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Tree Pest Caterpillar Control Program underway

Program aimed at reducing defoliation and supporting tree health

June 11, 2020

With recent dry and warm weather, tree pest caterpillars are beginning to feed on leaves in areas of the city with a high density of elm trees. To combat this infestation, the City’s Insect Control Branch crews are working to protect the affected tree canopy.

“The Tree Pest Caterpillar Control Program typically starts in mid-May and works to reduce populations of spring and fall cankerworms and other species of pest caterpillars,” said Ken Nawolsky, Superintendent of Insect Control.

Nawolsky said the City uses a biological insecticide approved by the Pest Management Regulatory Agency which won’t harm other living things like birds and other insects, and operations will continue in affected areas for about a month.

“Weather permitting, crews work day and night and use slow moving trailer mounted high pressure sprayers to target areas with the potential for significant defoliation,” he said. “Residents are asked to please park their vehicles in an off-street parking location when their street is scheduled for treatment.”

This season’s program will be treating City boulevards and focusing on City parks and cemeteries where tree pest caterpillar species are defoliating trees. 

If left unchecked, a large population of tree pest caterpillars can completely defoliate a tree, and infested trees are distinguished by the appearance of holes in the leaves. The trees will survive, but it will take about three weeks for them to re-leaf.  


Animals and Insects Homeowner, Renter and Business Information Parks, Trees and the Environment