Trees will be sprayed to prevent leaf loss
Five in Dundas Driving Park, one in Fisher’s Mill Park infested by ‘spongy’ moth egg masses
Targeted organic biological insecticide spraying of six Dundas cityowned trees, including the heritage chinquapin oak in Fisher’s Mill Park and five trees in Dundas Driving Park, will try to prevent further damage from “spongy” moth caterpillars.
A Feb. 13 City of Hamilton information report to public works committee stated surveys following two aerial sprayings last year found the moth population was declining — but discovered “persistent pockets of infestation” in six Dundas trees — as well as other Ancaster and Hamilton locations — “that may experience severe to moderate defoliation in 2023.”
That sparked a localized treatment program this year, featuring ground spray treatment, along with manual egg-mass scraping and tree banding. Aerial spraying is not planned, due to isolated infestations.
In addition to the chinquapin oak, named an Ontario Heritage Tree by Forests Ontario in 2012, two bur oaks, two white oaks and one red oak in the Driving Park will be treated.
City spokesperson Emily Trotta said trees with a large number of egg masses have greater potential of defoliation when caterpillars emerge.
“Defoliation puts stress on trees and makes them more susceptible to disease pressure,” Trotta said.
Trotta said on Feb. 14 that spraying was not yet scheduled, but staff aimed to complete it between midMay and mid-June.
“Residents will be advised of the application at least a week in advance of work beginning,” Trotta said.
Coun. Alex Wilson, Dundas’ representative, noted spraying can be controversial and residents will want to know when it’s happening.
Wilson asked director of forestry Robyn Pollard about potential impacts of the organic insecticide on other species — such as butterflies and their caterpillars — that should be protected.
Pollard said targeted spraying will limit impacts on other species and said there are no issues for humans.
She said a “buffer area” will be set around trees to be sprayed and residents within the area will be notified.
Pollard said more information on the pest, insecticide and spraying updates will be available on the city’s website (Hamilton.ca/ lddmoth).
Dundas resident and ecologist Steve Hill organized the augmented reality tour of historic big trees in Dundas Driving Park last year. The amount of interest showed him the connection people have to trees.
Hill said the more than 300-yearold burr oak next to a baseball diamond was almost entirely defoliated by spongy moth caterpillars a couple of years ago.
He pointed out several small, white egg masses on the bur oak, and several other oak trees in the park targeted for treatment. Hill said each tiny sack could include between 900 to 3,000 eggs that can turn into voracious caterpillars.
“It doesn’t take much,” Hill said. “It’s amazing the amount of damage these caterpillars can do. If you get that defoliation several years in a row, it can be really damaging.”
He said after caterpillars form, they migrate down the tree and go into ground around the tree during the day for protection, so spraying the ground around the tree during the day might be key to eliminating them.
There were also egg masses on the kitchenette roof next to an infested red oak.
Hill suggested a really cold winter might help kill egg masses, and wondered if there’s concern due to this season’s unseasonably warm temperatures.
He was happy to see various generations participating in the park’s big tree tour last year.
“I think it’s ingrained in a lot of people. There’s something appealing about trees,” Hill said. “I’m optimistic that people are interested, especially in old trees.”
He said projects like the tree tour encourage people to plant native species, learn more, and hear a message of hope in the midst of a climate crisis and biodiversity crisis.
“It’s a bit overwhelming,” Hill said. “There are things you can do, and it can scale up to have a positive impact.”
It’s amazing the amount of damage these caterpillars can do. If you get that defoliation several years in a row, it can be really damaging.
STEVE HILL DUNDAS RESIDENT AND ECOLOGIST