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Spruce Gall Adelgids

September 15, 2004

Eggs of Cooley spruce gall adelgid and eastern spruce gall adelgid hatch in late September in central Illinois. In southern Illinois, they hatch in mid September; in northern Illinois, in October or early November. Once they hatch, they are vulnerable to sprays of carbaryl (Sevin), imidacloprid (Merit), insecticide soap, summer spray oil, and other insecticides for several weeks as they overwinter as young nymphs.

In the spring, their feeding causes the host to form a gall around the insects that protects them from insecticidal control. At the end of a twig, a Cooley spruce gall adelgid causes a gall to form that looks like a spruce cone about one-inch long, with needles protruding from it. The eastern spruce gall adelgid causes a similar gall to form, but it is typically only about 1/2 inch long and occurs at the base of a twig. The eastern spruce gall girdles and kills the twig protruding from the gall. The galls of both species are initially green but turn brown by late spring. Holes open next to the needles, allowing the adult aphidlike adelgids to fly away to lay eggs.

Spruces commonly have low numbers of these galls that typically do not warrant treatment. However, heavy numbers greatly restrict tip growth, causing limited tree growth, warranting treatment.

Author: Phil Nixon


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