Spruce Gall Adelgids - Cooley, Eastern and Ragged
Hosts: Cooley: Primarily white spruce, Douglas fir, and Colorado blue spruce; Eastern and ragged: spruce only
Evidence: Look for characteristic, sometimes unsightly, galls that may disfigure shoots on spruce only. Cooley spruce galls are pineapple-shaped and form on the end of new growth, particularly on lower branches of blue spruce (a). White woolly flocculence is associated with some adelgid life stages (b) and feeding may result in discoloration and distortion. Needles on Douglas fir, the alternate host, develop yellow blotches at adelgid feeding sites and may appear twisted. Eastern spruce galls are pineapple-shaped but can be found at the base of new shoots, especially in Norway and white spruce (c). These galls turn brown and open in late August (d). Ragged spruce galls are formed on the end of new growth, but are shorter and thicker than Cooley galls and chambers inside are joined. Needles may cover the gall surface, making twigs appear scraggly (e).
Life Cycle: These adelgids have complex life cycles, involving alternation of hosts (Cooley) and multiple generations. Adelgids overwinter as exposed immatures, and become reproductively active in the spring. Feeding during shoot elongation induces the development of galls, which are succulent at first but turn woody and dry in summer, opening to release adelgids.
Management: Green galls produced by these adelgids can be pruned out and destroyed in the spring. It may be desirable to rogue out particularly susceptible individual trees in a spruce planting to reduce populations. Horticultural soaps or oils can be applied to adults, eggs, or nymphs. Overwintering nymphs can be killed with dormant oils applied to twigs (Cooley) or terminals (eastern). Chemical insecticides can be applied in April before bud break or in September to early October.
Similar Species: There are several other spruce gall adelgids which may be locally important. See P-2 and refer to Rose and Lindquist.
Figure a: Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Morrisville, VT.
Figure b: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.
Figure c: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.
Figure d: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.
Figure e: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.
Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p. 81-83, 86;
Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs . 2nd edition. Cornell University Press. p. 112-115;
Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p. 15-17 and 58;
Rose, A.H. and Lindquist, O.H. Revised by Syme, P. 1994. Insects of Eastern Spruces, Fir and Hemlock . Canadian Forest Service Publication. p.42-48.