Question
6 years ago we lined our property with these.  We love them and they are growing well except that we notice several of the lower branches are turning a brown or  rust color.  It scares us to think that it could be a disease that could infect all of them.  Can you advise us please?  
Thank you, Karen in western North Carolina.

Answer
It is most likely an environmental problem with the plants since many of them are showing similar damage.  Plant diseases tend to cause a more uneven pattern where som plants are more severely affected than others.  

I might suggest that you contact your local county extension office since you have a large number of trees.  They will probably ask you to bring a sample (a few affected branches) to their office so they can be examined.  This will be the best way to determine if you need to take any action to save these trees.  

You can find your local office at the following website:
http://www.ces.ncsu.edu/index.php?page=countycenters

Good luck!