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Dutch Elm Disease

Dutch Elm Disease (DED) poses a serious risk to the health of Elm trees.  It is caused by a fungus that can be carried on the bodies of Elm Bark Beetles who fly to stressed or injured elm trees, spreading the infection as they go. It is most often introduced into a community through the transport of fire wood. DED does not affect tree species other than elm.

What are we doing to prevent the spread?

In early August 2020, two cases of DED were identified in Lethbridge. Since then, the City of Lethbridge has been working with Provincial and Federal agencies to assess the scope of the infection and to develop a response strategy. This began with the immediate removal and safe disposal of the infected trees. The City is working to map the Elm trees, assess their condition and look for additional signs and symptoms of DED. There have been no confirmed cases of DED since August 2020.

Elm trees can be distinguished from others by their oblong, serrated leaves and distinctly vase-shaped trunk structure.

What is an Elm brochure
Stop Dutch Elm Disease Brochure

Elm trees are subject to a number of stressors in southern Alberta including European Elm Scale, Elm Wilt fungus, drought conditions and rapid changes in weather. As such, the threat of Dutch Elm Disease remains real.

Elm trees make up a significant and important portion of the Lethbridge Urban Forest with nearly 6000 public elm trees, and an estimated 5000 private trees. There are more than 750,000 elm trees throughout the province of Alberta.
Accordion Answer

Signs of Dutch Elm Disease vary by season but generally consists of the following symptoms:

  • In spring – trees may have a few branches with smaller or no leaves on them.
  • In early summer – green leaves may start to droop, curl or wilt. Some will turn brown but will remain attached to the branches.


  • In late summer – leaves will turn yellow and droop, this is a distinct characteristic of DED known as flagging. Yellow leaves may fall prematurely, and succulent branches on the stem wilt and turn brown.

  • Dark brown streaking in the outer sapwood is visible when the bark is peeled away on a small branch.

Elm bark beetles are hard to detect as they are very small, approximately 3.5 mm in length and make holes smaller than the diameter of pencil lead in the bark. The beetles which spread the fungus live, reproduce and overwinter in live or cut elm wood, therefore it is illegal to keep elm wood.

The beetles will travel to nearby elms to reproduce and inadvertently spread the fungus, perpetuating the infection. American elm may succumb to DED within weeks of initial infection.


Properly identify the trees on or near your property. If you don't have elms, you can rest easy. Check online or with your local arborist for help identifying your trees.

If you do, ensure your elms are properly cared for:

  • Do not prune them between April 1 and September 30

  • Water your elm specifically every week or two throughout the spring until mid-August. Elms require a watering schedule that differs from the requirements of your lawn.

  • Give the tree a good thorough watering before the fall frost as well as this will help it stay healthy through winter. 

It is illegal to keep, store or transport elm wood for personal use. Stored elm wood is the ideal breeding environment for elm bark beetles.

Check your trees regularly in spring and summer, chances are that changes to your elm are not Dutch Elm Disease, but there are a number of threats to elm trees out there and its always best to detect issues and illness in trees as early as possible.


We are carefully monitoring insect populations, including beetle traps and other detection methods.

There are a number of products registered in Canada for use as injection treatment applications to help manage DED. These are most effective as a preventative measure in healthy trees. Homeowners may choose to have their private trees evaluated and possibly treated by a professional tree care company. Arborists using any chemicals to inject trees must hold a valid Alberta pesticide applicator license.

The treatment for DED is time-sensitive, and infected trees must be removed as soon as possible. Tree material from the infected elms is to be immediately burnt or buried. 


The City of Lethbridge has been monitoring tree pests and insects for many years. Our Urban Forestry department uses insect traps to detect and monitor populations of a number of possible invaders including elm bark beetles and other harmful insects that pose threat to Lethbridge's urban forest health and the security of all trees in the region. Elm bark beetles collected are sent away to provincial or federal labs to confirm the species as a potential indicator of the DED fungus. 

The Urban Forestry department is highly trained in tree health evaluation and complete visual inspections of all trees within the City of Lethbridge as part of their daily procedures. Ailing or wilting trees are noted quickly and further inspection occurs. 

The City of Lethbridge also abides by the provincial pruning ban, which strictly prohibits pruning of elm trees between April 1 and September 30 each year.

  • This is the time where the elm bark beetles are most active and seeking weak or stressed trees to infest.
  • Creating open cuts or wounds by pruning attracts the bark beetles, increasing the risk of infection.

Lethbridge residents are encouraged to not transport firewood of any sort, as the wood may be a vector for DED and other harmful tree pathogens or insects.


​Leaf Shape

  • ovate shape
  • vibrant green
  • clearly serrated edges



  • braided appearance with deep grooves
  • silvery brown
  • leafy



  • Trees are distinctly vase shaped
  • Upward reaching branches


Check out STOPDED.ORG for more information about Dutch Elm Disease. 
If you think that an elm tree on or near your property has Dutch Elm Disease or European Elm Scale,
please contact 311.

For more information

Online: Submit a service request
Phone: 311 or 403-320-3111 (if outside of Lethbridge)
Address:  City Hall, 910 4 Avenue South, Lethbridge, Alberta, T1J 0