Douglas, Elbert counties

Sawfly outbreak affecting pine popualtion

Officials seeing record number of sawfly larvae in Elbert County and southern Douglas

Courtesy photo
Pine sawfly larvae outbreaks have been found in Elbert and southern Douglas County. Sawflys can defoliate pine trees and potentially kill them.
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A little larvae is causing some major damage to trees in Elbert County and southern Douglas County.

Epidemic levels of the Pine sawfly, a native insect that defoliates ponderosa pines, have reached areas south of Denver, according to the Colorado State Forest Service.

The outbreak is believed to have started near the border of El Paso and Elbert counties, and has now been detected on the southeastern fringes of Douglas County.

“We've heard some people say that if you see them, then five days later the trees will be dead. That's not true,” said Meg Halford, Assistant District Forester for the Colorado State Forest Service's Franktown District.

“If you see a tree that has been exposed and it still has some of those green needles on it, chances are that come spring it will be fine. It might experience a little defoliation, but it's probably going to make it.”

Residents in the area can expect to see heavy defoliation of pine trees and large numbers of visible sawfly larvae in the trees themselves and on the ground beneath them.

The Colorado State Forest Service and USDA Forest Service are monitoring the outbreak and believe many of the larvae are depleting their food source and dropping to the ground early, before they mature, and are expected to die before they become adults. Mature larvae, which hatch in spring and feed on living needles until late summer, soon will drop from trees to pupate in the upper soil layer of the forest floor.

“By now most of the larvae have entered the pupate stage and won't be causing much more of a problem until they hatch in the spring,” Halford said.

According to officials, sawfly activity has been common and cyclic in the area for years. However, this outbreak is more severe, possibly due to an unusually large number of eggs deposited on pine needles by adult sawflies last fall.

What environmental factors may have accelerated this spike in the sawfly population is unknown.

“This is perhaps the largest outbreak seen in this area,” said Bill Ciesla, an entomologist with Forest Health Management International, who has worked closely with the CSFS to monitor the outbreak.

Natural population controls, including virus diseases, parasitic wasps and other predators can combat sawflies.

Chemical insecticides are effective in spring when the eggs begin to hatch. However, the most effective time for direct control this year has passed.

The only areas where chemicals may be effective now are where trees are showing only partial defoliation and the risk of larvae developing into adults is high.

Halford said that measures will be taken to monitor sawfly egg deposits this fall to determine the potential for additional damage in 2015. In the spring, the CSFS will survey the threat and begin spraying the needed insecticides in affected areas.

“I know it can be hard for people, but our advice right now is to sit tight until spring,” Halford said. “There's no way for us to know exactly when the larva will hatch, but we expect May or June.”