Ash Tree Decline

Disease, adverse weather conditions, and poor cultural care affect the overall health of ash trees. Repeated events wear down tree defenses causing slow or abnormal growth, branch dieback, and tree death. Three common diseases causing branch dieback and tree death include ash yellows, verticillium wilt, and cankers.

Ash yellows typically causes the formation of what looks like witch's brooms on the main trunk. These brooms lack a central stem and appear as a yellow-green proliferation of growth. Witch's brooms are often confused with salt spray damage or natural sprouting on healthy trees. To identify salt damage, simply determine whether the tree was exposed to salt spray.

Verticillium wilt typically causes wilting and tree death. Branches in the upper crown or along one side of the tree often wilt first, as leaves on infected branches turn brown from the leaf's edge inward. Verticillium is often confused with winter injury, stem girdling roots, and drought stress. These factors also cause drought-like symptoms. Identifying verticillium is difficult and usually requires a professional diagnosis.

Canker diseases typically cause swollen, sunken, or target-shaped wounds to develop randomly on the branches or the main trunk. These wounds often girdle that portion of the tree causing it to die. Canker diseases are easily confused with mechanical injuries.

Unfortunately, there are no effective treatments available for control of these diseases. As a result, the only beneficial control strategy is to improve tree health. Trees should be watered during dry periods, mulched, properly fertilized, and protected against soil compaction. Severely affected trees may not recover.

For more information, call your local Extension office or visit the Yard and Garden web site at www.extension.umn.edu.

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