Most galls pose little threat to tree health but horned oak and gouty oak gall infestations can be a significant problem on pin oaks - disfiguring them, weighing down the branches, and eventually even killing the trees. While several control approaches have been evaluated and others are in progress, there is no specific recommendation at present.
One confounding factor is the nearly 3-year life cycle of the tiny wasp that causes these galls; most of that time is spent in woody galls ranging from small and inconspicuous to mature galls the size of golf balls. It is very difficult to spray tall trees, and one would have to do this 3 years in a row, just before buds show green tips in spring in an attempt to break the life cycle. So far, there has been little success getting systemic (e.g, soil-applied or trunk injected) insecticides to translocate into the woody galls. When feasible, pruning out soft and alive (greenish-brown) galls from lightly-infested trees may be worthwhile. Dried up brown galls are already “spent” and pose no threat.
Gouty Oak Gall. Photo from Michael Masuik, Penn State University
Horned oak gall. Photograph by: USDA Forest Service, www.forestryimages.org Reprinted from "Horned Oak Gall/Gouty Oak Gall - No Good Control Recommendation" By Dan Potter and Lee Townsend, University of Kentucky in the current edition of the Kentucky Pest News.
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