The Ministry of Forests is in the early stages of planning an aerial spray program next year to control spruce budworm infestation centred near the Coquihalla Highway.

The region between Kamloops and the Nicola Valley, including Logan Lake to the west, is the site of the worst infestation in the Southern Interior, entomologist Lorraine Maclauchlan said Thursday.

Following egg mass counts and aerial surveys earlier this year, Maclauchlan is now laying out areas for possible spraying with Btk, a naturally occurring organic product, in June next year.

The ministry estimates 275,000 hectares is infested with spruce budworm, which threatens supply of fir.

“It starts as you’re heading over the Coquihalla at Inks Lake and toward Logan Lake and Merritt,” Maclauchlan said. “You can see the browning.”

Spruce budworm is a naturally occurring insect that defoliates trees, largely feeding as larvae on buds growing in spring. It rarely kills mature trees, but can stunt growth for as long as a decade and kill juvenile trees in the canopy below.

The outbreak is of particular concern because B.C.’s pine forests are decimated by mountain pine beetle, increasing reliance for decades to come on healthy fir and spruce.

The ministry has conducted spray programs continuously for years, focusing on outbreaks in the Southern Interior.

“We’ve really decreased the population,” Maclauchlan said. “Btk works. (But) this past summer, densities were so out of the norm.”

Btk is a bacteria ingested by larvae, killing them. It occurs naturally in the soil and does not harm mature insects.

Last year the ministry sprayed about 55,000 hectares of forest. Maclauchlan said the ministry is looking at about the same number next year.