According to Michele Warmund from the Missouri University College of Agriculture, Food and Natural Resources, galls on oak trees, frequently seen in autumn months, are harmless. Galls appear as round, brown growths, especially prevalent on oaks. Warmund has had inquiries about the growths from property owners and thinks that the unseasonably warm spring may have contributed to the increase in the production of galls this year. Property owners want to know if they should spray insecticides or trim trees to try to get rid of the galls. She says, “Do nothing. Just sit back, relax, and enjoy them. Mother Nature will probably take care of them as leaves drop and insects seek shelter underground during the winter.”
Oak galls are caused by a gall midge, which looks like a long-legged fly. Whey they first form in the spring, they are magenta or red. In the fall they turn brown and crusty, and at that time the gall bursts, releasing a larvae that buries into the soil to overwinter while pupating. In the spring, adults emerge to lay eggs and start the cycle over again.
Galls can also be found on other plant species like hickory, walnut, chestnut, and elderberry.