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Dutch Elm Disease Information

Tree populations in Saskatchewan are subject to numerous stresses. Currently the most serious threat comes from Dutch Elm Disease (DED), a deadly disease of American elm trees.

  • Cause: a fungus under the bark of infected elms.
  • Carrier: elm bark beetles that feed on, and breed in elm bark.
  • Victim: American elms, our most magnificent shade tree.
  • Symptoms: Leaves that wilt, curl up and turn brown in summer.
  • Control: Frequent pruning to remove dead wood, immediate removal of dead elms and careful disposal of prunings and firewood.

How Does Dutch Elm Disease Spread?

Elm bark beetles spread the disease along natural corridors of American elms, such as the Saskatchewan, Qu'Appelle, Souris and Frenchman river valleys. Eventually they reach a community like Prince Albert or Saskatoon. Carrying the fungus on their bodies, the beetles infect elms as they feed. DED kills the tree and the beetles are forced to find other elms. These new elms will in turn die and the cycle continues.

People spread DED by transporting infected wood. By this means DED can strike your community overnight. For this reason it is illegal to transport or store elm firewood in Saskatchewan.

How can we protect Saskatoon from Dutch Elm Disease?

Saskatoon is almost the last major city in North America that has a significant population of American Elms and no DED (until July 2015). American elms have no resistance to DED, so early detection is essential to prevent an outbreak. We are surrounded by sites that have active disease. It is only a matter of time before we have to battle DED in our city to save the 100,000 elms that provide charm and cool summery elegance to our streets.

Be aware if one of your elm trees suddenly has wilting leaves on one of its branches.

  • Flagging is a common early sign of Dutch elm disease noticeable when the weather is hot and dry.
  • Other diseases also cause wilting, reducing the overall health of the tree.
  • For images of diseased elms, go to this page from the Gov't of Alberta.

What should you do, if you see an elm tree with a wilted branch?

  • Contact Saskatoon City Hall (306-975-3300) or the Ministry of Environment 1-800-567-4224.
  • The city will send a crew to remove the branch, and have it diagnosed. You do not have to do this yourself, and there is no cost to you. It is far less expensive to do this than to deal with tens of thousands of dying elms.
  • You might be preventing a catastrophic outbreak of Dutch elm disease.
Do not prune elm trees between April 1st and August 31st.
  • Elm bark beetles are most active at this time and they are attracted to the open wounds created by pruning, which are prime infection sites.
  • There may already be spores in the air.
  • During the period when pruning is prohibited, new cuts often ooze sap that can trap spores, as well as attract beetles which might be carrying DED as well.
Remove dead elm branches, and have them burned or buried.
  • The fungus can grow on dead wood, and produce air-borne spores.
  • Do not bring elm logs into the city for firewood – it is illegal!
  • Logs may have fungal spores or overwintering beetles or both.

What To Do If You Suspect DED

Early detection is a critical component in fighting Dutch Elm Disease. Early symptoms of DED appear from the latter half of June to the middle of July. Leaves on one or more branches may wilt, droop or curl. They then turn brown and typically remain on the tree. Infections later in the summer result in drooping leaves that turn yellow and fall prematurely. In all cases the infected branch is stained brown or bluish brown.

As DED can be confused with other diseases (see next column), it is important that the infected wood be tested for the specific fungus. In Saskatoon, the city will send qualified personnel to take a sample (call 306-975-3300). If you live in a rural area call 1-800-567-4224 or you may take a sample yourself and follow these directions:

1. Take a twig showing the brown staining and cut three sections each about as big around as your finger and 10 cm long. Do not remove the bark!  Before you use those tools on another tree, clean them with alcohol to avoid spreading the disease.
2. Wrap the samples in wax paper and put them in an envelope.
3. Send the samples immediately to the following address along with your name, address, and phone number.

Crop Protection Laboratory
346 McDonald Street
Regina, SK S4N 6P6

It is also wise to phone the provincial authorities at 1-800-567-4224. In Saskatoon, please refer to their website.

Other Common Diseases of Elms

Dutch Elm Disease is not the only disease that causes problems with our elms, and in fact similar symptoms may make detection of DED difficult.

Verticillium Wilt
This fungus normally enters the tree through the soil; however air-borne spores can cause direct infection of parts above ground. The symptoms may include curling and drying of leaves, abnormal red or yellow colour of leaves or areas between leaf veins, defoliation, wilting or die-back. Unfortunately, pruning of the infected branches will not eliminate the disease. If the tree is removed, then susceptible species, which includes maples and ashes as well as elms, should not be planted there.

Dothiorella Wilt
This is a fungus is spread by wind, rain, insects and birds. It enters the tree through wounds, and develops in the water-conducting system. Symptoms include drooping and yellowing of leaves, brown rolled up leaves, and wilt and die-back of branches. Infected branches must be pruned, and the tree may have to be removed.

Because DED and these wilts have similar symptoms, lab tests are often necessary to confirm the identity of the fungus. See previous section for how to collect a sample.

Article by Gary Bortolotti and Susan Kaminskyj.

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