Question
In April of this year I planted 4 arborvitae in a row, all according to the directions, a couple of them have isolated brown sections, it is a medium brown color, and seems to be entire branches.  The trees are about 6 feet tall and the brown sections are about 5 square inches.  The arborvitae seem otherwise healthy, and only two of the 4 have the problem.  I have trimmed out the spots in hopes that the other branches will fill in around them, what else should I do to save these them?

Answer
Hi there: Your problem could be abiotic IE: too much or too little water. To much sun or transplant shock,or it could be biotic.see below
Arborvitae Diseases
  
Branchlet Death:  The oldest branchlets turn brown in autumn and fall off.Normal browning Branchlets rather than scale leaves are shed in autumn as a normal part of the plant's development.

Kabatina Twig Blight:   Tips of 1-year-old branches die and turn brown or ash-gray. These remain on the shrub for many months. Larger branches can be invaded and girdled. On the dead tissue where it meets the still-living wood, small, black, pimple-like fungal fruiting structures form. Microscopic examination reveals oval, colorless spores. See Phomopsis below.    Prune and destroy infected twigs and branches. It is possible for both Kabatina and Phomopsis twig blight to occur on the same plant. If only Kabatina is present, apply mancozeb to protect foliage.

Pestalotiopsis Tip Blight:  Twig tips turn tan to brown in color and have black, pimple-like fungal fruiting structures dotting their surface. Protect plants from winter injury, drought, and other stresses. Apply copper to protect foliage.

Phomopsis Twig Blight:   Tips of branches die and turn brown or ash-gray. These remain on the shrub for many months. Larger branches can be invaded and girdled. On the dead tissue where it meets the still-living wood, small, black, pimple-like fungal fruiting structures form. Microscopic examination reveals both oval and long, thread-like colorless spores. See Kabatina above.Prune and destroy infected twigs and branches. It is possible for both Kabatina and Phomopsis twig blight to occur on the same plant. If only Phomopsis is present, apply azoxystrobin, thiophanate methyl, or copper when new growth is present.

This is kind of long but I hope it helps your problem,Bill