Recently, I received an email via our PlantClinic email with a couple of photo wondering if the pea-sized “balls” on their Texas live oaks might be “fatal” to the trees.
This is one of the few times that I get to give a happy reply. Those galls on the oak leaves are caused by insects… gall-making insects. This is quite typical on oaks in Texas. Rarely, do these galls ever kill an established tree.
I say rarely, because I remember a situation about 8 years ago when we actually found a gall made by an insect on the main trunk of a young Texas live oak. That gall actually girdled the trunk, disrupted the vascular system and eventually killed the tree. It was a small young tree ~1 inch caliper. Nonetheless, there are several different types of galls that can be found on oaks. To my knowledge (Hey I am not an entomologist…..but bugs are fun too), they are made by different insect. People have ask me questions such as “What can I do about it?” My typically answer is nothing. Some year they are worse than others but in general they just result in symptoms which may not be aesthetically pleasing. Then again, there was a time that I thought painting the larger round gall with bright colors might make the tree look more attractive, especially in the winter. That was before I realized that Texas live oak are evergreen, hence hiding the colorful balls in all that green.
Here is a link to my entomologist colleagues’ factsheet on gall-making insect. http://insects.tamu.edu/extension/publications/epubs/e-397.cfm
So to recap: gall on oaks typically do not kill an established oak. If galls are localized or limited, it is possible to remove the galls for aesthetic purposes. Otherwise, do not worry too much about it.
Thanks to C. Stoltman for the question and the photographs shown on this page.