Dutch elm disease, photo by R.S. Cameron, International Paper.
American elms have been the victim of a decimating disease known as DED or Dutch Elm Disease. However, there are a few that linger and remain gracing our city streets with their majestic, arching form. Many elms are mistakenly identified as American, however, there are many other “weedy” elms which have naturally inhabited our urban landscape. Due to the incredible interest in these trees, plant breeders have developed resistant American Elms which are showing excellent results. Unfortunately, many of those trees proved to be susceptible to other diseases such as Elm Yellows.
Providing that the tree has been identified as an American elm, proper management is required to maintain its health and vigor to provide a sustainable tree in the landscape. Strategies include:
Sanitation: Quick removal of diseased trees and symptomatic branches is necessary in managing this disease. Removal of the damaged parts reduces breeding sites for the elm bark beetle and removes the fungus from the vicinity. Branches with "flagging" symptoms should be removed making a cut well behind (5-8 ft) any visual symptoms.
Pesticide Applications: Insecticides to kill bark beetle vectors: attempt to control the insect vector population by applying an insecticide. Timing of the application may depend on the type of insecticide you have selected. Some insecticides may target the spring feeding sites while others target the overwintering sites and should be applied during late autumn. Use of this management option should be considered carefully. It is difficult to attempt control over this beetle population due to the timing factor, the complete coverage issue, expense and pesticide exposure. Preventative fungicide injections: There are effective fungicides capable of protecting elm trees from infection, but this method of management should be considered carefully. Fungicide injection must be performed by someone trained in the technique and may be expensive. Protection lasts 1-3 years, and then must be repeated. In addition, some researchers are concerned that repeated wounding of the tree (by drilling holes) for the injection may open trees to decay. If there is concern for infestation, it is critical to contact a reputable tree care company specializing in good plant heath care. Always contact an International Society of Arboriculture Certified Arborist to help insure best practices. For more information on DED and management strategies click on the links below.
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Lindsey Purcell, Urban Forestry Specialist
Department of Forestry and Natural Resources, Purdue University