oak tree with raised red growths
Hello Rick and Debbie,
Those growths on the leaves of your red oak are galls probably caused by cynipid wasps. More than 800 species of the cynipid wasp lay their eggs on oak leaves. The insect causes abnormal growths, called galls.
This question was answered previously by an MSU Entomologist which I am attaching.
He is referring to a different gall, but the same information applies to the ones that you are seeing.
I hope this answers your question.
Thank you for contacting Ask an Expert.