Problem type: Insect
Name of problem: Adelgids
Plant name(s): Spruce, larch, pine
Symptoms / Characteristics:
Galls may be evident near the ends of twigs and branches and may be confused with cones. Galls of different adelgid species will differ in appearance. Branches will begin to swell and needles surrounding the branch can flatten and become scale-like and discolored. Galls produced by the Cooley spruce gall adelgid resemble a small pineapple.
Some adelgid species will not produce galls. Damage caused by excessive feeding includes stunted needles, twisting of needles, crooked branches and sparse foliage. All adelgid species are recognized by the presence of white "wool", powder or ribbons attached to their bodies. If population levels are high, the trunk or needles may appear as though they are covered in snow or mold.
Adelgids can be confused with true aphids and are closely related to certain aphid species, but belong to the Adelgidae family. The life cycle of most adelgids is complicated and some alternate from one host to another. In gall forming adelgids, the adult female lays eggs near the base of new needles. When the young hatch, feeding commences and gall formation begins. Galls form around the young where they continue to feed and grow. When galls dry out, adults emerge and eggs are laid on new branches. The adult female dies and her woolly body remains as a covering over the young.
Adelgids feed by sucking the sap from the tree. Damage is usually not severe and is generally only an aesthetic problem. Stunted growth or death of the tree may occur depending on the adelgid species and host plant.
Control / Preventions:
Generally, control is not necessary as tree health is usually not at risk. Adelgids can be controlled if the tree appearance is greatly reduced. Horticultural oils can be applied as a dormant spray or summer spray onto the foliage. Ensure thorough coverage is achieved, especially targeting the underside of branches.
Insecticides are available but must be applied before galls begin to form as the young are enclosed and protected by the gall. The insecticide Sevin can be applied to the foliage targeting the underside of branches. Applications should be made in the spring before eggs are laid or insects are still young depending on the life cycle of the species. Fall applications can be made but are not as effective.