|My Arbor Vitae the leaves are turning brown. I fear that is caused by some kind of mites. What is the remedy?|
|It's difficult to diagnose a problem without being able to inspect the plants. If the browning is on the outside growth as well as the inside foliage, I'd suspect a water stress issue. Droughty conditions can cause foliage browning, but overwatering or poorly draining soils can actually suffocate the roots and the foliage will turn brown as a result. Be sure the soil drains quickly and don't forget to water them deeply once each week.
Spidermites can attack arborvitaes but they typically feed in the center of the plants and cause browning there before they move to the outer foliage. You can check for spidermites by looking for webbing where the foliage meets the stems or by holding a sheet of white paper in the center of the plant and sharply tapping a branch. Debris will fall onto the paper. If little specks begin to move, you'll know your plant has spidermites. Simply hosing the arborvitaes off with a strong stream of water is an efficient way of discouraging spidermites. Spray periodically during the dry months of the year, directing the water towards the inner parts of the plant.
Good luck with your arborvitaes.