Answer: Unfortunately, based on your description, I am not certain what is happening to your arborvitaes. They should be a uniform green with the exception of some possible browning at the interior along the trunk. (These do normally drop a certain amount of foliage from the interior of the plant each fall.) Browning on the exterior or branch tips could be a sign of drought stess or a pest such as spruce spider mites or a fungal disease, for example. I would suggest you work with your local Cornell cooperative extension to obtain a specific diagnosis, and based on knowing that, determine how to proceed. If a chemical control is needed, they will have the most up to date information on what to use and how/when to use it for maximum results.
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