Rough Bulletgall Wasp- Bumps on oak tree

This is a tiny gall wasp that causes galls to form on Bur oak and white oaks.

Identification

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.

Life Cycle

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.

Damage

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.

Management

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.