Aceria caulis

Erineum anomalum
Juglandis caulis
Acarus caulis

Hosts: Juglans nigra

Relationship: The mites produce the Petiole Gall, peculiar reddish to purplish erineum-covered wooden swellings on the petioles; leaves often distorted and shortened; may be many galls per leaf.

Range: IL, GA, MD, NJ, NY, OH, PA, WV

This is an exceptionally interesting and beautiful pubescent gall, often brightly colored, passing from greenish through pink and crimson to reddish brown. The gall most frequently develops as an irregular, solid, hard mass on the leaf petiole. It is often solitary and variable in size. The exterior is covered with a dense mass of silky, unicellular, erineumlike hairs (see pl. 7, A). The gall tends to be large and to spread to and partly envelop the stem and leaf. The affected structure is greatly distorted and twisted, and leaflets fail to develop. This mite was found infesting black walnut in New Jersey and Pennsylvania in July-August. It is probably distributed throughout the range of its host from Ontario to Massachusetts and south to Florida and eastern Texas.