Galls are irregular plant growths produced in response to some insects or mites. Oak trees are hosts to a large number of different galls. These may occur on leaves, bark, flowers, buds, acorns, or roots. Leaf and twig galls are most noticeable. The gall-maker benefits by feeding on the gall tissue and also gets some protection from natural enemies. The tree usually is not harmed, although there may be some premature leaf drop. Important details of the life cycles of many gall-makers are not known, so specific recommendations to time control measures most effectively are not available.

Gall-makers must attack at a particular time in the year to be successful. Otherwise, they may not be able to stimulate the plant to produce the tissue that forms the gall. Generally, galls begin at about "bud break" as new leaves begin to unfold in the spring. Insecticide applications at that time may reduce gall formation. Contact your local Cooperative Extension office for insecticide recommendations.