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By Shaun Penner

Dutch Elm Disease

City crews hoping to keep Dutch Elm Disease at bay as pruning season begins

Oct 1, 2020 | 1:45 PM

The pruning of elm trees around Grande Prairie is beginning Thursday to help ensure Dutch Elm Disease (DED) continues to remain at-bay amongst the elm population in the Swan City.

The fungal disease is carried by elm bark beetles, which are attracted to open wounds and fresh cut areas of elm trees. Parks Supervisor with the City of Grande Prairie Amy Needham says the disease is highly contagious and deadly to elm trees, not unlike the disease spread by the mountain pine beetle, known as blue stain fungus.

“When they (elm bark beetles) carry it to an uninfected tree, they pass the disease onto the tree, it spreads throughout the tree,” said Needham. “It chokes off the tree’s ability to take up water, and the tree dies, usually within one season.”

Though the beetles were discovered in Grande Prairie in 2017, they were found to be free of the disease. However, DED has been confirmed in two trees in Lethbridge, making some of the first known cases in Alberta. Needham notes the disease had spread throughout Eastern Canada, but very rare in Alberta.

With that, the spread of such a disease could have big consequences for the City’s tree inventory, which is why her department will be taking the window of time they have available to them to properly protect and maintain the trees.

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Due to the highly contagious nature of the disease, provincial regulations do not allow for elm trees to be pruned between April 1 and September 30 each year, when the beetle population is typically most active.

“Our City-owned tree inventory is right around 25,000 trees, and just around 15 per cent of those are elm trees. That doesn’t include all of the privately-owned elm trees, so we estimate there is about the same amount of elm trees that are privately-owned.”

Needham says a recent provincially-commissioned appraisal suggested Alberta’s elm tree population to be worth between one- and two-billion dollars. In Grande Prairie, that value sits at over $4 million.

For anyone who has an elm tree on there property, Needham says now is the time to do any pruning. She adds that if you do prune your elm tree, it is very important to get rid of any of the cut wood laying around and not keep it for firewood or any other purpose.

“Keeping the wood around does the same thing as leaving the dead wood on the tree, with its ability to attract the elm bark beetle and provide breeding sites.”

Needham says parks crews will be visible in residential areas and along major roadways while pruning, and she asks members of the public to use caution when around any work areas.