Cankerworms make lunch of Manitoba legislature's trees

The cankerworm plague in Winnipeg has hit some parts of the city harder than others including the grand old trees on the Manitoba legislative grounds and neighbouring Memorial Park.

The century-old elm trees have been stripped of their leaves and are covered with the silken webs left behind by cankerworms, also known as loopers, inchworms or measuring worms.

Caring for the trees is the responsibility of the provincial government.

"My staff are equally as discouraged about this as the general public," said legislative groundskeeper Jean Dorge.

Dorge said the trees are not banded to protect them against cankerworms; instead, the province sprays with Bacillus thuringiensis var. kurstaki (Btk), a bacteria that kills the worms while they're in the feeding stage.

"When my lawn needs tender loving care, when my shrubs need looking after and my perennials looking after, then I have a minimum amount of time left to do any of the banding, so we've opted to spray as the prime control," he said.

But Dorge said his crews were not able to spray this year because of rainy weather, so the trees became infested with cankerworms.

"We were really set back by the weather during that window of opportunity where it's time to do the spraying," he said.

Peak of worm cycle

The province spends $18,000 per year to inject the trees with a fungicide to protect them from Dutch elm disease. However, the defoliation caused by cankerworms can weaken trees, leaving the m more vulnerable to the disease.

He said he plans to apply to the province for approval to spray earlier in the year, and possibly band the trees for next year.

"Obviously I've got to look at it a little bit more closely," he said. "I'm not going to promise that I am going to band, but I'm not going to rule it out, either."

The city of Winnipeg, meanwhile, is continuing its nightly cankerworm control program on city-owned trees in parks and on boulevards. The program, which also uses Btk, focuses on selected streets in heavily foliaged areas that are at risk of significant leaf damage.

Cankerworm populations typically follow a five- to seven-year cycle, and their populations have been building over the past couple of years, according to officials with the city's insect control branch.

Based on historical data, the citybelieves this year may be the peak of the cycle.