The lichen itself is not particularly significant. A photograph would be helpful, but more info is essential to even take a guess at what might be wrong. Are there signs of other problems such as insect infestation, scale on the woody stems or leaves, fungal infection? Silvery, dull appearance to upper leaf surfaces? Damage at the base to the woody stems? How old is the hedge? Was it healthy last year? Have you suffered severe drought this year...

The disease will spread through the whole hedge. You need to dig it all out and start again after drenching the soil with Armillatox.

Whoa, Doctorbob! Which disease is that?

Thanks very much for the advice so far.

The hedge is ~ 50 years old & we have never had to water it. It has been dying slowly for ~ 3 years & we have been remiss in not sorting it out earlier. The orange/grey lichen like substance is only on the wood parts. There are no insects & there is nothing on the leaves that are left. There are no fungus signs i.e. no black bootlaces at the base or 'toadstools' around. We have had drought this year but this only ever slowed growth & never killed anything. Sorry Have not got a picture yet.

I suspect it is rust, very common disease on privet, which has been widely used on many housing estates as a fast growing hedge easy to maintain. There will also be coral spot on much of the dead pieces near the base. Trying to kill it off in the hedge itself will only result in some alive and some dead. As it is 50 years old it's best to take it all out, clean the soil as suggested and in the spring replant with another sort of hedging after fertilising and composting the area.

Thanks Doctorbob1 (& Bamboo). I am going to need something that grows very fast & will keep leaf all year - what do you recommend for me to use to replant?

Don't know where you live - Griselinia would be good, but won't work in colder parts of the country. Lonicera nitida, either plain green or 'Baggesen's Gold', Photinia, Escallonia, Pyracantha if you don't mind a thorny devil, Berberis darwinii (prickly leaves, but not too bad to handle).