Hello,

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.  Their appearance is not affected by the weather.

This question was answered previously by an MSU Entomologist which I am attaching.

https://ask.extension.org/questions/419681

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.