Say hello to spring, and emerging bark beetles

pine bark engraver beetle "frass"
For landowners, the sight of “frass” (sawdust and waste) from the pine engraver bark beetle is a familiar sign of spring. Photo: Brytten Steed, US Forest Service,

Temperatures are warming up, which means the pine engraver bark beetle will once again rear its ugly little head in forests and woodlots across the state. The pine engraver beetle is tiny — between 1/8 and 3/16 of an inch long — and tends to attack small pine trees or the tops of large pine trees.

The pine engraver typically infests fresh slash, wind throw, or snow-damaged trees by building “galleries” under the bark for its eggs to hatch. It takes about 40-55 days for the pine engraver to complete development from egg to adult. Each new generation of adults produced during the warm months begins fresh attacks on nearby wood. This bug prefers to munch on and lay its eggs in slash or other downed wood, but it also can go after nearby live, standing trees within its limited flight range. By late-August, the final generation of the season to emerge typically seeks out places to hibernate for the winter and the danger of infestation is reduced… until next spring, that is.

When they do occur, pine engraver outbreaks can include hundreds of trees, especially trees under stress because of drought and overcrowding. Thinning dense pine stands can help reduce the potential of a pine engraver outbreak. Thinning allows more water, sunlight, and nutrients to reach standing trees, which helps enhance their vigor and defensive capabilities, such as increased resin flow.

The pine engraver beetle is a native insect and plays in important role in the ecosystem. Landowners have a number of preventive options to manage the pine engraver bark beetle without the need to spray insecticides. These options include scheduling tree cutting to fall months, carefully managing the size and placement slash piles, and restricting tree pruning to certain times of the year. These options and others are described in the latest edition of the free e-newsletter, Forest Stewardship Notes, a co-production of DNR and the Washington State University Forestry Extension program. Read more in the latest issue of Forest Stewardship News.

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