bark disease on elm

bark disease on elm

Observation - bark disease on elm - UK and Ireland. Description: This young elm tree is affected by (presumably) Eriophyid mites. However, does anyone know what causes the bark to become corky (red arrow)? I've seen that phenomenon on a number of sites, and also on hawthorns. Is this a viral, bacterial or fungal infect

This young elm tree is affected by (presumably) Eriophyid mites. However, does anyone know what causes the bark to become corky (red arrow)? I've seen that phenomenon on a number of sites, and also on hawthorns. Is this a viral, bacterial or fungal infection?