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Bleeding of Elm Trees (Elm Wetwood Disease)

Source: NDSU Extension Service Horticulturist

Elm trees in North Dakota frequently bleed or ooze sap from wounds, cut branches and crotches. This ooze causes the bark that it touches to turn a lighter color than the rest of the bark. When this sap drips onto the grass, it kills the grass. This is a bacterial disease that is found in almost all elms in our state, although some trees are more severely affected than others. The wetwood bacterium lives in the wood of the tree, and ferments the sap. This fermentation produces gas. Tremendous pressures build up inside the tree, causing the sap to ooze from wounds or cracks. The sap is toxic, and retards or prevents healing.

There is no control for this disease. In the past, it was recommended that a drain pipe be placed in the tree directly beneath the bleeding area to reduce pressure in the tree, and carry the sap away from the tree. Recent research, however, has shown that these drains can damage the tree. Therefore, the installation of drain pipes is of doubtful value.

If you have further questions, please contact your county office of the NDSU Extension Service.

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