Starting late this week and until the end of the month, a contractor hired by the city will be injecting ash trees to prevent emerald ash borer infestations.
The emerald ash borer, a non-native, destructive beetle that affects all species of ash trees, was first found in Guelph in 2011. Today, there are only around 1,400 ash trees left in the city, and only 140 are healthy enough to receive the treatment.
The treatment is an injection of an insecticide called TreeAzin, which is naturally produced from Neem tree seed extracts. This year's treatment program will cost $30,000 in total.
“That’ll be done before the end of August, and we’ll continue to treat them every other year as long as they remain healthy,” said Timea Filer, urban forestry field technologist for the city.
Symptoms that appear when a tree becomes heavily infested include loss of leaves and dead branches, yellowing leaves, adult beetles feeding on leaves, high woodpecker activity, vertical cracks in the trunk, and small D-shaped holes.
Left untreated, the tree will eventually die, and can become a safety hazard.
There are currently around 1,260 ash trees left on city property, in streets or parks, that the city is planning to remove, Filer said, with additional trees in natural areas like trails.
Trees only need to be removed once they die or become a danger to the public, which city staff monitor year-round.
“Some of those are still in good condition, but we're not treating those. So only 140 of the ash trees are still good enough for treatments. And even some of those may not survive,” she said.
For example, two years ago they injected 190 trees, and have since lost 50 of them.
“Some are still doing quite well, and, and the treatments are still effective for them,” she said. But for the others, the treatment wasn’t as effective, or they started treating it too late into the infestation, she said.
To make matters worse, severe drought over the last five years or so has caused the trees to be “extremely stressed,” which reduces how effective the treatments are as well.
While the emerald ash borer population is past its peak in Guelph, she said it’s still a possibility the population could wipe out all the ash trees here.
“But you know, every once in a while we come across an ash tree that for no known reason, is doing just fine and hasn't been affected,” Filer said, adding that there is interest in researching the more resilient ash trees.
In the same vein, the city has also planted some blue ash trees in natural areas as an experiment, since they tend to be more resilient.
“In the future, what I'm hoping for is that we'll find a population of ash that are resilient to the emerald ash borer, because it's not likely that the emerald ash borer will completely disappear,” she said.
Tree removals are scheduled to take place in several parks around Guelph starting this fall until spring 2024. You can see the full list of parks here.
