Maple gall mite

Systematic position: The maple gall mite (Aceria macrorhyncha) belongs to the class Arachnida, order Acariformes, and the family Eriophyidae. These are tiny, worm-like mites that are invisible to the naked eye and strictly dependent on their host plants to form galls.

Host plants: The primary host for this species is the Norway maple (Acer platanoides). While it rarely kills the host, its presence is a common concern for arborists, landscapers, and homeowners who value the ornamental appearance of maple trees in parks and urban settings.

Biology and life cycle: Adult females overwinter in sheltered areas, such as under bud scales or within deep bark crevices. As soon as the maple buds break in the spring, the mites migrate to the newly emerging leaves. They feed on the underside of the leaf, injecting saliva that triggers the host plant to produce gall tissue, which then serves as a nursery for the next generations.

Nature of damage and economic importance: Infestation is characterized by the formation of small, horn-like or cone-shaped galls on the upper surface of the leaves, often reddish or purple in color. While the damage is primarily cosmetic, heavy infestations can cause leaf curling, early senescence, and defoliation, which can stress the tree and reduce its overall aesthetic value and vigor.

Control measures: Management of Aceria macrorhyncha focuses on cultural and chemical practices. Maintaining tree vigor through proper watering and fertilization is the first line of defense. Cultural control involves removing and destroying fallen leaves to reduce the overwintering population. If damage is severe, applying dormant oils or specific acaricides in early spring, just as the buds begin to swell, can significantly reduce mite populations.