Stenacis triradiatus

Triradial willow mite

Description

Stenacis triradiatus (= Stenacis triradiata), commonly known as the triradial willow mite, is a microscopic mite found primarily on willow species (Salix spp.), such as Salix alba, Salix cinerea, and Salix caprea. This monophagous mite forms characteristic galls on willow shoots, creating twisted, densely clustered growths known as "witches' brooms." It overwinters under bud scales and becomes active in spring, infesting young leaves, shoots, and catkins. The feeding activity causes distortion and clustering of shoots, leading to weakened branches that impact the plant's aesthetic appeal and overall health. This damage is visually distinct from other mite species as it creates thick, tangled masses rather than the typical leaf discoloration or spotting associated with related species. Stenacis triradiatus is distributed across Europe, particularly in areas where willow species are common.

Symptom

On infested shoots and branches of willows, there are twisted and densely clustered growths. These clusters of small leaves are often clearly visible even from a distance.

Tree Species: Willow

Part of a plant- attacked: Branch

Pest significance: Less harmful

Pest Category: Mites

Invasive Species: No

Present in EU: Yes