Pest/insect covering tree

QuestionsPest/insect covering tree
donal o halloran Staff asked 7 years ago

Hi, A tree (elderberry) in our garden is covered in an insect. It a old/mature tree and all the new growth has insects covering the stems of the leaves (see photos attached). Some of the older leaves are covered in small flies. Is this harmful to the tree and what action should we take? I am a complete garden novice.