When the sun rises in Kelowna next Thursday, streets in the northern tip of the city will be empty. Residents have been told to avoid going outside and to keep their pets and livestock indoors. They have also been asked to put their children's toys inside and to cover their swimming pools and sandboxes.
Then, if all goes according to plan, a low-flying helicopter will hover over nearby stands of Douglas fir trees and spray them with pesticides in an attempt to control a tussock moth infestation that has the potential to create health problems and endanger up to 762,000 trees.
But despite the precautions, officials say the two compounds being used - nuclear polyhedrosis virus (NPV) and bacillus thuringensis var. kurstaki (Bt-K) - are safe.
"The actual spray itself is very safe," said Paul Hasselback, a medical health officer with the Interior Health Authority, which had to approve the spray program before it could get a permit from the province. "It's more a bacterial control or a biological control than a chemical control."
He added that similar spray programs have been safely used in other cities, including Vancouver.
The spray can irritate some people's skin and eyes. Besides the recommendations to residents, spray areas have been selected so that water intakes in nearby Okanagan Lake will not be affected, and parks where the pesticides are being applied will be closed for 24 hours. The operation is also being conducted first thing in the morning when winds are low in an attempt to minimize drift.
"It's being very precautionary but not unreasonable," Dr. Hasselback said. He added that as with all spraying programs, "it's best to avoid any exposure.
Tussock moths are native to the B.C. Interior, and outbreaks occur every 10 to 15 years. The moths strip fir trees of their needles, leaving them with a scorched look. Defoliated trees are more susceptible to other insects and often die.
Douglas firs account for 33 per cent of Kelowna's tree population.
In addition, about 20 per cent of people and animals are allergic to the moths. While most who are exposed will suffer only watery eyes or rashes, in extreme cases, reactions can be life-threatening.
The last tussock moth outbreak in Kelowna was in 1998, said Blair Stewart, the City of Kelowna's urban forest health technician. Then, like now, the problem was dealt with through spraying.
In January, 2009, the city restricted the use of pesticides by homeowners for health and safety reasons. Mr. Blair said there are no contradictions between the goals of the bylaw and the city's plan to control tussock moths.
"These are not cosmetic pesticides. We're actually using them to improve the [tree]canopy, to improve public health," he said. "If we don't do anything, then the public will use our parks and will end up having either respiratory issues or just allergic reactions to the tussock moth itself. It's something we had to step in because there's too many things involved."
As part of its permit process, the city had to get consent from residents who live in the spray zones or in areas that officials have calculated could be subject to drift. Other residents are being informed through local media.
Not everyone is comforted. Clint Best lives just over 300 metres away from one of the spray zones in Knox Mountain Park, and has an eight-year-old daughter. His family was not contacted directly by the city.
"I'm not even sure what that particular moth is all about," he said. "If something's going to be dropped out of the sky near my home, it would be good to know about it and I wouldn't just count on the fact that somebody's read that in the paper."
About 250 hectares will be sprayed within the City of Kelowna, along with another 1,060 hectares in the neighbouring regional district.
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