Common spangle gall - Neuroterus quercusbaccarum

Symptoms: Develops on the underside of the leaves of pedunculate oak (Quercus robur) and sessile oak (Quercus petraea). The discs begin as yellow-green and age to become reddish.

Cause: Caused by a small gall wasp called Neuroterus quercusbaccarum. These galls are created when the wasps of the currant gall generation emerge and lay their eggs on the underside of the leaves. The offspring of these eggs will emerge around April and the cycle will begin again.

Control: There doesn't appear to be much stress on the tree, so can be left in place. Also there can be many galls on each tree, making it very difficult to keep under control.