When your American Pillar arborvitae is on the decline, there will be several visual signs that you can notice. The most obvious indicator that an American Pillar arborvitae is dying is foliage discoloration. If you see a large portion of your plant's leaves fail to hold a consistent green color, it's likely in distress. Dying American Pillar arborvitae plants may also have brittle bark, broken limbs, and signs of infestations or infections.