Insect Pests of a Spruce

Bark Beetles

Multiple species of bark beetle can be pests of spruce, including engravers and red turpentine beetles. These small, cylindrical insects feed on the inner bark of spruce, leaving winding tunnels under the bark. Red turpentine beetles tend to attack the lower portion of the trunk where they leave large white to pinkish-brown pitch tubes. Engraver beetles (Ips spp.) attack near the tops of the tree. Although bark beetles rarely kill trees, they can contribute to decline and little can be done to treat a bark beetle infestation. Proper cultural practices and species selection are the best means to prevent or treat a bark beetle problem.

Gall-forming adelgids such as the Cooley and eastern spruce gall adelgids cause the development of pine cone or pineapple-shaped galls, or growths, on the new growth of a spruce tree. Adelgids are small, dark insects that produce cottony white tufts on trees. A high adelgid population feeding on a spruce can cause yellowing, needle drop and dieback, although vigorous plants can tolerate a degree of feeding. Control this pest by pruning off and destroying galls when they are still green. Avoid applying excessive fertilizer, spray the cottony masses with a forceful stream of water or apply a narrow-range oil in the spring.

Sawflies are dark, asplike insects that feed on needles, buds or shoots as adults or larvae, causing tip dieback and some needle loss. Trees can tolerate some amount of feeding. Prune damaged portions of trees, avoid using broad-spectrum insecticides that harm natural sawfly predators and, if necessary, apply an insecticidal soap or narrow-range oil to kill larvae.

Foliage-feeding caterpillars and needle miners including webworms, spruce budworms and various moth larvae are occasional spruce pests. A severe caterpillar infestation can cause needle loss and branch dieback. Clip off and destroy infested branches and provide trees with proper fertilization and watering. Control larvae, when young, using applications of Bacillus thuringiensis.

A handful of additional insect pests may occasionally be bothersome on a spruce tree or shrub. These include aphids such as the giant conifer and spruce aphids, species of armored scales, mealybugs, the white pine weevil, pinewood nematodes and spittlebugs.