It is possible that an extremely cold winter could cause some dieback. Cedars are not as cold hardy as many conifers and are only marginally winter-safe in USDA zone 6. If you noticed this problem in late winter, it is also possible that salt laid down on roads or paths in winter was plowed, shoveled or simply drifted into your root system. Heavy salt in soil is toxic to most plants. Salt exposure will take its toll and will become noticeable in late winter to early spring.

To test whether the affected branches are really dead, gently scrape at the bark near the end of the branch. Green means alive; brown means dead. If a branch is dead, it is best to cut it off where it meets the trunk, for the sake of the tree's symmetry.

- Courtesy of NYBG Plant Information Service