Ash leaf gall midge

The Ash leaf gall midge (lat. Resseliella clavula) is a small dipteran insect belonging to the Cecidomyiidae family. It is a specific pest that targets ash trees (Fraxinus spp.), causing the formation of distinct, club-shaped galls on the leaf petioles of the host plants.

The primary host for this species is the European ash. The damage is most concerning in nurseries and young plantations where aesthetic and physiological health is crucial. While mature trees can typically tolerate infestation, severe outbreaks in young trees may stunt growth and compromise their overall vigor.

The biological cycle is synchronized with the spring development of ash leaves. After overwintering in the soil as pupae, the adults emerge to mate. Females lay eggs on the young leaf stalks. Upon hatching, the larvae penetrate the plant tissue, triggering the host plant's defense mechanism to form a protective gall, where the larvae feed.

The damage is identified by visible, elongated, club-like swellings on the petioles. As larvae feed inside, the vascular system of the leaf is disrupted. This results in localized chlorosis, premature senescence, and the eventual dropping of leaves, which can reduce the tree's photosynthetic capacity if the infestation is heavy.

• Sanitation practices including the raking and burning of infested leaf litter to reduce pupal populations.
• Application of systemic insecticides timed precisely with the adult emergence phase in early spring.
• Maintaining healthy tree growth through proper irrigation and soil nutrient management.
• Encouraging natural predators and parasitoids that help regulate the population density of the midge.