 What is Dutch elm disease?
Dutch elm disease is a water conduction blocking fungus that kills elm trees. It is caused by a fungus that is spread by the native elm bark beetle and smaller European elm bark beetle. The fungus clogs the water transporting vessels of trees causing wilting and flagging of the leaves which turn yellow and eventually brown which tend to be persistent on the tree. The fungus can be seen in the outer sapwood that becomes streaked with the dark brown fungus.
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Characteristic flagging leaves - early stage
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Yellowing leaves - secondary stage
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Brown persistent leaves - third stage
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Staining under the bark showing the fungal spores
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What is a native and European elm bark beetle?
The native and European elm bark beetle is an insect that carries the fungus that causes Dutch elm disease in elm trees.
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What can be done to prevent Dutch elm disease?
High value elms in parks and open spaces can be kept healthy by watering and fertilizing. Prune dead or dying branches immediately. Make sure to sterilize your pruning equipment between cuts using alcohol, bleach or any other sterilizing agent. There are pruning restrictions in the Dutch elm disease act that prohibits pruning elm trees between April 1 to
July 31. In addition it is illegal to store or transport elm wood for any other reason then disposal at a landfill designated to receive elm wood. The Insect Control Branch, in conjunction with Urban Forestry, control elm bark beetles, the carriers of Dutch Elm Disease, by spraying Dursban® Turf (chlorpyrifos) onto the lower 50 cms of elm trees on both public and private property.
Do not transport any type of wood as it is possible to transport pests into the City of Winnipeg. If you do not know what type of wood it is, leave it and do not transport it to your home.
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Tanglefoot banding is also an alternative in decreasing the overwintering success of the native elm bark beetle by preventing the adult beetles from migrating down the trunk of elms where they burrow into the bark on the lower trunk. To control the elm bark beetle, put bands on by late September, remain on the tree until the May long weekend. For information on how to band trees, please refer to the tree banding section of the cankerworm page.
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