Funny bumps on pear and plum leaves are caused by an Eriophyid mite called Pear Leaf Blister Mites. The injury may start as a reddish growth but as it matures it will turn dark brown. This is typically a cosmetic problem and once you see the problem it is too late to do much. In some cases, heavily infested leaves may distort and fall off.This article was posted in Galls, Tree Insects.
Department of Entomology