Galls are abnormal growth on plants. They are caused by the feeding of living organism, most often insects, but also bacteria, fungi, nematodes and mites, on the plant. Although these growths may be unsightly, they usually do not affect the health or vigor of the host plant.

red maple leaf with galls
Galls on red maple caused by mites.

eyespot gall on red maple leaf
Eyespot gall on red maple.

poplar twiggall fly larva
Poplar twiggall fly: pupa emerging from gall.

corky bark disease on quaking aspen
Corky bark disease on quaking aspen.

crown gall
Crown gall.

blade spruce gall adelgid
Blade spruce gall adelgid.

leaf gall
Leaf gall caused by Eriophyid mite on plum/cherry.

oak apple gall
Oak apple gall.

galls on oak
Galls on oak.

Click on images to view full-size

Identification and Control Information

[Photos, left to right: Steven Katovich, USDA Forest Service,; Clemson University - USDA Cooperative Extension Slide Series, ,; Whitney Cranshaw, Colorado State University,; William Jacobi, Colorado State University,; Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services,; Gyorgy Csoka, Hungary Forest Research Institute,; Steven Katovich, USDA Forest Service,; James Solomon, USDA Forest Service,; John H. Ghent, USDA Forest Service,]