Answer: One of the features of this variety of arborvitae is that it retains a good green coloration through the winter, so although a slight color change might be seen it would not be browning like you are describing. Evergreens will periodically shed a portion of their very oldest foliage but whenever there is something unusual it is a good idea to look into it. With arborvitae there are pests such as mites which can cause browning in fall (these can be treated with insecticidal soap during the growing season or with light horticultural oil during the dormant season) and also some fairly severe diseases which can cause browning. Over watering could also cause browning. (Although arborvitaes do well with a moist soil, once the fall season arrives with cooler temperatures your watering will be less frequent since the soil stays moister longer naturally in cooler weather.) For this reason I would suggest you consult with your local county extension for a specific diagnosis and suggestions as to what to do -- if anything. They will also have the most up to date pest control recommendations for your area, should that be necessary. Good luck with your shrubs.
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