Cooley Spruce Gall

Cooley Spruce Gall - Visibly affecting Spruce.

The brown cone looking structure on the tip of a spruce branch is called a Cooley Spruce Gall.
Photo: Cheyenne Urban Forestry

                                      
                                             Winged adult Cooley spruce gall adelgids emerging in late July.
                                                                                                         Photo: Cheyenne Urban Forestry

The insect (adelgid) causing this damage is a type of woolly aphid.  The young nymphs (not fully developed adults) begin feeding at the base of newly emerging leaf needles on spruce branches in the spring.  The feeding causes a distortion of growth on the newly developing branch shoot, which grows around the feeding nymphs.  The affected branch tip swells and becomes purple tinged.  The nymphs mature in July as the gall begins drying out.  When dry, the galls shrink and openings develop at the base of the now brown dry needles and branch tip.  The adult adelgid molts to a winged adult form and flies to a Douglas-fir tree and begins sucking the sap from needles now in the form of a woolly aphid.  Most of the adelgids have a complete life cycle in different forms using the Douglas-fir and the spruce. Some adelgids will complete a life cycle on just the spruce.

Generally, this insect does not cause significant harm to the trees.  The galls on the spruce trees can be unsightly.  The formation of the galls on the tips of the branches will generally kill that shoot for further growth, which stimulates growth from other buds or small branches on the same limb.  So the galls can actually give the tree fuller a more dense leaf crown area.  The developing galls, with the insects inside, can be snapped off by hand and thrown away when the tip of a developing branch is swelling and tinged in purple. Although the insect is gone, the dry galls can easily be snapped off by a gloved hand to clean up the appearance of the tree.

Chemical treatments can be made in early April using a carbaryl insecticide (Sevin®), permethrin (Astro®), or horticultural oils.  Soil injected insecticides such as imidacloprid (Merit®) may reduce the insect damage the following spring.

Links:

Colorado State University Cooperative Extension

University of Wyoming - Cooperative Extension Service, publication B-1035 is particularly helpful for tree care. This online publication contains information on: Aphids, Borers, Cottonwood blotch leaf miners, Cytospora canker, Fireblight, Gall makers, Aspen leaf spots, Oystershell scale, Pear slugs, Powdery mildew, and Spider mites.