People often assume that all of our American Elms have been killed by Dutch elm disease. Fortunately, such is not the case. Though many have survived thus far, the number diminishes each year. We are still seeing examples of Dutch elm disease on American elms. Though American elms are the species often associated with this disease, red and some hybrid elms are also susceptible. Siberian elm (sometimes referred to as Chinese elm) and the true Chinese elm (lacebark elm) are considered resistant but not immune to the disease. However, we do have true American Elms that are naturally resistant. Our January 19 issue of this newsletter has an article on these cultivars. That issue can be found at: http://hnr.k-state.edu/extension/info-center/newsletters/2016/Jan19_2016_3.pdf
Early diagnosis can help save recently infected trees. Look for branches with leaves that have wilted and suddenly turned yellow to brown. Remove a portion of the branch and peel back an area of the bark.
If you notice brown streaking in the sapwood, you may have Dutch elm disease. Healthy bark is more cream-colored and the streaking is absent.
Suspect wood should be submitted to the diagnostic lab and control measures started immediately.
Dutch elm disease can often be controlled through the use of systemic fungicide injections, judicious pruning of affected trees and removal of nearby diseased elms. However, trees infected through root grafts with nearby infected elms or those in which the disease has reached the main stem cannot be saved. Therefore, preventative measures have a better chance of success and are preferred. Fungicides labeled for Dutch elm disease include Arbotect and Alamo. The Arbotect fungicide is preferred because it is the most persistent with a three-year interval between injections. A trained arborist should administer injections. These treatments are quite expensive. Check with your local arborist for current prices.
Megan Kennelly, one of our plant pathlogists, has a more detailed discussion of this disease in our Turf Blog. See http://blogs.k-state.edu/turf/dutch-elm-disease/ (Ward Upham)