Dutch Elm Disease
Dutch Elm Disease
Dutch elm disease is a vascular wilt that killed nearly all American elm trees in the United States, except where susceptible trees were isolated far from others of their kind. American elms as street trees exist today only in municipalities that have a monitoring and control program. The Siberian and Chinese elms and the hybrid elms are resistant to the disease.
Symptoms: Wilting, yellowing foliage and leaf drop first occur on one or a few branches. Then the entire tree may wilt and die in a few months to a few years.
Cause: Bark beetles that feed in the branch crotches of elm trees and burrow tunnels and lay eggs in dying or dead elm wood carry the fungus that causes the vascular wilt disease. Beetles generally are attracted to stressed trees rather than healthy trees. Controlling the beetles may help control the disease. Quickly destroying dead elm wood and dying trees and keeping healthy trees vigorous helps to limit the spread of the disease.
Control: Prune out infected branches immediately. When pruning, cut well below the area showing symptoms -- at least 6 feet below the brown vascular discoloration on the wilted branch. The pathogen usually is a distance beyond the symptoms. Systemic insecticides and fungicides have not been proven fully effective. Proper injection of Arbotect 20S once every three years has protected elms in university trials. Closely planted trees should be treated to remove the chance of root grafting. This is best done by passing a root cutting blade, 2 feet deep, midpoint between the trees. This severs root connections between trees. Alternatively, a soil fumigant can be placed at an appropriate concentration in holes 2 feet deep and 8 inches apart, along the midpoint between two trees to kill intermingling roots.
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