Walnut blister mites

Symptoms

The feeding activity of the mite causes an irritation to the leaf tissues, which results in the plant producing the blister-like structures. The blisters cause little damage to the tree. The damage is primarily aesthetic as it only impairs the visual beauty of the tree. The mites can also infest the green husk of the nuts causing a russeting or blackening of that tissue.

Spot them

The blister mite is microscopic in size, and you need at least a 10 x magnification to see the mites crawling among the hairs in the blister on the undersurface of the leaves. The mites are creamy white and cigar-shaped.