When I first learned about hackberry nipple gall during my undergraduate degree at Iowa State University, I snickered. How could you not? We were in our woodies class (ha!) [woody plant materials for those of you who are more mature than me] and I'm fairly certain it was at the point in the semester where we were all looking for a good laugh.
|Hackberry nipple gall in all its glory.|
|Look at those galls!|
|Adult hackberry psyllid on the tip of a pencil. Photo by B. Ogg.|
In spring, the adults will lay eggs on emerging hackberry leaves and the young nymphs will feed on the leaf tissues. The tree responds by creating a gall, which is simply abnormal growth. The nymphs spend the rest of the summer sucking plant juices in the comfort of the gall until they pupate in the fall as an adult and emerge to overwinter and start the cycle again.
|The gall is a comfortable cocoon for the hackberry psyllids to spend their summer.|
|A hackberry tree that has shed many of the afflicted leaves in late August.|
Nipple gall would not be a reason to stop planting hackberry--this tree has so many benefits. As my co-worker Eric Hammond described: it's reliable...like your friend with a truck. It's drought tolerant, has good yellow fall color and is tolerant of many soil types and urban conditions. The nipple gall just provides a great conversation starter when you have friends for dinner. "Hey Joe! Let me show you the nipple gall on my tree!"