Walnut blister mite; the 0.1 mm mites hibernate in the leaf buds of the walnut.
Also known as:
Walnut leaf gall mite
Walnut blister mite(Aceria erinea). The 0.1 mm mites hibernate in the leaf buds of the walnut and infest the leaves as soon as they sprout. The walnut blister mite causes caterpillar-shaped galls (bumps) on the leaf and on the underside cavities with brown hairs. Between the hairs live the mites. The galls vary in size between one and two and a half cm.
The damage is mainly aesthetic.
Some bugs eat mites, so do not chase away bugs.
In case of large-scale infestation during the season, spraying pyrethrum on the still bare wood at the end of the winter of the following year can help prevent large-scale infestation.