Browning of arborvitae can indicate several different conditions. Browning of the inside branches often occurs to shed old limbs to make room for new ones, according to Ohio State University horticulturist Elton M. Smith. These can be removed without harm to the tree. Browning of the tips of branches can occur after a hard winter. These regenerate new growth without difficulty. Low branches near the soil line may turn brown and bark may split where hard freezes expand the moisture around trees. Aphids and spider mites can attack arborvitae trees, damaging foliage and cause large, brown areas. Fungal disease can also attack arborvitae shrubs, causing yellow or brown spots on branch tips that can spread to the inside of the branch causing it to die.