Emerald Ash Borers on retreat following tree treatments: Town

October 21, 2021 · 0 Comments

After nearly 20 years of chomping through ash trees throughout Ontario, the Emerald Ash Borer has shown signs of retreat within Aurora.

This is the finding of a report that will be before Council next week recommending the Town of Aurora continue its program of treating ash trees on municipal land with the chemical TreeAzin to combat the invasive species of beetle (EAB).

The Town has been exclusively using TreeAzin to treat ash trees since 2017.

As of this year, all candidate ash trees in municipal parks have received eight treatments over nine years, according to Parks Manager Sara Tienkamp.

“Based on the strategy program to date, it can be concluded the treatment has had various degrees of success and, for the most part, our current remaining ash tree inventory has survived a major infestation and spike in the EAB population,” said Ms. Tienkamp. “The number of trees expiring has stabilized and the insect population has started to decline. While there has been loss of ash within the weakest, less responsive trees, what remains are the most robust ash trees. Staff can confidently state that without EAB treatments, the Town would have suffered the loss of the entire inventory of ash trees.

“Street trees were selected for treatment primarily and park ash trees [were] added into the treatment program after the first couple of years of treatment. Data collected has shown that the trees have responded well to treatments and are actively growing with an average gain of 1.5 cm of DBH (diameter at breast height) yearly. All other ash trees within woodlots and open space areas were not treated and have now completely expired or are so heavily infested with EAB that they will soon be deceased.”

Between 2013 and 2021 1,015 of the Town’s total ash tree inventory in 2013 of 2,920 have been removed, with 250 of these removals attributed to the 2014 ice storm and other seasonal storm damage.

“On average, approximately 100 trees have been removed yearly but staff anticipate that number to slow as infestation declines and we are left with the hardiest specimens,” says Ms. Tienkamp.

Staff recommend the Town continue treating trees on a biennial basis now that the EAB population has declined, skipping treatments in 2022 and using the year ahead to focus on “corrective pruning, continuing with removals as they arise and replanting programs.”

“A few of the most affected woodlot/open space areas where losses of ash trees were particularly heavy occurred primarily in the northwest section of Aurora. Supplementary trees have been planted in some of these areas over time with the support of the LSRCA (Lake Simcoe Region Conservation Authority) and community planting initiatives. Fortunately, ash was not the dominant species in the balance of our woodlots and natural open spaces areas. Trees planted within the Town tree nurseries as part of the EAB Management Plan are actively being transplanted on open spaces and parks by staff on an ongoing basis. In addition, ash street trees removed are being replaced accordingly, helping to rebuild the loss in canopy cover.

“Higher levels of infestation and the age of infestation are directly related to the weakening of branches and the structural strength of the trunk. Pruning these trees would strengthen the branches of the ash the Town is attempting to preserve by reducing their weight and length. This would also reduce the chances of a critical failure in a storm event where a large portion of the tree or the entire tree fails, leaving it untreatable. It is important that the Town continue with ongoing maintenance of the trees as part of the EAB strategy to protect the investment made in ash tree preservation.”

By Brock Weir
Editor
Local Journalism Initiative Reporter