Sometimes our ornamental trees will form off growths that will concern homeowners. Certain midge flies, mites and wasps cause plant tissues to form abnormal growths or galls. Galls have distinctive shapes and occupy specific sites such as leaves, twigs and bark. Each gall is unique to a specific host genus. There are more types of galls found on oak trees than any other plant group. Galls normally do not affect tree health.
Although many insects or mites can be specifically identified by the unique galls, little is known regarding most of their life cycles. Thus, the timing for applying spray treatments is imprecise for most gall-formers. Roughly speaking, gall forming insects and mites are active when leaves are unfurling and expanding. Therefore, treatment applications at this time might kill gall forming insects and mites. Spray treatments after galls have been formed and noticed would be of little use. Pruning out stem and twig galls, where practical, may result in reducing the numbers of future galls.
Since galls rarely cause significant damage to trees and control difficult, spray treatments are not recommended.
