Western spruce budworm impacts visible in Chaffee County forests
The slightly brown tinge of a bathtub ring on Methodist Mountain has returned, providing visual evidence that the western spruce budworm population is active. Although its name implies the insect is present in spruce trees, it more commonly is found in Douglas-fir and white fir trees in Chaffee County. And the brown cast to impacted trees is the result of partially eaten needles drying out and dying.
The budworm has been present for several years around Poncha Pass, but there was little evidence north of Poncha Springs until last year, when the Colorado State Forest Service Salida District received phone calls from residents in Alpine about caterpillars rappelling out of trees.
“Since those phone calls in 2014, we’ve noticed spruce budworm damage in Douglas-fir between Poncha Pass and Cottonwood Creek,” said Kathryn Hardgrave, assistant district forester with the CSFS Salida District.
A native insect to North America, the western spruce budworm is a widely distributed tree defoliator throughout the West. It has a one-year life cycle, in which it develops from egg to adult. Adults are rusty-brown moths and appear from late June through August.
After mating, the adult female lays eggs on conifer needles, and 10 days later the larvae hatch to then hibernate for the winter in bark crevasses. In the spring, the larvae migrate from the bark to feed on existing needles. A week or so later, they enter developing tree buds.
Budworm populations usually are kept under control by a combination of natural factors, including predators, parasites, climatic conditions and insufficient food supplies. But multiple-year attacks can kill young trees and tree tops. They also make the attacked trees more susceptible to other insects. Dense mixed-conifer forests are most favorable to western spruce budworm populations, as all the tree cover protects the larvae from wind while they are rappelling to find new needles to eat.
“To make these damaging larvae more susceptible to predation, landowners can thin their forests to create space between tree crowns, remove small fir trees under large fir trees and retain tree species not affected by the budworm,” Hardgrave said.
She reminds landowners that a healthy forest is more resilient to native insects and wildfires, and that they can take steps to improve the health of their forest.
For more information, go to http://csfs.colostate.edu or call the CSFS Salida District at (719) 539-2579.