We recently moved into a new apartment and have a very large tree that hangs over our patio. The tree has started to lose its leaves and we have noticed that there seem to be growths on the leaves? Is the tree diseased?
The Gardener’s Answer
Hi Dahlia: The picture that you sent is pretty classic sample of galls on hackberry foliage. Galls are formed when plant tissue swells as a result of insects, mites, fungi, and/or bacteria. There are several different types of galls and gall-makers; they all have specific host plants. Hackberries are hosts to a few different species but from your picture it appears that your tree has nipple galls caused by a psyllid species or jumping plant louse. The galls are formed as the insects feed on the foliage. It is not aesthetically pleasing but in most cases it does not affect the overall health of the tree. Like you mentioned, the foliage will likely drop prematurely. In terms of control, it is a good idea to clean up all fallen foliage to decrease next year’s population. At this point the adults are emerging and preparing to find warm homes to survive the winter. Chemical controls are not typically necessary since the galls do not cause serious harm to the tree.