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
- Carrier: elm bark beetles that feed
on, and breed in elm bark.
- Victim: American elms, our most magnificent
- 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
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
Be aware if one of your elm trees
suddenly has wilting leaves on one of its branches.
- Flagging is a common early sign of
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?
Do not prune elm trees between April 1st and August 31st.
- 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.
Remove dead elm branches, and have them burned or buried.
- 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.
- 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!
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.
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
or yellow colour of leaves or areas between leaf veins, defoliation,
or die-back. Unfortunately, pruning of the infected branches will not
the disease. If the tree is removed, then susceptible species, which
maples and ashes as well as elms, should not be planted there.
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
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