Hot, dry weather accelerated Toronto's emerald ash borer tree crisis

toronto.ctvnews.ca
Aug. 25, 2016
By Chris Herhalt

City crews are fighting to save some of the last ash trees left in Toronto from a nasty little beetle that is poised to wipe out the species in the city by the end of this decade.

In 2001, Toronto could boast it had 860,000 ash trees throughout the city. It now has about 9,500 thanks to the emerald ash borer and that number is dwindling fast.

The emerald ash borer is a tiny beetle that originated in China and parts of East Asia. It was first detected in North America in the cities of Windsor, Ont. and Detroit, Michigan in 2002.

The beetle bores into the bark of a host ash tree and eventually hollows out and kills a tree over a period of one to four years.

The hot and dry weather the city has experienced this summer has made the situation worse, according to Kristjan Vitols, a supervisor with the City of Toronto’s forest health care unit.

“The kind of extreme heat that we’ve had is not going to negatively affect them, it may even help it get through its larval stages even faster.”

The emerald ash borer and the rapid destruction of ash trees has had significant consequences on the environment.

Vitols says city studies completed a decade ago, before the borer appeared in the city in 2007, indicated as much as 8.5 per cent of the city’s total tree canopy was made up of ash trees. Natural Resources Canada says it has been detected as far north as the northern suburbs of Montreal and Manitoulin Island.

Tree canopies help keep neighbourhoods cool during extreme heat, resulting in less energy and water consumption as well as soil erosion.

The city had a proven method to fight the bug but the drought this summer has impeded the process.

When crews find a tree infected by the emerald ash borer on public land, they inject it with Tree Azin, an insecticide that has been proven to stem the tide of an ash borer infestation in a tree over a period of a few years. Unfortunately, the dry and hot weather has significantly weakened the insecticide’s potency.

Nonetheless, the city still plans to inject close to all remaining Ash trees on public property with Tree Azin this year. However, the cost of the treatment has proven to be another obstacle in the treatment’s success.  The treatment can cost as much as several hundred dollars per tree every two years, and private property owners must pay for their own trees’ treatment out of pocket, City of Toronto forestry supervisor Jozef Ric told CTV Toronto.

Even the winter season won’t provide any relief. The Emerald Ash Borer can survive in temperatures of up to -30 C.

Vitols says it is only a matter of time before the Emerald Ash Borer kills most if not all of the untreated ash trees in the city.

“It’s essentially a losing battle,” he said. “It will essentially kill every ash tree that it comes across in southern Ontario.”

He expects most untreated ash trees in the city to be dead or dying by 2019 or 2020

“We are going to lose all of our ash (trees) in the city. And depending on what private property owners are doing they will lose their ash (trees) as well.”