My hedge is unhealthy this year. The leaves have holes in them but I haven’t spotted any bugs, although they may be there. Any idea what could be causing this. Hedge is about 150 feet long and 7 feet high and most of it is affected.
Thank you for contacting the Toronto Master Gardeners with your inquiry.
Your hedge certainly has undergone severe insect damage. It is difficult to give you a solution without knowing what type of insect is causing the damage. You mention that you are unable to see any insects. Have you checked the bark or the lower leaf surfaces for any signs of infestation? Pests such as earwigs and slugs only feed at night. My suggestion would be to take a flashlight and check the foliage towards dusk. If earwigs are the culprit then you will find solutions on treating these pests on one of our archived posts titled Bug
You never mention what kind of hedge it is and from your photo it is difficult to tell leaf arrangement, however I believe that your hedge is Privet (Ligustrum). If you do indeed have a Privet hedge this link lists the possible pests of privet hedges.
With such a large hedge you might consider bringing in a certified arborist for his professional opinion. To find a certified professional arborist visit the Ontario branch of the International Society of Arboriculture here.