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Photo by Larry Wong / POSTMEDIA NETWORK

The insects, which look like dark disks with white rims on branches, hatch hundreds of minute larvae each spring that crawl or blow on the wind to nearby elms, creating withered limbs along a boulevard.

They excrete a sugary waste called honeydew that can cover trees, leading to the growth of mould that turns bark black, and create a gummy mess on cars, patios and sidewalks.

“If you stand under the tree, you can actually feel the honeydew dripping down,” said Jenkins, pointing to an elm gleaming with the liquid among many infested specimens on the west side of the Commonwealth Community Recreation Centre.

“I was walking down Whyte Avenue recently and I thought ‘Is it starting to rain?’ ”

Scale is hurting trees across Alberta and in the United States.

Lethbridge residents became so upset about the problem, which started a decade ago with tainted trees planted in a subdivision, that the city spent $610,000 last spring injecting almost 3,800 elms with insecticide.

It also chopped down 65 trees that couldn’t be saved.

Jenkins is watching the results to see if the treatment would help in Edmonton, and the city has also sprayed horticultural oil to try smothering the insects.

Homeowners can try power washing scale off smaller elms, and should ensure the trees have proper amounts of water and fertilizer to keep them strong.

Many of the worst specimens are in poor growing locations such as parking lots and around shopping centres, where they don’t have much soil, he said.

But Edmonton’s 80,000 public and private elms are considered the world’s largest population free of Dutch elm disease, and they need protection, he said.

“(They) give a fantastic, cathedral-like canopy over the city.”

gkent@postmedia.com

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