Dutch Elm Disease

How do I prevent Dutch Elm Disease?

An Elm is easy to recognize.

An American Elm

An American Elm has a tall straight trunk. Branches start fairly high and grow upward to form a graceful, spreading arching shape like a vase or umbrella. (There are many American Elm trees growing at City Hall and Olympic Plaza in Calgary.)

The bark of and Elm is thick and rough, usually dark grey to greyish brown and made up of broad intersecting ridges. It is reddish brown below the surface.

The leaves are dark green, 3 1/2 inches long and 1 to 2 inches wide with jagged double toothed edges. The underside is rough because of raised veins.

How the Disease Kills Trees

Dutch Elm Disease (D.E.D.) is caused by a fungus called Ophiostoma ulmi (Buis). The fungus clogs the water conducting vessels of the tree (xylem), causing wilting and eventually death.

Dutch Elm Disease

Dutch Elm Disease only affects elm trees. The American and Siberian elm are the most common elms grown in Calgary. D.E.D. had not yet been found in Alberta. The smaller European elm bark beetle, Scolytus multistriatus (Marsh.) which spreads D.E.D. was collected on monitoring traps in 1994. The presence of these beetles does not necessarily mean that our elm trees have D.E.D., but they are in danger of infection.

You can help reduce the risk of this disease by knowing the signs and taking preventative measures.

How D.E.D is spread

D.E.D. is spread mainly by two species of elm bark beetles, 3.5mm in size. The smaller European elm bark beetle, Scolytus multistriatus (Marsh.), an introduced species and the Native elm bark beetle, Hylurgopinus rufipes (Eich.). These insects breed under the bark of dead and dying elm wood. If the wood has D.E.D., the emerging beetles will carry fungal spores with them when they fly to healthy branches to feed. These branches are infected be D.E.D. which spreads along the water-conducting system.

The characteristic pattern of the breeding galleries on the surface of the wood can be used to identify these two insects.

Tree Care Tips

Monitor the tree on a regular basis for the signs described in this brochure.


Water is the most important element of tree care. All trees need to be well watered from April to mid August, a rest period until the leaves drop, followed by a good soaking or two before freeze up. Thoroughly soak the area under the canopy of the tree, the dripline, to a depth of 18 to 24 inches, every 2-3 weeks; depending on the weather. The amount of water applied to keep a lawn healthy is not enough to keep the trees healthy.


Pruning should only be done during the dormant season when beetles are not active, (October to March). Maintain the natural shape of the tree. DO NOT TOP OR SHAPE! All tools used on diseased trees should be disinfected. It is recommended that ISA certified professionals be used.

Control of D.E.D

The best way to control D.E.D. is prevention. This includes keeping trees healthy, checking regularly for the signs of beetles and disease, proper pruning and correct disposal of dead elm wood. The beetles found in Calgary in 1994 may have been introduced with diseased firewood.

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