Dutch Elm Disease / Elm Bark Beetles
Dutch Elm Disease / Elm Bark Beetles
In September, the Saskatoon Parks Department confirmed they had found Dutch Elm Disease (DED) in six elm trees – three in Varsity View, one in North Park, and two in Westmount. The Director of Parks, Thai Hoang, announced that as part of their response plan, they would be immediately removing a total of eight trees. Elm firewood was also removed from private properties in the area.
Dutch Elm Disease was introduced to North America in the 1930’s from Europe and the U.K. Millions of elms were killed in the UK, while France lost 97% of its elm population. The disease and beetle vectors travelled to North America via imported wood products, first to the upper eastern U.S., reaching Eastern Canada during the second world war. They travelled west following the elm stands in river valleys, through to Saskatchewan in 1981. By 1989, over 70 million elms in North America had been lost. This was an astonishing 75% of North America’s elms.
In 2020 DED was detected on trees in Lethbridge Alberta and this summer it was found on four trees in Edmonton. It was also detected in June 2024 in the Kootenay Boundry Regional District of B.C.
Winnipeg has been hit especially hard in the past few years and continues trying to play catch-up to remove over 8000 American Elm trees tagged for removal.
Dutch Elm Disease is an extremely serious fungal disease spread by three species of Elm Bark Beetles.
In Saskatchewan, two of those species are primarily responsible for spreading this disease to Saskatoon’s American Elms in particular and Siberian Elms as well. They are the Native Elm Bark Beetle and the European Elm Bark Beetle. Adult Elm Bark Beetles are attracted to fresh pruning cuts and can fly up to two kilometers in search of elm trees to feed on.
The Native Elm Bark Beetle is attracted to larger branches while the European likes to feed in the crotches of 2-3 year old twigs. They carry the sticky fungal spores on their bodies from infected elms to healthy elms. Elm firewood and pruned branches can carry the disease as well. DED is also spread through tree root grafts and by infected pruning tools. The fungus can grow on stressed and dead wood and also produces airborne spores. Elm firewood may contain overwintering larvae or adult beetles that carry disease spores.
Elm bark beetles and their white legless larvae feed on the cambium layer of the tree, creating shallow tunnels under the bark, where the adults mate and lay their eggs. These feeding galleries (tunnels) and the disease block the trees vascular system, eventually resulting in tree death. This can take from one to three years.
Symptoms of Dutch Elm Disease
There are thousands of American Elms in Saskatoon. Their umbrella shaped canopies line the streets of our older neighborhoods. They are beautiful, large elms that can live up to 250 years. American Elms have no resistance to DED. The Siberian Elm is not as susceptible but can still carry the disease. Early detection of this disease is so important.
First determine if you have elm trees on your property or on the boulevards outside your home. There are many websites regarding elm tree identification you can study.
The symptoms of DED on elm trees usually begin to show around mid-June lasting into mid to late July. An upper branch or branches of the elm will begin to droop (flag), the leaves will turn yellow, curl, eventually turn brown and continue to hang on the tree. Over the summer, more branches will die back. Dead leaves will fall off the tree by the end of summer. In all cases, the affected branches are stained reddish brown or bluish brown under the bark.
What Can I Do?
Be proactive, keep your elms healthy by being vigilant. Water, fertilize and check routinely for any signs of elm bark beetles or DED.
The adult beetles are tiny but do learn to identify them if possible. There are many pictures on the internet. Learn to identify their feeding galleries.
Be observant. Take a look at the elm trees as you take your daily walk. Are the upper branches green or do you notice a yellowing and drooping of the branch ends?
Respect and abide by the Elm pruning ban from April 1 to August 31 of each year.
Do not transport, store or burn elm firewood.
Do not build treehouses in your elm in the back yard. Even the open nail and screw holes can attract elm bark beetles.
When the pruning season is open (September 1 – March 31) sterilize all pruning tools. Wash your hands routinely as you prune. Do not store any of the pruned branches on your property or put them in your green bin. Take them immediately to the City Landfill where you can dispose of them free of charge.
If you suspect your elm(s) have DED immediately phone the city to perform a free DED check of your trees.
In Manitoba, Saskatchewan, and Alberta it is illegal to use, store, sell, burn or transport elm firewood. If you are unsure what type of firewood you have call the City of Saskatoon Parks Department or Urban Forestry at 306 -975- 2890
DED resistant elm research continues in North America, Europe and the U.K. While no elm cultivar is totally immune, the creation of hybrids using disease resistant elms looks promising.
The City of Saskatoon Parks Department works diligently on testing, identification and has had a response plan in place for quite a few years. Please go to the City of Saskatoon and the University of Saskatchewan, Saskatoon websites where there is a wealth of information regarding this deadly disease.
Talk to your neighbors about this threat to our elm trees. Get the word out. We can all do our part to save these beautiful trees.