Natural, recurring outbreak affecting trees in Southeast Alaska continues

Western black-headed budworm defoliation near Thayer Lake in the Kootznoowoo Wilderness Area, Admiralty Island, July 2021. (USDA Forest Service photo by Robin Mulvey.)

Juneau, Alaska (KINY) – The Tongass National Forest said that residents and visitors have the opportunity to help scientists learn more about a familiar insect outbreak continuing in Southeast Alaska.

The western black-headed budworm is back and causing trees to turn reddish-brown.

The Forest Service said that while the impact may look dramatic, it is a natural part of the changing forest, and noted that this outbreak was first noticed in 2020.

Forest visitors can upload photos, videos, or information related to sightings of the insect or its damage to iNaturalist, which will automatically be included in the Alaska Forest Health Observations Project, a citizen science project in iNaturalist.

Caterpillars feed on the buds and new growth of spruce and hemlock creating a thin and red appearance. Large amounts of frass can be found underneath infested trees.

In the coming weeks, the western blackheaded budworm will continue to feed and the damage will become even more apparent.  While most trees survive the damage caused by the budworms –and some trees may even benefit in the long term—heavy concentrations of activity can lead to the death of some trees.

“People can really help us improve our monitoring of the forest and be our eyes on the ground,” said Elizabeth Graham, Ph.D., an entomologist for the USDA Forest Service Alaska Region. “We’ve noticed this year that the caterpillars are starting to feed on Sitka spruce so any observations people can upload are extremely helpful.”

The last time a major outbreak in the Southeast took place was from 1992 to 1995.