Dutch elm disease

By Larry Cornelis – Sydenham Field Naturalists

Don’t blame the Dutch though.

Larry Cornelis Photo

It’s just that Dutch biologists were the first to identify a pathogen that was killing the Elm trees in Europe.

Dutch elm disease is a fungus that was first introduced to Europe at the beginning of the 20th century and to Eastern North America in 1930.

This was eventually deadly to the majority of our native Elms (Ulmus).

Elms are well known and highly prized for their form, arching branches and it was once the most favoured of all shade trees.

Locally, we have three species of Elm, American Elm (Ulmus americana), Slippery Elm (Ulmus rubra) and Rock Elm (Ulmus thomasii).

The large leaves, arranged alternately on the twigs, have sharply toothed margins, pointed tips and asymmetrical bases.

They turn a golden yellow in the fall.

The seeds (a winged samara) are a good way to identify the species.

Rock Elm seeds are totally hairy, Slippery is just a bit in the centre and American has hairs on the wing margins. Elms are one of the first trees to bloom in the spring.

Larry Cornelis Photo

Rock Elm is rare in our area.

It is the smallest of the three species.

It has corky ridges on its twigs.

The largest known specimen is approximately 26 inches in diameter and 66 feet tall.

It’s known for being rot resistant, even in water.

Rock Elm timber was shipped to England in colonial times to build ships.

Slippery Elm (aka Red Elm) is a large tree, growing to over 100’ tall and with diameters of 5’ to 6’ although recently the largest in Ontario is 59”.

It’s our second most common Elm species.

The large leaves are very rough hairy above and when dry, can be used like a sand paper.

The form (ascending branches forming a dome) is not quite as ornamental as American Elm.

Slippery Elms can have tall branchless trunks compared to the other two species.

It was known for its medicinal properties and used by the Iroquois to build large canoes.

Larry Cornelis Photo

American Elm (aka White Elm), the lady of the forest, is our most prized ornamental species of Elm.

Many city streets were shaded by American Elms and today that is still true in Regina where Dutch Elm disease is just arriving.

City biologists are attempting to protect their Elms through proper care and inoculations.

American Elm is also a large tree growing to over 120’ tall with diameters reaching 8’ historically.

This is the species that has the arching form and vase shape elms are famous for.

The high arching branches make the Elm a favourite tree for Orioles to nest in.

There are still a few venerable large trees to be found locally.

Somehow, these individuals have survived the disease and are perhaps resistant.

I sure hope so.

They should be preserved for their scientific value in the fight against the Dutch Elm disease.

And there is hope on the horizon.

Larry Cornelis Photo

Botanists at the University of Guelph have been collecting cuttings and seed from these survivors and developing a resistant native Elm.

I have read that they are very close to offering these specially developed trees.

I really look forward to the day I can plant an Elm again.

Maybe, someday in the future, people will be able to walk and drive down streets lined with Elms again.

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