Why Are My Cedar Trees Turning Brown?

The cedar or Cupressaceae family includes approximately 140 species, which include not only variants of the cedar, such as northern white cedar (Thuja occidentalis, hardy in U.S. Department of Agriculture plant hardiness zones 3 through 8) and eastern red cedar (Juniperus virginiana, USDA zones 2 through 9), but also common junipers (Juniperus communis, USDA zones 3 through 8) and the smaller cousin, the arborvitae bush (Thuja occidentalis L., USDA zones 3 through 7). While some browning is part of the plant's natural life cycle, excessive or year-round browning could be an indicator of disease, infestation or environmental damage.

Life-Cycle Browning

Evergreen is a misleading term. All leaves and needles have a definitive life cycle. The difference is that those of cedars and other conifers, or evergreens, don’t die all at once. Typically, cedars lose the needles closest to the trunk, which are the oldest ones, in late summer or fall. This process lessens the stress on the branches when snow and ice weigh them down in the winter. Look closely at the browning on your cedar to see where it appears on the branch. If it’s on the inside and the needles on the outside edges of the branch are green and healthy, there may be no cause for concern.

Weather Factors

Mother Nature’s temper tantrums can be hard on cedars. Drought or extreme heat and cold can cause some or even all of your cedar’s needles to turn brown. You can’t control temperature extremes, but you can help your cedar by providing extra water during hot or dry periods. Use mulch to help maintain moisture and plant your cedars away from the road to avoid damage from road salt. The good news is that even if your cedar turns completely brown in winter, it may come back in the spring.

Transplant Shock

All plants suffer a setback when their roots are disturbed, so it’s normal to see some browning after you have added a new cedar to your landscape. If the tree becomes increasingly brown over several months, however, it’s possible that it was improperly extracted by the nursery or that you did not properly prepare the soil bed. Be sure to purchase your trees from a reputable nursery that provides a guarantee in case the tree does not survive transplanting.

Bagworm Infestation

Cedar trees are susceptible to the ravages of bagworm caterpillars, whose 1 ½ to 2-inch long cone-shaped dwellings look deceptively like a seedpod. The brown cocoons of the females serve as a winter home for 300 or more eggs that hatch in the spring. The larvae then emerge to feed on the cedar's needles. The infestation stresses the plant, which may cause browning. In large numbers, bagworms can even completely denude a tree. If you notice a small number of such bags, you can remove them by simply pulling them off. A more serious infestation may require the use of a pesticide. Spinosad is a good choice because it is a natural soil bacterium. Mix 2 ounces with 1 gallon of water and spray needle clusters on both sides. Another option is bacillus thuringiensis -- or BT -- that you can buy in concentrate form. Use 2 ounces with 3 gallons of water and spray branches from both sides. Wear protective gear and gloves, and follow all label safety precautions when applying pesticides.

Cedar Quince Rust

Depending on their neighbors, cedar trees can become victims of gymnosporangium clavipes, commonly known as cedar-quince rust. This complicated little organism needs two types of trees to survive: a cedar -- usually a juniper or a red cedar -- and a member of the rosaceae family, which includes primary apple (Malus domestica, hardy in USDA zones 3 through 8) and about 480 other species. The cedar and the other tree pass the fungus back and forth. On the cedar, the fungus lives within the bark and causes swelling that encircles twigs and small branches. Masses of orange or rust-colored spores emerge from these swollen areas in April or May and travel from there to a nearby summer fruit tree host, where it embeds in the fruit, multiplies and rides the wind back to your cedar in the fall. You can easily distinguish this ailment from natural browning because the discoloration occurs towards the end of the branch and lies on top of the needles; it’s not the needles themselves turning brown. For a natural approach to managing this disease, remove affected branches and closely monitor for signs of recurrence. If the problem persists, you can try a fungicide containing the active ingredient myclobutanil. Purchase the 1.55 percent concentrate and mix 1/2 ounce per 1 gallon of water. Wear gloves, protective clothing, and follow safety precautions on the label when mixing and applying. Spray branches and needle clusters from both all sides.

Tip and Twig Blights

Cedars can be affected by tip and twig blights that cause browning of needles, shoot and tip dieback and dropped needles. Problems usually occur when weather conditions are wet and warm. Phomopsis Tip Blight affects newly developed branches and tips that are smaller than a pencil. Older and more mature needles are resistant to the fungus and remain green. The problem mainly occurs during spring or summer when new growth develops. Affected twigs turn pale and then turn to a reddish-brown and eventually turn brown and die.

Cercospora Twig Blight fungus attacks the lower portions of the cedar's inner foliage first and works its way upwards throughout the plant. Though the branch tips remain green and healthy, the inside of affected trees drop all their foliage as it turns brown and dies. The problem generally occurs during late summer. To avoid both blights, plant cedars in well draining locations not located in full shade, allow good air circulation between multiple plantings and do not water from overhead. Prune infected growth back to a healthy section of the plant with disinfected pruning tools. Wipe the blades off with alcohol between cuts. Treat the plants before the infection occurs with a ready-to-use copper fungicide, saturating all portions of the plant. Always follow the particular product's directions for use and wash your hands after using.