Dutch Elm Disease in Ontario

Elm Recovery Brochure

On a drive to Brockville, I began noticing a lot of dead elms. Now, I know that Dutch Elm Disease (DED) has stricken a lot of our elms in Ontario, and across Canada and the US. A lot of farmers are recently chopping them, and piling the wood. It got me curious.

DED has spread, beginning in 1940s in Ontario, with the local Elm Bark Beetles. They dig under the trees, contact the fungus, and spread the fungal spores. The spores block the ability of the trees to take up water.

I started wondering about the elms around us. What was the timing of them dying? It appeared that a lot were being cut down at the same time. Ours are propagating, producing copious seeds in spring, and dying, all over the property. We've had some very big ones taken down recently. The branches fall, frail as they dry out they bend, and in a big wind could be dangerous.

The University of Guelph has been doing a lot of work on elm disease. They began with taking cuttings of the strong trees that have survived this vascular disease. The work of the late Henry Kock (1952 – 2005) at The Arboretum at uGuelph has been amazing. He was the one who noticed some large elms still surviving, and began to undertake research.

We now know that the DED attacks every elm, but many trees have a strong enough immune system to live for 20 to 30 years, reaching about 20 to 40 cm diameter. Some may live 60 to 90 years and attain the classic elm silhouette. Scattered across Ontario, unusually large, surviving elms are as big as 500 cm or 15 feet in circumference. So isolated are they that little opportunity exists for DED tolerant trees to cross pollinate and produce the next generation.

Funnily enough, they found that there were many of these larger, virus-resistant trees scattered across the province.

Our database of reported elms now contains over 1800 records and we have visited over 600 of the most promising specimens which can be found throughout Ontario, from Windsor to Sault Ste. Marie and over to Ottawa.  

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• Henry Kock Tree Recovery Endowment  ( Elm Recovery Project)

Lots of seeds everywhere

We have a ton of elm trees, with many surviving, and many more dying.

I found some information on the obtuse government of Ontario site. It was just plain wrong. Our Ontario.ca website (which is horrible to navigate!) mistakenly says that the trees die within 1 - 3 years, but that is false.

OFAH/OMNR Invading Species Awareness Program. (2012). Dutch Elm Disease (This fact sheet may be reproduced for non-commercial purposes.)

How to Identify Symptoms of Dutch Elm Disease

• Symptoms can first be seen in June and early July.
• Leaves wilt and curl, turning yellow and brown in the summer.
• Branches begin to dieback and then result in death.
• Brown staining can be seen on the side of the tree when bark is peeled back.

What You Can Do

• Learn how to properly identify the signs and symptoms of dutch elm disease.
• Never transport elm wood or wood products with bark to new areas.
• Buy firewood locally when travelling or camping. Never bring unused wood home with you.
• If planting elm trees, buy from a local and reliable source.

I have many wee trees in my gardens!


You can see large and small dead elms in our forest.


It's so sad seeing them. Many have had wild grape vines taking over the tree, which provides food for animals, at least.