A breakdown of the Hackberry Nipple Gall with UI Extension


Champaign, Ill. (WCIA)

Ryan Pankau is a horticulture educator with the UI Extension, serving Champaign, Ford, Iroquois and Vermilion counties and he’s back with a unique plant native to Illinois.

The hackberry nipple gall is quite common across the Midwest on our native hackberry (Celtis occidentalis) trees. I think most people have noticed this gall in their lifetime due to its widespread distribution and noticeable, bumpy appearance when present. I can remember picking this gall off of many leaves for further inspection when I was a kid without ever figuring out the weird bumps.
The insect responsible for this gall is the hackberry psyllid (Pachypsylla celtidismamma). Each spring, adult psyllids (pronounced “sill-ids”) lay their eggs on the emerging leaves of hackberry trees. After hatching, the young psyllids begin feeding on leaf tissue, sucking sap right from the leaf.
As a defensive response, the leaf initiates abnormal growth around the psyllid to contain the pest by producing the galls we see on the leaves. Over the rest of the summer, the psyllids comfortably feed on sap from inside their protective gall.
In reality, the galls and their insect roommates have a negligible impact on tree health. These insects really are not that bad at all. In fact, the adults are so small that they can actually fit through window screens when they emerge in late fall to find an overwintering location. Any that do actually make it indoors will die because our homes are not suitable overwintering sites, leaving little or no negative impact to humans other than some unattractive looking leaves.
So, the next time you see bumpy leaves up in a hackberry canopy, take a minute to ponder the fascinating floral/faunal relationship that is unfolding. There is no need for any control of these native insects, they are simply part of our central Illinois ecosystem.

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