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. Annual pruning and burning of galls will reduce infestations on individual trees but this is not practical for plantations. Pruning should be done in the fall when the trees are dormant and the mites are in the galls. Planting resistant clones is the best long term solution. Assiniboine', and 'Manitou' have the added benefit of being male clones and therefore do not produce seed fluff.