Prevent Dutch Elm Disease

News Article
Dieback of branches indicating Dutch elm disease
To protect our elm trees from Dutch elm disease, pruning of any elm is prohibited from April 15 to October 15 in the City of Portland. Watch for signs of of Dutch elm disease.

Portland Has about 3,500 Elm Trees

Did you know that Portland has one of the largest populations of mature American elm trees remaining in the US?

Dutch elm disease is a destructive plant pathogen. It is caused by a parasitic fungus which affects elms trees.

One of the ways in which DED spreads is by the elm bark beetle which breeds, feeds and overwinters in elm wood. In infected trees, the spores of the DED stick to the beetles and are transported to healthy elms when beetles emerge to feed.

Pruning cuts and open wounds in elm trees attract the elm beetle, so elm pruning should not occur when the beetles are most active.

To protect our elm trees from DED, pruning of any elm is prohibited from April 15 to October 15 in the City of Portland.

Portland keeps DED in check by adhering to a strict management plan which includes:

  • Monitoring: Each summer, Urban Forestry monitors elms for visual signs of DED.  Suspected trees are tested.  
  • Removal: Infected elms are quickly removed and stumps are ground to reduce spread of the fungus through root grafting (the second way in which DED is spread).
  • Sanitation: After removal, wood is disposed by chipping, debarking or burying at approved wood disposal facilities. All tools used in removal are sanitized to remove spores of the fungus (human activity is the third way in which DED is spread). 
  • Inoculation: Elms in City parks are inoculated with a fungicide to protect against DED. Some neighborhoods also organize inoculations for their street tree elms. A Chemical Treatment Tree Permit is required before applying chemicals to City-owned trees.
  • Education: Urban Forestry serves as a resource for the public about DED, providing education and information.

Learn more about DED

Watch for Signs of Dutch Elm Disease

The photo above shows dieback of branches on an elm tree. The dieback is a symptom of Dutch elm disease (DED).

If you suspect DED on your trees, please contact or call 503-823-TREE.


City of Portland Urban Forestry

Manager of Portland's urban forest