LDD moth aerial spraying set to begin in parts of Toronto

City of Toronto staff say the first round of aerial spraying for highly invasive LDD moths in several neighbourhoods is on track to begin the week of May 23.

The specific dates and locations aren’t finalized until 48 hours before the spraying happens and could be cancelled if weather changes, but neighbourhood-specific updates will be posted on the City’s website.

The second round of aerial spraying will happen sometime between three and 10 days after the first round. It should be wrapped up by mid-June.

The spraying involves helicopters flying 15 to 30 metres above tree canopies between 5 and 8:30 a.m.

Officials said crews will be applying Foray 48B, better known as Btk, which is a natural bacteria normally found in soil and is approved by Health Canada for use in cities. It targets specific species of young caterpillars, moths and butterflies and the protein, when ingested, stops the insects from feeding before dying off within two to five days.

The City published a map showing the roughly 800 hectares of land where spraying will occur. Based on egg masses found on trees and the potential areas affected, various parts all across Scarborough and North York (especially the wards near the Don Valley) along with High Park will be targeted.

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Since High Park has been deemed an environmentally significant area due to its biodiversity and a large number of oak trees, municipal staff said a product called Bovir will be used there. They said Bovir, a “highly selective pesticide” for LDD moths that contains a natural virus affecting those specific insects, will not affect other insects or other creatures.

In recent years, the spread of LDD moths has resulted in severe tree defoliation in many southern parts of the province.

According to data by the Ontario Ministry of Northern Development, Mines, Natural Resources and Forestry, approximately 1.7 million hectares of lands with trees and green spaces saw defoliation. In 2020 there were roughly 580,000 hectares of defoliation.

“It’s moving into areas of the city that haven’t been sprayed before, haven’t really seen this volume of LDD moth in the past,” Joel Harrison-Off, a forest health care inspector with the City of Toronto, told CityNews at the end of April.

Experts said there are areas with natural biocontrol agents (e.g. viruses, a fungus etc.) that affect the population of LDD moths, but hasn’t reached the level of control needed to contain the insects yet. Experts said the level of LDD moths typically rise and fall over a multi-year cycle.

While the caterpillars primarily strip the leaves off of deciduous trees, healthy trees with plenty of sugar storage in the roots can survive the onslaught of the insects for three to five years.