark, then once hatched, the larvae feed on the inner bark and sapwood. If the DED fungus was present in that tree, the fungus produces sticky spores that stick to the adult beetles as they emerge from the tree. The adult beetles then visit healthy trees and transfer the spores.
Grafted roots. Roots of the same or closely related tree species growing nearby often cross each other in the soil and eventually fuse to each other. A tree that becomes infected by way of grafting can die rapidly, as the fungus is carried upward in the sapstream.
What are the symptoms?
DED is a vascular disease, meaning it affects the way a tree is able to conduct water. Because water cannot travel down to the roots, leaves will wilt, yellow and drop. The photo to the right shows the beginning symptoms of DED.
How is it treated and prevented?
The key to conquering DED is early detection and prompt treatment. If you suspect any of your elm trees are suffering from DED, call Arbor Aesthetics and our certified arborists can discuss possible treatment options.
Pruning. Careful pruning of infected branches can prevent the disease from spreading down the tree. One of our certified arborists will be able to tell whether or not pruning alone will be an adequate treatment or if injecting a fungicide is necessary.
Injecting fungicide. Certain fungicides are effective in protecting elms from infection via the elm beetle. It is expensive, however, and must be repeated every one to three seasons and may also pose a risk to the health of the tree.
Courtesy of Cheryl Kaiser, University of Kentucky.
Disrupting root grafts. Large trees within 25-50 feet of each other are likely to have root grafts. Breaking these grafts between injected trees and adjacent healthy trees is an important means of preventing movement of the fungus.
Planting resistance species. There are many hybrid elm crosses and species of elm that have a high tolerance or resistance to DED. Some examples are the Princeton Elm, the American Liberty Elm, the Valley Forge American Elm, and the New Harmony American Elm.
Diversifying. Incorporate a variety of tree species in your landscaping.
Considering the spacing. Planting multiple elms too close to each other makes them susceptible to the spread of DED. Alternating an elm with another species can prevent or slow down the infection.
Practicing sanitation. To be completely effective in interrupting the spread of the disease by elm bark beetles, stems and branches of DED infected trees must be de-barked, destroyed, or utilized before the bark beetles emerge. During the growing season, removal should be completed within 2 to 3 weeks of detection. During the dormant season, removal should be completed before April, when overwintering beetles may begin to emerge. Wood can be destroyed for chipping, burning or burying. Many communities have regulations on the removal of diseased elms and the storage of elm firewood.