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Experts say the ugly black spots dotting maple leaves in the Windsor area shouldn't concern green thumbs or gardeners. (CBC)

Experts say the ugly black spots dotting maple leaves in the Windsor area shouldn't concern green thumbs or gardeners.

City forester Bill Roesel said his department has been inundated with calls reporting and inquiring about the spots, caused by the fungus Rhytisma acerinum which is commonly called 'tar spots'.

'It's more cosmetic than anything.' — Bill Roesel, city forester

"It's not terribly harmful to the tree," Roesel said. "It's more cosmetic than anything else."

The spots begin to appear in fall. Roesel said the region's overly wet summer and fall could be partially to blame for the number of cases this year.

Windsor is on pace to experience its wettest year in history.

"Certainly, we're seeing more of it this year," Roesel said.

Roesel said it's too late to do anything about the affected trees now. But, he said the fungus can be prevented from appearing next year.

Rake and compost the best advice

"The best way to reduce it or prevent [it] is to get rid of all the leaves in the fall," Roesel said.

Leaves can be raked by residents and then safely composted by the city.

Roesel said because the city composts such a high volume of leaves the temperature created by the rotting leaves rises so high it destroys the spores that cause the fungus. That may not be the case in a backyard compost pile, Roesel said.

"Don’t be alarmed. It's part of nature," Roesel said of the fungus. "As long as the leaves are gone before next spring, you can control (it)."