Is this damage restricted to a single area? And could you post a photo taken a more of distance that shows the whole hedge?

To be honest, I'm not sure the brown leaf portions are all that you are dealing with. From what is visible, the entire planting looks stressed and unthrifty. You shouldn't see any signs of twigs or stems with a healthy wax leaf privet....unless pruned up into a tree form. They are typically very dense. And the coloring is a bit anemic as well.

When you say they receive "enough water", what do you mean? How much and how often?

Hi gardengal,

There are three plants affected in the hedge (of about 35 plants total). Several of the other plants had problems with fungus (Chodrostereum and Phytophthora) so we have been treating the hedge with RootShield Plus. However, the other plants that had problems had yellowing leaves. This seems different, with the distinct brown part. The hedge is on a drip system and gets watered once a week when it is dry. During the winter we get some additional rain, but the rest of the hedge seems healthy. I can send pictures tomorrow.

Here are some more photos of the hedge. You can see the three badly affected plants (I cut away a lot of the branches, some were dead, and some had so few leaves) and some of the rest of the hedge. When I was taking photos of the hedge I had a closer look at the healthy plants. I noticed a few brown spots on those as well.

The plants on the left are only a couple of years old, so they are not as developed. The plants on the right are about 15 years old.

Brown spots on healthy plants.

What was the resolution?