Updated: May 8, 2019
Ahh friends, no doubt you have seen the sad, spotty browning of these beauties all over East TN. It's likely caused by one of two fungal pathogens (or both simultaneously). The Seiridium canker is typified by elongated, sunken cankers on stems with crusty edges and/or oozing sap. See pic below. The second pathogen is a Botryosphaeria which causes girdling cankers at the base of the dead shoot. These can also produce a dark, cracked appearance on the tissue lining the canker (sunken dark spot or crack-like elongation) don't ooze however.
What to do?!?
The best solution is to replace the trees and have the cut material burned. It's starting to kit other cultivars e.g. Cryptomeria. If you want to keep them as long as possible, the remedy is to change the soil environment for the tree(s). There are no known fungicides to cure the canker(s) but caring for the soil and disciplined, sterile pruning can keep your trees in the landscape for years to come. It all depends on how hard they have been hit and how quickly the soil can be changed.