Diseased Trees


Two well-known diseases continue to be a threat in the City. Dutch elm disease and Oak wilt are still infecting trees throughout the city.  Watch for signs of the disease in your oaks and elms.

Dutch Elm Disease

Dutch elm disease is a very common problem throughout the city each year. Tell-tale signs of the disease include “flagging,” where an entire branch of leaves will turn yellow and then brown creating a sort of “warning flag” in the tree canopy.
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Dutch elm disease can kill an elm very quickly during the summer and poses a threat to neighboring elms as well.  According to city ordinance, the property owner must remove infected trees within 20 days of notification by the city. The disease can be controlled through proper sanitation measures and chemical treatments.

Elms are great shade trees. There are now disease-resistant varieties available at local garden centers.

Oak Wilt

While not overly prevalent in Chanhassen, oak wilt has been diagnosed on several trees in throughout the city. Watch your oaks, particularly red and pin oaks, each summer for branches full of dead, brown leaves and/or a rapid decline in health. If you have an infected tree that is diagnosed very early, there may be a chance to save it through pruning and chemical treatment.  Infected oaks pose a serious threat to surrounding oaks and must be removed within 20 days to prevent the spread of the disease. 
Don't Prune in April, May and June.
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Bur Oak Blight

Bur oak blight is often mistaken for oak wilt. This fungal disease only affects bur oaks, causing their leaves to form wedge-shaped dead areas, brown leaf veins, and dead leaves that persist through the winter.
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Bur oak blight is not fatal to bur oaks, but repeated infections over several years can weaken the tree leaving it vulnerable to fatal attacks by two-lined chestnut borer or armillaria root rot.


The city provides free diagnosis of tree diseases. If you suspect your elm or oak may be infected or have other trees in your yard that are unhealthy, contact the Environmental Resource Specialist.