Gouty oak gall was numerous last year and is still common. They are numerous in Fulton County. Typically, such native insects are very common for about 3 years, followed by low numbers for 7 or 8 years.
Gouty oak gall appears as a woody, gnarled gall up to 2 inches across that circles small branches and can girdle them, killing the branch out past the gall. Its life cycle is 2 years, with the first year less conspicuous on leaves and twigs. The adult stage is a tiny wasp and attacks scarlet, red, pin, and black oak.
On small trees, prune off the galls and destroy them, particularly in the northern two-thirds of Illinois, where they are usually less common. Their killing of branches can cause trees to become misshapen. Pruning may not be practical in southern Illinois, where the galls are more common. Particularly in locations with large numbers of infested oaks nearby, removing galls may have little effect, with more damage done by the pruning than the galls. Nurseries and others with many small oaks may wish to spray the trees with dimethoate (Cygon) in the spring when leaves are expanding. Treatment may reduce the number of twig galls but won't be noticeable for 2 years because these galls have 2-year life cycles.
In general, if the tree is too tall for you to reach the galls and prune them, the problem can be ignored. Mature trees can contain thousands of galls without major branch loss. Heavily attacked trees appear to be as healthy and long-lived as those that are not attacked.