Ash gall mite

Systematic position: The ash gall mite (Aceria fraxinivora) belongs to the family Eriophyidae within the order Acariformes. These microscopic, worm-like mites are specialized plant parasites that induce the formation of abnormal growths known as galls on their host trees.

Crops: This pest exclusively affects trees of the genus Fraxinus, particularly the European ash (Fraxinus excelsior). It is commonly found in urban forestry, landscape plantations, and forest margins where ash trees are abundant.

Biology and life cycle: Adult females overwinter inside dormant buds or under bark scales. As the tree breaks dormancy in spring, the mites move to developing flower buds. Their feeding triggers the host plant to produce deformed, cauliflower-like masses, inside which the mite colony feeds and reproduces throughout the growing season.

Damage and economic significance: The primary damage manifests as large, woody, or fleshy galls that replace the normal inflorescences. While rarely lethal to a mature tree, severe infestations cause significant aesthetic decline, nutrient diversion, stunted shoot development, and potential branch dieback in stressed specimens.

Control measures: Management of the ash gall mite is challenging due to the protective nature of the galls. Recommended strategies include:

• Pruning and destroying affected branches during the dormant season to remove the overwintering population.
• Applying systemic or contact acaricides at the early bud-burst stage when mites are migrating to new growth.
• Improving tree vigor through proper irrigation and fertilization to help the tree tolerate existing damage.