Seeking Information about Western Cedar Borer, a Significant Pest of Western Red Cedar

Karen Ripley, DNR Forest Entomologist

Western cedar borer tunnels in red cedar branch.  Photo: M. Lloyd

Western cedar borer tunnels in red cedar branch. Photo: M. Lloyd

The Western cedar borer (Trachykele blondeli), or “red powder worm,” is a flat-headed wood boring beetle that causes a problem called “wormy cedar.” A 1928 bulletin describes, “Hundreds of the finest standing trees of the western red cedar … in the Pacific coast region of Oregon, Washington, and British Columbia have a large proportion of their timber riddled by the flattened, oval worm holes. … These holes wind through the sapwood and heartwood of the main trunk of infested trees and render the timber almost worthless for the higher grade uses such as shingles, cooperage, doors, furniture, finishing, cabinetmaking, shipbuilding and other high grade products.” (Burke).

Modern uses for cedar such as utility poles, finished lumber or export wood continue to be compromised due to this insect, even though the strength of the wood is not always significantly reduced. Using infested wood for rough-sawn fencing may be an option, depending on the amount and visibility of the degradation.

Adult cedar borers are between 11 and 17 mm long (roughly 0.5 inches), bright emerald green with a golden sheen, and have several darker spots on the wing covers. While their life cycle is fairly straight forward, the signs of infestation are very difficult to spot. During May and June, adult beetles lay their eggs on the thin-barked upper surfaces of living branches of western red cedar. When the eggs hatch, the slender, grub-like larvae chew into the branches and tunnel toward and into the tree trunk. The larvae mine horizontally and vertically along the annual growth rings, but occasionally cross the grain. The tunnels are packed with wood colored boring dust. Tunnels are usually less than 6 meters (19 feet) long, but can extend as far as 13 meters (42 feet)!

Adult western cedar borer.  Photo: S. Valley

Adult western cedar borer. Photo: S. Valley

Larvae require 2 to 3 plus years to reach maturity, then pupate inside a larger cell they have cut within the wood. Adult beetles chew out of the trees in early spring, feed on cedar foliage for several weeks, mate and lay eggs.

Infested trees appear normal and healthy, but they may have small, oblong exit holes where adult beetles have emerged. The main way to detect western cedar borer infestation is to cut off branches where they meet the trunk. If that part of the tree is infested, dust-packed larval mines may be seen in the exposed knot faces.

Although this insect is reputed to be associated with low elevation western red cedar, information about its specific occurrence is rare. There may be several closely related beetle species or subspecies present in the West, especially in drier forests where cedar gives way to cypress and juniper. Professional cedar log buyers may have key experience and local knowledge about the distribution and impacts of these cedar borers, but overall information is limited. An informal request for information resulted in a number of comments about host selection factors and distributions:

  • “We don’t see them rapidly moving. But once they are in a stand it seems they never leave.”
  • “The greatest infestations occurred where trees had been damaged by previous logging or storms. It was my conjecture that damaged or weakened trees were more susceptible.”
  • “It seems to be an increasing problem…some seem to think the recent below-average precipitation may play a role.”
  • “Eastern Washington and Idaho are essentially worm free in my experience.”
  • “Worm was not a problem on the Mt. Hood National Forest regardless of elevation, but from about Eugene south worms were very prevalent up to 3,000 feet; above 3,000 feet worms were generally not an issue in the Willamette National Forest. Worm on the lower elevation private timber lands in the Willamette Valley was common everywhere from Albany south.”
  • “In general worm has the greatest chance of occurring at low elevation.”
  • “Proximity to salt water was not always a predictor of worm. The Coos Bay area was very wormy, but from Newport north to Astoria worm was generally not a problem.”

I would like to gather as much information as possible in the hope of developing a research proposal or reporting system to better understand both historic and recent activity and infestation locations. If you have experience with “wormy cedar” on your property or through your forestry job, please contact me, Karen Ripley, karen.ripley@dnr.wa.gov, 360 902-1691. Thank you in advance for sharing your knowledge.

For more information see:

The Western Cedar Pole Borer or Powder Worm. H.E. Burke. USDA Technical Bulletin No. 48, February, 1928

Western Cedar Borer. R.W. Duncan. Forest Pest Leaflet No. 66. Pacific Forestry Centre, Canadian Forest Service. April 1995.