On Norway spruce trees and occasionally white, black and red spruce, small, greenish growths appear where small side branches meet the stem. The galls turn brown as the summer progresses and are more noticeable by fall. The galls are generally not life threatening to the trees, however, in large numbers, they can become quite unsightly.

Growth will continue past the galls but the branch may become stunted. When large numbers of galls are present, the stems may become weaker and more prone to dropping off in wind storms.

 Problem:

 These growths are caused by an insect called the Eastern spruce gall aphid. The insect spends the winter at the base of a terminal bud. When buds begin to grow in the spring, the aphids lay clusters of several hundred eggs that are covered with white, waxy threads. The young that hatch from these eggs feed on developing needles. They suck the juices from the needles, inducing the formation of galls that then enclose them. The aphids live and feed in chambers inside the galls. In mid to late summer, the galls turn brown and crack open. Aphids that emerge lay eggs near the tip of the needles. The young that hatch from these eggs spend the winter at the base of the buds.

A similar problem on Colorado blue spruce trees is caused by the Cooley spruce gall. These growths, however, are formed at the tips of the branches. The Eastern spruce galls form near where a twig joins a stem.

Control Measures

 To prevent the formation of galls, trees would have to be sprayed with an insecticide labeled for Eastern spruce gall just before the new growth begins to open. Timing is critical since once the galls begin to form and the insects are inside the gall, sprays will be ineffective. A second spray in the fall after the galls have turned brown and have cracked open will also help control the problem.  

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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