Washington DNR Reports Outbreak of Western Spruce Budworm

A few weeks ago, the Washington State Department of Natural Resources released its annual Forest Health Highlights report following flyovers of more than 20 million acres of forested land across the state.

Surveyors mapped approximately 545,000 acres with some level of tree mortality, tree defoliation, or foliar disease in 2024.  That was a nearly 30,000 acre increase from 2023 and more than the 10-year average of 519,000 acres, but well below the 672,000 acres mapped in 2022.

“The Forest Health Highlights DNR publishes each year makes the long list of things impacting our forests accessible and understandable to everyone from land managers to casual recreators,” said Commissioner of Public Lands Dave Upthegrove. “The report illustrates the importance continuing to increase the pace and scale of not just forest health treatments but monitoring of forest health conditions.”

Silver Fir Beetle Numbers Up Last Year

Outbreaks of silver fir beetle in Washington are rare, but spikes in population sometimes occur following windthrow events that generate abundant breeding material.  Scientists mapped approximately 2,900 acres of SFB-caused mortality in 2024, the largest acreage documented since 6,400 acres were affected in 2004.  Recorded mortality by SFB cratered in 2005 and remained low until 2015, reaching a peak of 1,700 acres in 2023 before falling again prior to 2024. It is possible that windthrow caused by 2024 weather events such as the bomb cyclone in November created additional SFB breeding material.

Areas with recorded SFB mortality in 2024 included North Cascades National Park in Whatcom County, the Snoqualmie Pass area in King County, and the Alpine Lakes Wilderness along the border between Chelan and Kittitas counties.

“Silver fir beetle may not be responsible for the largest or most damaging impacts we see on an annual basis, but they can be some of the most visible, given where they can occur,” said DNR entomologist Glenn Kohler. “We will certainly be interested to see if the current peak is sustained for a second year.”

After Several Quiet Year, WSB Returns To Washington Forests

Western Spruce Budworm defoliation in Washington surged to more than 63,500 acres mapped in 2024 following three years of no recorded defoliation attributed to WSB. Outbreaks of this native insect are not uncommon in Washington, and this outbreak remains much smaller than an outbreak in 2011 and 2012 that affected more than 500,000 acres.

The current outbreak is most visible east of Ross Lake in Whatcom County, Skagit County, and Okanogan County.

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