Dutch Elm Disease
Ophiostoma ulmi & Ophiostoma novo-ulmi
What is Dutch Elm Disease?
Dutch Elm Disease (DED) is a vascular disease affecting all species of elm. However, our native American Elm (Ulmus americana) is most severely affected by this fungus. Although no specie of elm is immune to DED, cultivars of the American Elm have been produced that are resistant to DED.
American Elm leaf
Identifying Dutch Elm Disease
The most apparent symptom of DED is a characteristic wilting of leaves. These wilting leaves will first turn yellow and hang from the branch (much like a flag without a breeze). The “flagging” leaves will subsequently turn brown and prematurely drop. Often fallen leaves can be found on the ground below infected elm trees, in the late spring and summer months, particularly in hot/humid weather.
In the early stages of infection, flagging is typically isolated to a single branch of the tree. In later stages of infection branch dieback will extend into a larger portion of the tree’s canopy, until eventually the tree will succumb to the disease.
Characteristic wilting leaves on elm trees known as “flagging”, are indicative of Dutch Elm Disease. Flagging appears in hot weather during the growing season, before autumn leaf drop would set in.
Tunnels from the Elm Bark Beetle leave a unique starburst pattern.
Dutch Elm Disease in Highland Park
As trees infected with DED pose a significant likelihood of passing the disease on to adjacent Elm trees, Highland Park City Code requires the removal of DED infested elm trees on private property. This limits the chance that the disease can spread to other healthy Elms on private or public property. Each year the Forestry Section monitors public and private properties for signs of trees infected with DED. Once identified, property owners are notified of the infestation.
Despite the presence of DED, Elms are an important component to the urban forest of Highland Park. DED resistant varieties of Elms are routinely incorporated into the Highland Park’s tree planting programs.
Preventing Dutch Elm Disease
Most often, the fungus that causes DED is transmitted from an infected tree to other elms by the Elm Bark Beetle. This insect will pick up the fungus after hatching inside an infected Elm or infested firewood and will move on to healthy Elm trees to feed. In the process, infesting a new host with the disease.
Although healthy trees can be treated to prevent DED, there is no cure. Once a tree has been infected, the fungus can persist. Trunk Injection of fungicide and removal of infected branches is the best method to preserve a tree with DED, if diagnosed early on. If you suspect that your tree may be infected, contact a Certified Arborist to discuss your options. If you cut down a tree due to DED, do not store logs from infected elm trees near healthy elms on your property or near your neighbor’s elms. The disease can still spread once the tree is cut down.