Erineum Patches may be found on the upper or lower leaf surfaces of several species of deciduous trees in Ohio. They are considered a type of plant gall and their general appearance accounts for common names such as velvet galls or felt galls.
The fuzzy patches appear in many colors from silver to subtle shades of green to obvious shades of yellow or red. In fact, some patches may pass through this entire color range as they develop. Most will eventually turn brown to black. Their colors and general appearance sometimes causes them to be mistaken for a leaf spot or rust disease.
A close examination will reveal the erineum patches are comprised of tiny hairs growing from the leaf epidermis. An even closer examination using a microscope may reveal eriophyid mites (family Eriophyidae) cavorting among the hairs; the mites are the culprits behind the patches.