Alder gall mite

Systematic position: The alder gall mite (Eriophyes laevis) belongs to the order Acariformes and the family Eriophyidae (four-legged mites). These are extremely small, microscopic pests that are highly specialized in their choice of host plants, typically restricted to certain species of trees.

Crops damaged: The primary hosts for this mite are trees in the genus Alnus, commonly known as alder. It is a monophagous pest, meaning it does not typically jump to other tree families, focusing its impact specifically on black and grey alders.

Biology and life cycle: Adult females overwinter in bark crevices or under the scales of buds. When the buds break in the spring, the mites emerge and move to the young, developing leaves. By feeding on leaf cells, they induce the plant to form galls, which serve as both protection and a food source for subsequent generations of mites throughout the growing season.

Damage and harmfulness: The most visible symptom is the formation of numerous small galls on the upper leaf surface. These galls appear as reddish or greenish pimples. While not usually lethal to mature trees, heavy infestations can cause premature yellowing, leaf drop, and reduced physiological vigor, which may stunt the growth of young trees.

Protection measures: Management of the alder gall mite requires careful timing of interventions.

• Application of specific acaricides during the early spring migration period.
• Sanitation practices such as raking and destroying fallen leaves to reduce overwintering populations.
• Pruning and removing severely infested branches to prevent further spread.
• Promoting healthy tree growth to increase resilience against mite attacks.