QR18-SL16 – Oneonta Susquehanna Greenway

Goldenrod Galls

Rosette Gall (aka leaf bunch gall): The goldenrod gall midge lays its eggs at the top of the goldenrod stem. Midge larvae feed on the leaves and inner stem, causing them to grow abnormally and form the dense rosette. The larvae then move to the soil and burrow into the goldenrod’s rhizome, protected from freezing winter temperatures by the subterranean location, before pupating in spring.

The Gall Ball: a golf-ball-sized growth on a goldenrod stem. The female goldenrod gall fly, which lives as an adult for only 2 weeks, deposits single eggs into the stems of dozens of goldenrod plants near the terminal bud. The hatched larvae secrete chemicals into the stem, triggering gall formation. The hard outer layer protects them, while the softer inner tissue provides food. In late fall they chew a tunnel to the outer later without breaking through. Their internal water is replaced with glycerol, which serves as an antifreeze, enabling them to survive winter temperatures as low as -40ﹾF before emerging as adults in spring.

Cool fact: Adults of both species lack functional mouth parts and survive on stored energy to fulfill their one function, which is to mate and lay eggs.

View the full PDF – Goldenrod Gall Balls