Oak trees
Irregular plant growth which is stimulated by the reaction between plant hormones and powerful growth regulating chemicals produced by a gall wasp.
Horned Oak Galls are hard, woody swellings on oak twigs. Small horns protrude through the surface of the gall, and a single gall wasp develops in each horn.
This gall is known to cause economic damage and, in some cases, if left unchecked will cause death of the tree. Pruning the galls off the tree in May, when the wasps are inside, is the only known effective control.