Knopper (Acorn) Gall - Andricus quercuscalicis

Symptoms: The gall wasp (Andricus quercuscalicis) convert acorns into ridged structures. This process begins around September and the yellow-green galls age over time to become brown and drop off the tree.

Cause: Caused by a small gall wasp, which lays a single egg in each gall. This is a two-part process with the sexual generation developing galls on the catkins of the Turkey Oak in spring.

Control: While there were initial fears that this would impact the ability of the tree to reproduce, there doesn't seem to be any real issues and treatment is not required.