Pest description and crop damage Balsam twig aphids feed on needles and buds of firs. Three distinct forms of the balsam twig aphid occur. Aphids may be (1) small and yellow-green, (2) large and bluish-gray, or (3) have woolly white secretions which make them appear powdery. The aphids mat needles together and cause new growth to be deformed and stunted. Some needles are killed and drop from the tree, leaving rough twigs. The insects excrete a large amount of sticky honeydew which may be covered with a black growth of sooty mold. Healthy trees will tolerate moderate infestations easily.
Biology and life history Unlike other aphid species, there is one generation per year. The aphids overwinter as eggs on host trees. The eggs hatch and the nymphs molt into "stem mothers," which are large and blue-gray, and capable of giving birth to live young. These aphids are covered with a white waxy coating and feed on new flushes of growth, doing most of the damage. They mature into the final, winged form, the females of which lay the overwintering eggs in bark crevices.
Spray in spring. A second application may be needed in June. It is important to cover foliage thoroughly, including lower leaf surfaces.
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. 80).