"We can expect all untreated ash in the city to die," Neumann said.

Half of the trees on Stephanie Drive are tagged with a bluish-green "I" spray painted on their trunks, indicating they have been injected with TreeAzin. This is the first year the city has injected trees with this product. So far, 554 trees have been treated.

For TreeAzin to be effective, trees must be injected while they are relatively free of the ash borer. Injections are made at the base of the trunk using pressurized devices to force the product into the tree.

The cost of the treatment is measured by the thickness of the tree. Homeowners may pay between $5 and $7 per centimetre of the tree's diameter. A typical mature ash in a backyard might cost a household around $200 per year to treat. Neumann said the city is paying less than that, this year spending just under $100,000 to treat about 23,000 centimetres of ash trees.

These treatments are not a one-time-only affair. The injections will need to be continued every few years, as long as a high population of ash borer exists in the area. The city's official plan suggests treatments will need to continue for at least 10 years.

In 2015, the city is aiming to inject about 550 trees again, Neumann said. The number of injections will be limited by the city's budget and whether or not staff is able to identify other mature trees still untouched by the ash borer. Some of the previously injected trees will need treatment again, while others will be good for another year.

If a tree is unstable and poses a safety risk, it will be cut down. The cost of taking down a large tree could be around $1,500 or more. The removal of smaller trees tends to cost less. When trees are cut down the branches and trunk are run through a chipper. When disposing of large trees, the city will rent a grinding tub.

In total, 105 trees have been cut down in response to the ash borer; 75 of them were felled this year. Most of them were removed from the green spaces behind the Clairfields West neighbourhood in Guelph's south end.

Neumann said the city aims to plant at least one new tree for every ash tree that comes down. Species like red maple, red oak, tulip trees, bur oak and silver maple will make up the city's future tree canopy.

The cost estimate of dealing with the emerald ash borer over a 10-year stretch is about $15 million, although Neumann said this could still change.

"There's never been an infestation like this before," he said. "Where the insect came from, it never caused this kind of problem, so nobody's ever studied it before."

Cities such as Guelph, at the front end of the battle against the ash borer, are turning to the oldest areas of the infestation, around Detroit and Windsor, for answers. Those municipalities are only now coming out on the other side of the infestation, 12 years after the invasive beetle first arrived.

The City of Guelph has set an ambitious goal of achieving 40 per cent canopy coverage by 2031. The most recent assessment suggests the city has around 20 per cent coverage. The bout with this invasive beetle will no doubt cause a drop in canopy cover, Neumann said.

"We're going to lose ground through (emerald ash borer). There's no possibility of us planting trees quickly enough."

Over the next few years, the city will continue to cut sample branches off trees to gauge how bad the infestation has become. But sooner or later this type of sampling will be pointless. Neumann said eventually all untreated ash trees left standing will start to show visible signs of the infestation. Staff will no longer need to go beneath the bark to see it.

cseto@guelphmercury.com