City of Toronto to conduct aerial spraying later in spring for invasive LDD moths

The City of Toronto has announced crews will be conducting caterpillar aerial spraying in an effort to curb the spread of invasive LDD moths (formerly known as gypsy moths) after a historic number of trees in Ontario were defoliated last year.

According to the municipality’s website, the spraying — which involves helicopters flying 15 to 30 metres above tree canopies before sunrise two times and three to 10 days apart — is tentatively set to occur between May 16 to June 15. It will depend on weather and environmental conditions. The most recent spraying occurred in 2020.

“Survey results show that the LDD moth population in 2022 is forecasted to be high in parts of the City. This may result in severe defoliation of trees unless treated with an aerial spray in 2022,” the website said.

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.

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.

The City of Toronto is holding a virtual information session about the aerial spraying program on Tuesday between 6:30 and 7:30 p.m. Click here to register for the meeting.

Ontario saw record tree defoliation in 2021 due to LDD moths

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.

“We’re talking about an infestation, defoliation, damage the size of a … country,” David Dutkiewicz, an entomology technician with the Invasive Species Centre based in Sault Ste. Marie, told CityNews in November.

“It’s really sort of shocking. I thought last year with under 600,000 hectares of defoliation is super high, we’ve never had that in Ontario’s history ever, and this year blew that out of the water.”

RELATED: Annual tree defoliation by gypsy moths tripled in 2021, and 2022 could be just as bad

Dutkiewicz said there are areas with natural biocontrol agents (e.g. viruses, a fungus etc.) that work to keep the population of insects, but hasn’t reached the level of control needed to contain the insects yet. Experts said the level of insects 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.

But Dutkiewicz said at the current levels the caterpillars can move on to coniferous trees like white pine and blue spruce. He said since those trees keep sugar in the needles, those can die off within a year.

He encouraged residents to scrap any egg masses (typically white or brown clusters) off trees with a knife and place those in soapy water for three days in an effort to reduce the amount of damage.