Though a large number of insects attack the various kinds of oaks, few can ordinarily be regarded as serious pests. If caterpillars are feeding on the leaves, spraying with a stomach poison is usually a sufficient treatment. Borers in the trunk can be handled as suggested for the maple borer, and sucking insects can be controlled by spraying where they are with a contact poison. Gall insects, however, may cause perplexity, as neither of the methods just named would seem to fit this case.

It is very unusual for gall insects to be so abundant on a tree as to render it liable to die. It is very common, however, for them to disfigure the tree and thus lead to a desire for treatment. In cases where galls are formed on the branches they are likely to become permanent eyesores, and such branches should be promptly cut off and burned. Elsewhere on the tree there is little which it will pay to do, and patience will usually be rewarded in a year or two by the disappearance of the galls, as their makers are gradually overcome by the natural enemies of these insects.