Dying Privets

I have privet hedges all round my garden and they have always been thick and healthy. Now on one section of the privets, the leaves are going yellow and dying and they are now really sparse where as i can now see through them to the main road. Can anyone help me identify the problem.

 

Are they dying right down to the base? Sc.rape a tiny bit of the bark off to check if it is green and alive underneath. Start where the branches are dying and work your way down towards the roots so you can find out how much die back there is.

 

julestcb,
Did you get any resolution to this ? I have a similar problem. A few years ago a small section of the hedge died and each year 2 or 3 feet eiher side dies. I thought some kind of root fungus, as the foliage looks healthy until it dies, but when I've dug up the dead stuff the roots look fine (not that I have an educated eye). Anyone any thoughts ? I have replaced the dead stuff, but the new stuff doesn't look very healthy this year again. Although there is evidence of good healthy shoots, I know it will die back later in the year. The hedge looks awful, and if I can't sort it out I think will need to dig it all up.
JAB