There are only a few days left to prune your elm trees in Alberta before the pruning ban comes into effect on April 1.

If you have any elm trees that need pruning, this upcoming long weekend is the ideal time to do so.

Elm trees can only be pruned in the province from October 1 to March 31, and this is because of Dutch Elm Disease (DED). 

According to the Government of Alberta, DED is a “costly and deadly disease that affects all species of elm trees in Alberta. It is caused by a fungus that clogs the elm tree’s water-conducting system, causing the tree to die.” 

The fungus is spread from one elm to another by three types of beetle species, which are: 

  • The smaller European elm bark beetle (Scolytus multistriatus) 
  • Banded elm bark beetle (Scolytus schevyrewi) 
  • Native elm bark beetle (Hylurgopinus rufipes) 

Barry Munchrath, owner of Positive Pruning and Maintenance, spoke about the importance of pruning your elm trees in this designated time frame. 

“It is important to prune elm trees between October 1 and March 31 because the tree is dormant. Even though pruning is essential and effective, it does create wounds on the tree. If you were to prune an elm tree in the middle of summer, you are leaving an open wound on the tree, which can attract the elm bark beetle,” Munchrath said. 

According to the government, Alberta has the largest DED-free stand of American elm in the world, and it is one of the last two locations in the world that are free of DED, due to diligent tracking and monitoring. 

“The fact that DED is being tracked so carefully is having a very positive effect on keeping control of the disease, which is important because trees that are affected can die within a span as short as three weeks,” Munchrath said. 

A recent case of DED was in July 2020, when the City of Lethbridge had two elm trees that tested positive for the disease, which were immediately removed, and this was considered an isolated case. 

Even though Alberta is free of DED, it can be spread very easily through firewood as well. 

“If you go camping, please do not transport firewood. Elm firewood is one of the largest spreaders of elm bark beetles that can carry DED. Beetles can hitch a ride on infected elm firewood and be carried by unsuspecting campers and homeowners. It is illegal to bring elm material into Alberta from a DED-infected province such as Saskatchewan,” it states on the Albert Government website. 

If you do have elm trees on your property, it is important to always monitor them. 

“If you believe that your tree has been infected with DED, call a professional to come take a look. Keep an eye out for various branches where all the leaves start to droop and go brown in patches throughout the tree, as this is usually the first indicator that the tree has been infected,” Munchrath said. 

Other symptoms can be spotted inside the trunk of the tree, but according to Munchrath, it's best to leave that up to the experts to determine, as stripping the bark creates an open wound. 

“There's a difference between the leaves turning brown in the fall and just having to die back in sporadic spots in the tree; that is a sign of a problem.” 

Keeping your trees as healthy as possible is the best way to prevent DED and other tree diseases. 

This includes regular pruning, maintaining soil composition, and frequent watering—even on mature trees. 

“I refer to the 3 D's: you need to look out for dead, diseased, or damaged branches when it comes to pruning. You shouldn't leave those in a tree, as it can affect overall health and invite unwanted pests.” 

“Soil composition is extremely important as well. If you have a tree that's 40 years old and the soil has never been touched, that soil has degraded over time and will need to be amended." 

Most importantly, thorough watering is essential for trees in Alberta, especially due to the previous and upcoming summer drought conditions.

“It's also important to take into consideration the changing climate and how much hotter it is getting in the summers. Make sure you’re watering your trees enough, and if you have rocks at the base of the tree, remove them as they generate more heat and stress on the tree.” 

The elm tree pruning ban will kick into effect on April 1 and will continue until September 31. 

If you suspect an elm tree is infected, you can report it to the STOPDED hotline at 1-877-837-3567. 

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