Dutch Elm Disease
Dutch elm disease is caused by a fungus, which blocks the water-conducting tissue of the tree, and is spread by two species of bark beetles. These beetles feed, breed and over-winter on the wood of both live and recently killed elms.
Initial symptoms include discoloration and wilting of foliage on small branches high in the tree crown. The wilt symptoms spread until, eventually, foliage throughout the crown wilts and yellows, and the tree dies.
Dutch elm disease also spreads through root grafts. Trees infected in this way normally show massive wilt symptoms throughout the tree crown and die rapidly.
Another symptom is the formation of brownish-red streaks in infected sapwood, either on recently wilted branches or in the main trunk. Call your county Extension Office to learn more about how and when to take a branch sample. If warranted, the Extension Office will forward the sample to the diagnostic laboratory.
So what can you do to help control the spread of Dutch elm disease? Sanitation is the key. Homeowners can help by identifying and removing dead, dying, or weak elm wood with the bark still attached. This means all elms. If more than 25 percent of the tree crown is infected, the tree cannot be saved. Remove the tree as soon as possible. Elm wood should be buried, burned or chipped at once. Do not place elm wood in firewood piles, as this is the major source of disease fungus and beetles.
For information about other protective techniques such as trenching, fumigation, and preventive and therapeutic fungicide controls, contact your city forester or the County Extension Office.
If your American elm shows wilting symptoms, it is very important to find out why quickly. An early diagnosis of Dutch elm disease is crucial for two reasons. First, it may be possible to save the tree. Second, proper control actions will prevent the spread of the disease to other native American elms.