There are several damaging arborvitae tree diseases and pests. Avoid rot diseases by planting "Emerald Green" arborvitae in well-drained soil and do not overwater. These trees have no serious pest or disease issues, don’t require fertilizer or pruning to … Browning on arborvitae leaves can occur at various times of the year. Root rot, a set of fungal diseases, could be the problem, as they are fairly common with arborvitaes in our area. In these arborvitae diseases, the tips of the tree change its color into ash-gray or brown, which is an indication that they are dead. I have not changed their watering schedule. In most cases, the arborvitae will have pre-existing conditions and diseases before it is infected with pestalotiopsis blight. Due to their ubiquity on the landscape, arborvitae is often maligned as an unremarkable plant. Examination with a hand lens shows that some of the affected needles appear to be hollowed out. This remains on the shrubs for a long time, which in return creates fungal diseases for the tree. Just be sure that the site gets some sun and is large enough to accommodate the tree’s full size. Some of the most common problems are: Bagworm – Bagworm is a type of moth whose caterpillars feed voraciously on arborvitae leaves and twigs. I suspect a fungus and did spray with liquid copper about three weeks ago. One tree is especially bad with large areas brown and dry. Our living fence has a dead tree in it, it is time to pull it out, replant, and figure out what went wrong. A mass of gummy sawdust ("frass") at the base of an injured arborvitae shrub signals the presence of borers, the larvae of the cedar tree borer. Hosts Arborvitae is routinely planted by green industry professionals and homeowners as a landscape ornamental. Cedar Tree Borers ƒ{ In its larval stage, the Cedar Tree Borer bores into the inner bark and wood, frequently girdling the arborvitae, making it more susceptible to heat, drought, and disease. Similar to other blight diseases, pestalotiopsis causes the foliage to discolor, from yellow to dark browns and blacks. My arborvitae are showing signs of disease. These trees are twelve to fifteen feet tall and about twelve years old. When it happens in summer, the color change could be happening because of drought.But if your arborvitae shrub turns brown in winter or early spring, the likely reason is winter burn. Once an arborvitae is established, you don’t need to do much to tend it. When the dead tissue comes in contact with the living tissue, there forms a pimple-like black fungus. Scenario: In an arborvitae planting you find dead needles, either individually or in groups, mixed in with green needles on the same branch. Planted in rows, arborvitae provides dense screening for privacy and border establishment. Arborvitae Diseases, Pests & Signs of Problems. When planted as a specimen tree, they can be a center piece of any landscape. The Reason Why Arborvitae Foliage Turns Brown . Pestalotiopsis blight is a fungal disease that only infects relatively weak and ailing foliage.