Question
Hello,
Three years age I planted 15 arborvitae ( in 5 groups of 3) accross the back of our property and all have done well until this spring when we noticed that two of these groups are brown. \\What is the mortality of arborvitae and would you expect to see them die-off after 3 years. I can send a picture if you need.

Your help in this matter is appreciated

Answer
Dear Wes, After some research, I think I know what the problem is with your arborvitae.  First let me start by emphasizing that arborvitae do best in zones 6-9 which would include most southern  states.  They require good drainage and full sun, so first make sure that you don't have any poorly drained areas where the arborvitae are situated.  If that were the case, you should try to aerate the soil, install a french drain, or somehow improve the drainage.  That being said, I would find that unlikely since they have done well until now.  These plants are very long lived; I have seen them growing by houses that have fallen down from age.  There are a few pests that they are prone to.  One is bagworms (not a big deal in my book, when they get numerous, I just pull them all off).  Next you have spider mites, which you can find by holding a small branch over a white sheet of paper and tapping it sharply.  If anything that falls off moves, then you have spider mites and you should spray with Kelthane if you can find it, otherwise use a product that is effective against spider mites.  The most likely culprit, however, would be a disease called juniper blight which will cause the browning of the branches.  Here's what you will need to do.  First, prune the dead branches off when the plant is dry, disinfecting your pruner with a mixture of 1 part bleach to 9 parts water.  Remove the dead branches from the area completely.  Then you will need to spray for the fungus, using a chemical product that contains at least one of the following:  copper, potassium bicarbonate, or propiconazole.  You will need to spray several times to effectively manage the disease, but you will probably be successful.  Good luck and let me know if you need additional help.  Melissa