Did you Know?Many types of insects and mites can cause galls (abnormal outgrowths) to form. Various species of mites, wasps, flies, adelgids, and sawflies can induce gall formation by injecting certain chemicals into the plant tissue that initiates the abnormal growth. These chambers provide habitat/protection and food for the developing insect or mite. Some gall makers are so efficient that their galls are actually "resource sinks" that pull in extra nutrients for the gall maker.
Rough Bulletgall Wasp- Bumps on oak tree
This is a tiny gall wasp that causes galls to form on Bur oak and white oaks.
In Colorado, this insect can cause extensive damage to oak trees, essentially covering the branches in small, globular galls. Infested trees are very noticeable in the winter when leaves are not present.
Gall insects have a somewhat complex life cycle. Eggs overwinter in dormant buds towards the terminal end of branches. In the spring, they create a minute gall resembling an enlarged bud scale. After completing development, they emerge and oviposit eggs in the stems of current season’s growth. This is when the larger galls are formed along the branches of oaks. These wasps emerge around October and lay eggs in the dormant buds before winter.
In Colorado, these gall wasps cause extensive galling along branches that can severely stress trees and even kill them after heavy, repeated infestations. The galls appear as a woody, globular growths around branches. These brown galls can appear darker and almost black as sooty mold will sometimes grow on sugary honeydew that is excreted from these galls.
Tree susceptibility to these bulletgall wasps is highly variable. It is not uncommon to see a bur oak covered in these galls next to another bur oak that is completely gall-free. There are a lot of parasitic wasps that attack bulletgall wasps. For this reason, you should not remove the galls since parasitoids may have successfully parasitized the gall wasps and are developing inside the galls.
Unfortunately, there are not effective chemical control options for bulletgall wasp.