Welcome Harryhornet!
I don't know anything about privet hedges, but I did find the following info and wondered if its similar to the problem you're having?
~Q. We have a Privet Hedge, approx 7 ft by 2-3 ft. Unsure of it's age. Early spring after the spring growth had appeared, 2 plants curled up & died. They had lost most of their leaves the previous autumn, however when they sprouted in the spring we thought all was OK. We had cleared all the ivy from around the base of the plants the year B4 & thought maybe this had had some effect. Now it seems that part of 2 other hedges are also starting 2 die. They R not anywhere near the 2 plants that died in the spring. Somebody suggested it was because of a lack of water over the summer, however one of the hedges is situated behind our herb garden and so was watered regularly during the summer. The leaves now are a mix of dark purple / red and yellow / brown. Some of the plants show some new green growth, others don't. They appear to have thinned out quite considerably too as we can now see through to the other side. Some of the old wood has a green soft coating to it, like a thin moss.
Also a few months back I noticed some of the leaves had curled up on themselves and turned black, with further investigation I found a small cream coloured larva (3mm) inside the leaf walls surrounded by what seemed to be digested black remains of the inside of the leaf. I have not been able to find help anywhere on what this might be. It doesn't leave tunnels like a leaf miner, rather it just seems to eat everything in between the 2 walls.
Please I don't know what to do next. I feel we are in danger of losing all the hedge. It was last pruned late spring / early summer and we've been afraid to touch it since then. I have noticed a few other hedges in the district looking somewhat the same, but there are others which look fantastic. Is it worth putting down some Sequestered Iron or spraying with a fungicide?
A. I think the leaf miners you found are incidental rather than the cause of the problem, they are not uncommon on privet. It sounds like either honey fungus or wilt (a wonderfully vague term), both are fungal diseases that will readily attack privet and cause the symptoms you describe and over the time scale you describe. If it is honey fungus, you should be able to find some of the bracket-like fruiting bodies on the trunks of the plants. Wilt is caused by one of a group of fungi that give no outward signs other than the symptoms of the plant that is suffering.
In either case there is little you can really do directly. Cut out all of the dead wood and stems and burn them, clean pruning tools carefully afterwards so not to spread spores. Clear under the plants of weeds, ivy, dead leaves and any other debris and give the hedge a top-dressing of fish blood and bone meal lightly forked in to help build up the strength. I have to say though that the outlook is not very positive, particularly as you say other hedges in the area are affected, it seems like the disease is endemic and may re-infect.
Try my suggestions, but be aware that you may eventually have to replace the hedge with something that has resistance to the disease that is affecting it.~
Anyone else with any ideas on what might be wrong with HH's privet?
