In June of this year, planted 5, 15-gallon prunus caroliniana trees. All have robust green leaves on them. However, two of the five trees are completely brown and no leaves on about top six inches of the uppermost lateral branch. They appear to be dying from the top down, even though rest of leaves are very healthy and green. I would love not to lose these trees!

This reply comes from many states away, yet it very much sounds like an water/establishment issue. those leaves and branches at the very top are the farthest way from water and are most vulnerable. If field grown and dug, those two may have a lessor root system than the other 3. if container grown, could be a structural concern with the root system that is now showing up having been planted permanently. if ;there is a warranty involved, contact the retailer. Be sure when you are watering them that sufficient water is being applied for the size of your trees. Contact your local Extension office for a more local and focused reply.