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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 eyespot gall on red maple leaf poplar twiggall fly larva
Galls on red maple caused by mites. Eyespot gall on red maple. Poplar twiggall fly: pupa emerging from gall.
corky bark disease on quaking aspen crown gall blade spruce gall adelgid
Corky bark disease on quaking aspen. Crown gall. Blade spruce gall adelgid.
leaf gall oak apple gall galls on oak
Leaf gall caused by Eriophyid mite on plum/cherry. Oak apple gall. Galls on oak.

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Identification and Control Information (each will open in a new window)


[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,]

It is the policy of the State of Maine to minimize reliance on pesticides. The Maine Department of Agriculture and the Maine IPM Council encourage everyone to practice integrated pest management and to use pesticides only as a last resort. The mention of pesticides in the fact sheets linked to these pages does not imply an endorsement of any product. Be sure that any product used is currently registered and follow all label directions.