Tree Care Tips: Cooley Spruce Galls
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The growths are actually Cooley Spruce Galls, pictured above, and they are caused by an aphid like insect called the Cooley Spruce Gall Adelgid (Adelges cooleyi). While they are not harmful to the tree's health, left unchecked they can quickly multiply, turning an otherwise stately looking tree into a brown, unsightly mess.
A long term remedy for ridding the tree of the galls starts by understanding the adelgid's life cycle. They begin their lives as nymphs that overwinter on the tree's branches. In spring they mature and begin to lay eggs. The young hatch and begin feeding on sap, forming the gall as protective covering.
Early season galls are green in color, later turning brown. In late summer or early fall, the young emerge, ready to begin their own life cycle.
Catching the problem at an early stage helps disrupt the life cycle. The application of a dormant oil, also called a horticultural oil, in early spring or late fall, when the trees are in their dormant stage, often solves the problem. A new generation of organic dormant oil products have made their way to the market that work equally as well as the traditional petroleum based products.
When applied during early spring, it's easy to check the application success rate by monitoring the tree for new green gall growth. If new galls are detected, they can be removed.
Recheck the tree during early fall for brown galls, and reapply the dormant oil to deal with any potential overwintering population.
© 2009. Patricia A. Michaels