Balsam woolly adelgid

Inspect branches and main stems of silver fir and other true firs closely for small cottony white masses clustered on bark; these are colonies of adelgids covered in white waxy material. Heavy infestations can stunt branch growth or cause branch dieback. Swollen knots may form where adelgids feed on young growth.

Maintain tree vigor through adequate moisture and wind protection; healthy trees tolerate adelgid feeding better. Prune heavily infested twigs in winter when pests dormant. Horticultural oil applied in March coats overwintering stages and reduces spring populations. Apply insecticidal soap when crawlers are active in spring or early summer. This pest causes more damage in coastal areas.

First detected in the Pacific Northwest in 1930 in the Willamette Valley. Caused extensive mortality of subalpine, grand, and Pacific silver firs throughout Washington and Oregon during the 1950s and 1960s. Ongoing impact in western Washington forests, particularly removing grand fir from low-elevation areas of the Puget Sound trough, Willamette Valley, and coastal streams. Land area affected in the PNW increased from 83,325 acres (2004) to 108,128 acres (2005). More damaging in coastal areas where higher humidity favors population development. Subalpine fir is the most susceptible PNW species; Pacific silver fir is the second most susceptible. Extensive mortality of subalpine fir documented in Washington and Oregon mountain environments since the 1950s. Source: USDA Forest Service; Wikipedia