Anna Larney with the City of Lethbridge explains Dutch Elm Disease and the signs to look out for as the elm tree pruning ban goes into effect April 1, 2025. (Photo: Lethbridge News Now)

By David Opinko

Elm tree pruning ban goes into effect April 1 in Lethbridge

Mar 31, 2025 | 11:53 AM

The City of Lethbridge is asking all residents to help prevent the spread of Dutch Elm Disease (DED).

A pruning ban on elm trees is set to take effect April 1, 2025, which will be in place until the end of September.

Anna Larney, urban forestry technician with the City of Lethbridge, says DED is a “really detrimental invasive disease” that has wiped out most of the elms in eastern North America but has not been a major issue in Alberta so far.

She explains that the open wounds on elm trees release a pheromone that attracts elm bark beetles, which introduce DED to the trees when they lay their eggs.

There are currently over 5,700 Dutch elm trees in Lethbridge’s public spaces and about as many on private properties, Larney says. That amounts to about 10-20 per cent of all trees in the city.

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“If you think of the area around the hospital and Gyro Park, all of those big, beautiful trees that make the canopies over the stress are elm trees. It’s those trees that we’re trying to protect from Dutch Elm Disease,” says Larney.

DED can completely kill a large elm tree in just one season. According to Larney, elm bark beetles can quickly spread to neighbouring trees and infect those too.

The best way to prevent DED is to notice the signs of it early and report it.

This website from the Government of Alberta can help you determine if any trees on your property are elms. Key symptoms of DED include:

• Leaves on one or more branches suddenly wilt, droop and curl.
• Leaves turn yellow, then brown and shrivel, but stay on the tree; this is referred to as flagging’.
• DED symptoms can also be seen under the bark of infected branches. When the bark is peeled back, healthy elm wood is cream coloured. But when a tree is diseased, dark brown or red streaks can be seen in the infected sample.
• DED advances quickly and the affected branch will die as more of the tree becomes infected. You might see dead leaves falling out of season.
• If the tree is infected later in the summer, the leaves on the infected branch or branches will droop, turn yellow and drop prematurely. Late season infections are easily confused with normal seasonal changes in leaf color.
• Two other vascular diseases which are not as serious as DED (Verticillium wilt and Dothiorella wilt) can mimic the symptoms of DED so a sample from the infected area of the tree must be sent to the Alberta Plant Health Lab to confirm if DED is present. See submitting lab samples.

Infected trees can be reported to the STOPDED Hotline at 1-877-837-3567.

Larney says, if you catch it early, you can also report DED to the City of Lethbridge by calling 311. An urban forestry technician can help to diagnose DED and remove the infected tree.

Other ways that you can reduce the spread of DED include buying local firewood, not pruning elm trees between April and October, and monitoring any changes to trees in your neighbourhood.

More details on DED can be found here.

Anna Larney shows a dead elm bark beetle to help residents spot them. (Photo: Lethbridge News Now)

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