Pest description and crop damage The balsam woolly adelgid feeds on the stems of true firs. White or grayish cottony masses, inside which are the purplish-black insects, can be found on the twigs, branches, or trunk. Heavy adelgid infestations may cover the entire trunk. The feeding insects cause the tree to form swollen, knobs areas at nodes and tips of infested branches. Adelgid infestations weaken trees, cause foliage to become sparse, and can kill trees. This is a serious pest in the forest and the landscape on balsam, grand, subalpine, Pacific silver, and Fraser firs. Balsam fir and subalpine fir are particularly susceptible.
Biology and life history The entire population consists of female insects, which are wingless. They are immobile except for a crawler stage. Eggs are laid on the bark, from which the crawlers emerge. Crawlers can be carried from tree to tree by wind. There are two to four generations per year.
Begin monitoring in late April to early May when crawlers can be seen. Spray in early spring at or near budbreak. Thorough coverage is necessary. Difficult to control with anything other than high-pressure spray equipment.
See "True fir" in:
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 74).