Be on the lookout for Dutch elm disease

Owners urged to water healthy trees well from April to mid-August

Albertans are being asked to be on the lookout for Dutch elm disease.

“At present, Alberta has the largest DED-free American elm stand in the world, and it is important to protect this valuable resource,” says Janet Feddes-Calpas, executive director, Society to Prevent Dutch Elm Disease (STOPDED).

“STOPDED is asking for everyone’s assistance to save our beautiful elm trees from this deadly disease.”

DED is caused by a fungus that clogs the elm tree’s water-conducting system, causing the tree to die. The fungus is primarily spread from one elm tree to another by three species of beetles — the smaller European, the native and the banded elm bark beetle. They are attracted to weak and dying trees, which serve as breeding sites. Once the beetles have pupated and turned into adults they leave the brood gallery and fly to healthy elms to feed, thus transporting the fungus from one tree to the next.

“The smaller elm bark beetles have been found throughout the province in low numbers and now the banded elm bark beetle is found in larger numbers throughout the City of Medicine Hat and area,” says Feddes-Calpas. “For this reason we must be even more vigilant.”

Leaves on a DED-infected elm will wilt or droop, curl and become brown. This appears in mid-June to mid-July. Leaves on trees infected later in the season usually turn yellow and drop prematurely. Leaf symptoms are accompanied by brown staining under the bark. All suspicious elms must be lab tested, a service STOPDED funds. Suspected cases can be reported by calling 1-877-837-ELMS or going to

To keep elms healthy, owners are urged to water them well from April to mid-August. To allow the tree to harden off for the winter, watering should be stopped mid-August followed by a good soaking or two before freeze-up.

There is a ban on pruning elms between April 1 and Sept. 30 as beetles are most active at this time and are attracted to the scent of fresh tree cuts.

Transport and storage of elm firewood is illegal as DED and the beetles are declared pests under the Alberta Agricultural Pests Act.

“Our elms are a treasure that we cannot afford to lose,” adds Feddes-Calpas.

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