Mites are active within the galls from April to October, completing a generation every 2 to 3 weeks, which results in 8 or more generations per year. From May to August, some of the mites migrate to new, unfolding leaves, where they begin feeding by sucking the plant sap. The mites are protected from predators and insecticides while inside the gall. Newly formed galls are soft and green, but later in the summer become hard and brick red. Galls may grow to 3-4 cm in diameter.
Galls tend to be more abundant on the lower branches.
Infested branches are stunted, crooked, and have sparse foliage. Several years of attack result in branch dieback therefore reducing the aesthetic and shelter value of the tree. Galls can persist on the tree for 5 years or more. Infested trees become stressed and more susceptible to secondary insects and diseases. No pesticides are currently registered for control of this mite.