We have a beech hedge in front and back garden, it is covered in something like greenfly. At the moment cannot even trying cutting it, as there are millions of these flys on it. What would you suggest, we have tried spraying with suddy water, and spray to kill greenfly cannot remember the name of the spray, but because there are so many, nothing seems to work.
It can make a hedge look messy but rarely causes much damage in the form of dieback. Leave it be and the colonies will decline or spray with a garden insecticide, ideally a systemic.
It usually does not re-appear each year but it can for a few years and make cause damage.