Oaks are host to majority of galls but other trees and shrubs affected as well. Galls of certain inciters have a distinctive shape, occupy specific sites such as leaves, twigs and bark, and locations thereon, such as o the top or bottom of leaves, on veins, interveinal, at leaf margins and on petioles. They are unique to a specific host genus. Oak trees serve as host to a clear majority of all known and classified galls.
Galls are more of an aesthetic nature than an acute detriment to overall tree health.
People first become aware of galls only after they have developed. Although many insects or mites can be specifically identified by the unique galls associated with each species, little is known regarding most of their life cycles. Thus, the timing for applying spray treatments is imprecise for most gall-formers. Roughly speaking, gallforming insects and mites are active when leaves are unfurling and expanding. Therefore, treatment applications at this time might kill gall forming insects and mites.