Acer with die-back caused by Japanese maple scale infestations.
Close-up of an Acer branch with gloomy scale (dark circular raised) and Japanese maple scale (brownish is the underlying skin after waxy white has been wiped or worn away). Japanese maple scale are also the white kind of oyster shaped insect on the branch.
Close-up of an Acer trunk heavily infested with Japanese Maple scale.
Close-up of Japanese maple scale on a Cornus trunk. The brownish colored insects are the same scale, but where the white waxy covering has been worn or wiped away. All pictures were provided by: Brian Kunkel, Ornamentals IPM Extension Specialist, University of Delaware