Siberian Elm Diseases
Siberian elm is a large tree, reaching heights of 60 or 70 feet. It is often found growing along streams in the U.S. Although Siberian elm is resistant to Dutch elm disease, which is often fatal to other elm species, it is susceptible to many other diseases that affect elm. Does this Spark an idea?
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Cankers
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The most common cause of death in Siberian elms is Botryodiplodia canker. Drought-stressed Siberian elms are very susceptible to the disease. The main symptom of Botryodiplodia is the presence of water-soaked, soft, reddish brown-to-black cankers on the bark of the tree. The cankers may eventually expand, surrounding the branch they are on, resulting in wilting foliage and death of the branch. Large patches of bark may loosen and peel. Tubercularia cankers also occur in Siberian elm, developing on the trunk, branches and twigs of affected trees. Dead branches with dead leaves still attached may be a sign of the presence of the canker. The surface of the bark starts as reddish-brown but eventually becomes brown to black as it dies.
Fungal
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Verticillium wilt, caused by the fungus Verticillium alboatrum, causes the leaves of Siberian elm to take on a dull appearance in the early summer and to begin to drop without wilting. The symptoms may appear only on branches on one side of the tree or on the entire tree. When an affected branch is cut off, a ring of discolored wood can be seen, and if the bark is peeled back, discolored streaks can be seen in the wood. Black leafspots, another fungal disease that affects Siberian elm, is caused by Stegophora (Gnomonia) ulmea. Leaves on infected trees have small grayish spots on the upper leaf surface which are sometimes surrounded by a yellow halo. Eventually, the spots become black and thickened, and the leaves may turn yellow and fall prematurely.
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Bacterial
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Wetwood is a bacterial infection that causes discoloration of the wood and wounds or cracks; these tend to ooze sap, a condition termed "slime flux." The slime flux on the outside of the tree results when internal pressure in the wood, caused by growth of the bacteria in the heartwood of the tree, forces out the sap. This bacteria-ridden sap encourages the growth of yeasts and molds that produce a foul odor. Most Siberian elms eventually become infected with wetwood; a tree can live with the disease for decades. Damage is mainly aesthetic.
Management
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Strategies for controlling diseases of Siberian elm include pruning out and destroying infected branches in the case of wilts; raking up leaves in the fall and burning, composting, or burying in the case of leaf spots; and directing flux away from the trunk of an elm affected by wetwood using a tube. A fungicidal spray, such as a fixed copper fungicide, may be used on elm black leafspot. Preventative measures include avoiding planting a Siberian elm in an area where Verticillium fungus may be in the soil to prevent Verticillium wilt and avoiding unnecessary wounds to the elm to prevent cankers, especially in elms where active cankers are present. Keeping trees well-fertilized and treating insect infestations immediately will help ensure the tree's vigor.
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References
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