If during hot summer months there is little rainfall, an arborvitae tree can turn brown due to drought stress and sun scorch. Deep watering of the soil around the tree is a solution to this problem. There are many other possible causes for arborvitaes to turn brown during different seasons of the year.
In winter months, arborvitae tree leaves can turn brown due to freeze injury and winter burn. Another sign of this problem is splitting of the trunk near the bottom of the tree. The sun, harsh wind and little water are factors that cause this problem. One can combat this problem by wrapping the tree in burlap.
Mites, aphids and boring insects also damage arborvitae trees by causing brown spots on leaves. Likewise, root rot and other fungal diseases also can cause brown spots on leaves and branch tips.
Some other possible factors that also can cause this problem on arborvitae trees are using too much nitrogen fertilizer and dogs urinating near a tree.
An arborvitae is an evergreen tree or shrub belonging to the Cypress family. There are different species of arborvitae, including the Green Emerald arborvitae. Arborvitae trees are hardy and can live up to 50 years with the proper care.