Date: April 1989 (Revised April 1995)
Source: NDSU Extension Service Horticulturist
Dutch elm disease is a severe vascular wilt that affects primarily American elm. The first symptom usually is a wilting of a single branch high up on the tree. The leaves rapidly turn yellow, then begin to fall. Within a few months the wilting spreads throughout the rest of the tree. Once the disease reaches the main trunk, the entire tree wilts and the leaves turn a bronzed color and hang on the tree for several weeks before they fall. This is the most frequently observed symptom pattern. It occurs when the Dutch elm disease fungus is spread by the elm bark beetle.
When several elm trees are close, so that their branches are touching, the roots will be grafted together. The Dutch elm disease may be transmitted from tree to tree through the root grafts. In this case, the entire tree wilts suddenly, beginning with the suckers along the base of the main trunk. The leaves are bronzed and hang on the tree for several weeks before dropping.
There is little hope of curing a tree that already has Dutch elm disease unless the disease can be detected when less than 5 or 10 percent of the tree is wilted. Control should focus on preventing spread to other American elm trees. Spread can occur through root grafts and by means of the elm bark beetle. To prevent spread by root grafts, trench between diseased and healthy trees, so as to prevent the passage of the disease through the root system. Make a second trench between the first and second healthy tree.
Use sanitation to prevent spread by means of the bark beetle. This means destroying all dead or dying elms with the bark still attached, as these are the breeding places for the elm bark beetles. It is essential to debark all elm firewood or else burn it up by April 1, which is the date that beetles begin to emerge from hibernation in the spring.
Additional information on this topic is included in the Extension bulletin PP-324, "Dutch Elm Disease," which is available at your county office of the NDSU Extension Service..
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