Willow gall mite

Systematic position: The willow gall mite (Epitrimerus salicobius) belongs to the order Acariformes and the family Eriophyidae. These are microscopic arachnids with a slender, worm-like body shape. Unlike many other mites, they possess only two pairs of legs, which is a distinctive feature of the Eriophyid family.

Host plants: This pest primarily affects various species of willow (Salix). It is a common problem in nurseries, landscape gardening, and plantations where willow species are grown for ornamental purposes or erosion control. The mites tend to concentrate on the youngest, most actively growing parts of the plant.

Biology and life cycle: The lifecycle of Epitrimerus salicobius is closely synchronized with the phenology of its host. Adult females overwinter in bark crevices, bud scales, or protected areas on twigs. As soon as bud burst begins, the mites emerge and move to the developing leaves to feed and reproduce. They can complete multiple generations in a single season, with population numbers peaking during warm, humid conditions.

Damage and severity: Mite feeding causes characteristic symptoms including leaf distortion, leaf curling, and the formation of small galls. These deformations significantly impair the tree’s photosynthetic efficiency. Severe infestations result in stunted shoot growth, premature defoliation, and a weakened overall plant health, which may leave the tree susceptible to secondary pathogens.

Protection measures: Managing this pest requires a strategic approach to maintain tree health and reduce mite density:

• Pruning and destroying heavily infested branches to reduce the overwintering population.
• Maintaining proper plant spacing to ensure good air circulation and lower humidity around the foliage.
• Applying acaricides during the early spring when mites are migrating from wintering sites.
• Regular monitoring of new growth to detect early signs of infestation and initiate timely treatment.