Distant objects showing in front of nearby objects

I’m following this tutorial.

The wheat is mapped (albedo and alpha) onto an object that has been imported.

For the most part it’s kind of close. However, as you can see in the shot below, I’m seeing distant foliage through the nearby foliage.

Not sure what’s happening here - any help appreciated.

wheat.jpg

Anyone? Thought I’d have it solved by now but haven’t found a solution.