Horned Oak Gall: FAQs From Homeowners
If you have an oak tree, you might be unnerved to find a big, swollen, horned mass within its branches. It can look like something out of a horror film, making you cringe and worry for your oak tree. Chances are, what you've discovered is a horned oak gall. They are not uncommon, and their appearance makes them look worse than they really are. Here are some questions homeowners usually have when they discover one of these growths.
What causes a horned oak gall?
There are some old wives' tales that say these galls are like a cancer of the oak tree, but that's not accurate. Horned oak galls are actually caused by wasps. A specific species of moths lay their eggs just under the bark of the oak tree. Those eggs eventually hatch into larvae, which cause the wood around them to swell and expand into the gall. The largest of galls can be several feet across. The size mostly depends on how many wasp larvae are inside.
What will happen to the larvae?
Eventually, usually in mid-spring or early summer, the larvae will start turning into adult wasps. They'll then emerge from the gall. When the gall is empty, it will start to shrivel up and turn gray. At this stage, the gall may start to resemble a typical wasp's nest, but the horns and the fact that it is part of the oak branch make it distinguishable.
Should you remove horned oak galls?
Experts usually recommend against removing horned oak galls. Doing so puts you at risk for wasp stings, and it is easy to do more harm than good to the tree in the process. Even the largest oak galls don't actually do much harm to the oak tree, as ugly as they may be.
How can you prevent future horned oak galls?
It is worth taking preventative steps to prevent the wasps from creating more galls on your oak tree. The easiest approach is to have a tree care company come spray the canopy of your oak tree with insecticides. These insecticides will kill and repel adult wasps so they don't lay eggs on oak branches. Another option is to have the tree injected with insecticides, which will kill any larvae as they hatch.
Now that you have a better idea of what's wrong with your oak tree, you can relax. Horny oak galls are ugly, but not that dangerous — and there's plenty you can do to prevent more from forming.