City to spray for moths in North Cheyenne Cañon area

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A western spruce budworm larvae. - J. ADRIAN STANLEY
  • J. Adrian Stanley
  • A western spruce budworm larvae.

On the morning of May 24, City Forester Dennis Will drove through North Cheyenne Cañon Park, stopping to collect small branches from Douglas fir and white fir trees at various elevations.

Later in the day, when he was showing the branches to reporters, a tiny millipede-like creature broke free from its silken tent, called a “hibernaculum,” and crawled along a branch.

It was the larva of a western spruce budworm, a type of moth endemic to the area. The little larvae feed on the new growth on Douglas fir and white fir, which make up 60 percent of the forest in relatively shady, wet North Cheyenne Cañon, and while Will says they haven’t reached epidemic levels, they’re edging close. A survey of host trees in the area found 78 percent had budworms.

That’s a problem, because those larvae will feast on the trees, leaving them weak and vulnerable to bark beetles, which can go on to kill them. From 2014-16, moths defoliated 100 percent of certain patches of the area’s forest, Will says, leaving the trees brown. Dead trees threaten water quality from the watershed, which provides about 15 percent of the city’s water, and put the area at higher risk for wildfires.

Last year in June, the city sprayed the area with bacteria commonly found in soil, foliage, wildlife, water and air. Bacillus thuringiensis subspecies kurstaki (Btk) kills moths and butterflies if they feed on impacted plants while in their larval stage. The city had hoped to wipe out most of the budworm larvae, along with another species that had reached epidemic levels and does similar damage, the tussock moth. Will says the spraying — which also took place on nearby private lands whose owners covered their share of the cost — was very successful in killing off tussock moths. But tussocks and budworms reach their larval stage at slightly different times, and the budworms survived.

“Our process is about three weeks earlier now than it was last year,” Will says.

Now, the city is planning to spray again, using the same bacteria, beginning around June 5. Will says the weather conditions have to be right, so it’s impossible to say the exact day spraying will begin. But there’s a brief window in which the spray will be most effective, since larvae emerge from hibernation in their hibernacula earlier at lower elevations and feed for about 30 days before reaching maturity. To have the maximum impact, Will wants to make sure that the larvae at higher elevations have come out to feed, and that the lower-elevation larvae are still feeding.

The city plans to close affected parks while spraying from a contracted helicopter. The spray will cover about 812 acres of city land in North Cheyenne Cañon and Blodgett Open Space, as well as 1,344 acres of land owned by The Broadmoor, 275 acres of the Cheyenne Mountain Zoo and other stretches of private and county land. All entities will pay their own costs, at $79.50 per acre. The city cost is about $67,000.

Will says that last year, residents had concerns about the spraying, but the city did not receive any complaints following the treatment. Eric Howell, forest program manager for Colorado Springs Utilities, says that during spraying, Utilities diverts area water from the drinking supply, then tests it before allowing it to feed back into the system. The spraying caused no problems, he says.

This year, Will notes that the city has sent notices to nearby residents, who can also opt to sign up to receive updates at coloradosprings.gov/budworm. Pesticide-sensitive residents can also register with the Colorado Department of Agriculture to be notified prior to treatment. A meeting to take public comments will be held at 6 p.m. on May 31 at the Ivywild School, 1604 S. Cascade Ave.

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