Winnipeg to spray for spanworms in addition to cankerworms this spring

By | June 8, 2020

Winnipeg plans to spray for a second tree-borne worm species this week — but the city isn’t facing another “wormageddon.”

The city’s insect control branch plans to spray downtown’s Broadway-Assiniboine neighbourhood, West Broadway and parts of Wolseley in the coming days for elm spanworms, the dark-purple inchworms capable of defoliating the urban forest in areas along rivers.

Insect control spokesperson Ken Allen says if weather permits, the city will spray for spanworms this week using the biological agent BTK, whose active ingredient is the bacterium Bacillus thuringiensis kurstaki. Worms that ingest BTK lose their stomach lining and die.

The city has been spraying for cankerworms, the green inchworms that are widely dispersed throughout Winnipeg, since May 25. Several neighbourhoods in North Kildonan, West Kildonan, the North End, Elmwood, East Kildonan, St. Boniface and Fort Garry have already been treated with BTK.

Other neighbourhoods in East Kildonan and parts of Tuxedo will be sprayed tonight.

Allen described the spanworm and cankerworm infestations this spring as average. Forest-tent caterpillars are not active this spring, he said.

In 2017, all three species were defoliating Winnipeg trees in what was dubbed “wormageddon.”

Allen said the Insect Control Branch is also applying larvicides to standing water to prevent an early emergence of adult nuisance mosquitoes.

The city uses two agents to kill mosquito larvae: methoprene, a chemical that prevents mosquitoes from maturing; and BTI, the bacterium Bacillus thuringiensis israelensis.

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