When was this planted? Was the leaf loss grandual or kind of sudden. How often do you water?

We planted it 2 years ago. We water less so in the winter (2 times per week and then rainy days, keep the sprinklers off). Did I not water enough? It's also in a shady spot. Could that be another problem?

well they are sun lovers, but some shade would not make all the leaves fall off. did the leaves fall off all at once or gradually over the two years?

You could go out with clippers and take off a small branch and see if it's still alive. There will be a thin green margin just inside the bark if it is alive. If it is brittle and just snaps like a potato chip then the branch is dead. If you have a lot of dead branches the tree is in trouble. Any sign of gophers?

That is a drought-tolerant tree, but it needs a few years to get established and appreciates water when very young. 2X/week in winter should be enough, maybe not quite enough in summer for a young tree. Any pictures of it?

I have the exact same problem as described earlier. Tree was in Oct of 2011. Regular soak for just the tree and sprinklers for ground cover 2x/week. Many of the branches are dead.

Agonis flexuosa is susceptible to phytophtora / root rot...don't know if this is what you're experiencing, though.

That looks like a goner, sorry. :(

If you end up taking it out, inspect the root system and see if it was rotted or dried up. Was it healthy to start with? What size container did you plant it from?

One of mine developed what looked like crown gall so I dug it out. The root system was pitiful.

The other is thriving and growing like a weed--same soil, same amount of water and sun.

Thanks for all the follow up. The tree was healthy, don't know about the root systems though. It was in a 24" box.

A plant autopsy is always useful to find out WHY it did what it did, so you can adjust care if necessary and thereby make failure less likely to happen again whether you plant a tree of the same type, a different tree, or nothing at all.

For example, I dug up several Cercis last year and discovered the roots were all circled in on themselves in the ground--the roots had never spread out correctly for healthy growth. It was not the care they received--they were sitting in their containers far too long and the root systems were doomed. It may have helped in initial planting to have trimmed the roots to remove all the circled material, but that was not done by the installers. The one Cercis I planted myself that was very fresh in a 15 gallon container and that did not have circled roots, was 10 times as healthy, even though it was in the same soil and received the same care as the others.
So I learned to examine the root systems before buying any tree, and after, if they fail, to see what happened.