Landscape - Dieback in Needled Evergreens II

I recently had a question from a landscaper about dieback in evergreens. This year we are again seeing the loss of many evergreens. The following is the second posting on the subject using material from the Ohio State University.

Each year various narrow-leafed evergreens such as pines, Taxus and spruce are affected with needle yellowing and browning, dieback, poor vigor or death. These are problems often associated with one or more environmental stress factors. An explanation of some of these stress factors follows.

Winter Damage

Evergreen plants transpire or lose water from leaves during winter. If the soil moisture is low or roots are unhealthy, moisture in the needles is not replenished and needles are killed. Again, visible symptoms often do not appear until spring or early summer. Damage often appears on one side or on one branch of the plant, usually the side facing prevailing winds. Needles may turn brown one half or one third of the way from the tips. The extent of browning will be similar on all the needles on the branch.

De-icing Salt Damage

Injury from exposure to de-icing salt can occur on plants. Salt sprayed by traffic on wet roads can cause browned foliage, usually on the side nearest the road. Salt solution runoff also can injure plant roots. Entire plants may die. Needle yellowing and browning often begins at the tips and gets progressively worse. Sometimes soil tests conducted in late winter indicate high salts and confirm the diagnosis.

Herbicide Damage

Injury to evergreens by herbicides is difficult to assess. Symptoms are not always pronounced. Needle distortion may be slight, but root damage could be enough to limit water uptake. Tip damage to new growth is a common symptom with some herbicides. Look for needle distortion and twisting, or needle yellowing or browning, depending on the type of herbicide. On spruce, needle purpling and drop is common.

Air Pollution Damage

When atmospheric conditions allow buildup of smog or air pollutants, narrow yellowed bands may develop on the needles of susceptible plants. In other cases, the tips of the needles may turn brown. Ozone injury to white pine will cause a severe reduction in growth. If this continues for years, it is considered chlorotic dwarf disease. Trees under drought stress may be more prone to damage by air pollutants.

Low Light Needle Drop

Most narrow-leafed evergreens need full sunlight. Low light conditions may result in a slow decline of some evergreens such as junipers or arborvitae. An early symptom is foliage drop in the center of the plant. The condition is common on plants existing in overgrown, old landscapes. Sometimes two plants will grow together. Both will begin to decline. In other cases, a deciduous plant nearby may begin casting a shadow on the evergreen plant during the morning or evening hours.

Transplant or Establishment Problems

Improper planting and poor after-transplant care may result in plant decline several years following transplanting. Common problems associated with planting and establishment include: burlap, especially synthetic burlap, left intact around the root ball; strings or wires left around the trunk; planting a containerized plant without disturbing the root mass; inadequate or inappropriate watering following transplanting; support wires left on the tree too long; setting the tree or shrub deeper than originally grown; and settling following transplanting. These problems are difficult to correct after symptoms have become apparent.

Reprinted from "Yellowing, Dieback and Death of Narrow-Leafed Evergreens" Factsheet HYG-3034-96, by Stephen Nameth, Nancy Taylor, and Jim Chatfield, the Ohio State University Cooperative Extension.