Symptoms

Little, raised red pimple bumps can be seen on the surface of the leaves.

Cause

Microscopic sap-sucking mites. They secrete chemicals back into the plant which cause the galls. There are many different mites which are specific to particular plants, such as Acer, lime and broom mites.

Harm

None, except looking unsightly.

Treatment

None. You can pick off infected leaves