Posted: 03/01/2012 at 14:54
It could simply be that the plants are short of water. Privet is a very thirsty and hungry plant, and needs regular watering in dry periods otherwise it becomes stressed.
However, there could be a more serious problem. The symptoms you describe are very characteristic of honey fungus - a fungal disease which kills woody plants - especially those that are otherwise under stress.
Sadly, the only option is to grub up the plants and burn them. To check whether it is honey fungus you should look in the soil for the black 'boot laces' or rhizomorphs with which the disease spreads. A white fungal sheath also appears below the bark of affected plants.
If it is honey fungus and you wish to replace the hedge, then try using beech, box, laurel, hawthorn or yew which show some degree of resistance. The soil should be kept clear for a year and any rhizomorphs removed before replanting.