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On the dead goldenrod stalks are round and oval-shaped outgrowths known as galls. A gall is an abnormal growth of a plant resulting from an insect or bacterial irritation. The round, one-inch galls are caused by the Eurosta Fly. The long, oval growths contain eggs and larvae from the goldenrod gall moth. Eggs were laid within the stem causing an irritation which stimulated plant cell production. A cozy home formed for the larvae. Before they developed into the flies, they ate their way out—look for the small holes in the old galls.
cross-section of Gall