Insect and Disease Fact Sheet Compliments of
New Century 
1-877-79TREES
Yellowing Dieback and Death of Narrow Leafed Evergreens
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.
|
Wet Soil Excessive
amounts of water can result in a saturated soil, reducing oxygen levels to a
point where small
roots weaken or die. This root decline can be sudden or gradual and the:
roots may be invaded by various soil-borne fungi. Continuous wet conditions
lead to progressively worse situations. If the top of the plant is unable to
obtain the necessary water and nutrients, it declines or dies. However, the
evidence of death (needle browning) often occurs at a much later date. An
example is Taxus, or yew, planted in a heavy clay
sub-soil with no sub-surface drainage. In fall, winter and spring, water
accumulates and literally drowns the roots. The tops of the plant may not
succumb until the following spring or summer, when hot weather first arrives
and stresses the plant. Some evergreens appear to lose vigor and dieback
after 15 to 20 years. This often is the result of injury to the root system
from moisture stresses. Heavy soils may limit development of the root system;
root damage easily upsets the top-to-root ratio. .Dieback and poor growth are
often evident. Changes in sub-soil drainage caused by construction will often
cause roots on older plants to die back. |
White pine planted in a poorly
drained wet site. |
|
Drought or Dry Soil The
lack of water for long periods may result in symptoms similar to those caused
by excess water. Clay soils often pull away from the roots as they dry,
drying or breaking the fine roots. Drought stress may be especially
noticeable in the summer on evergreens planted on well drained sites (sand or
gravel), or where roots are
in the top layers of heavy compacted soil. Excessive needle drop and poor
vigor are often evident as a result of drought stress. |
|
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.
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.
|
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. 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. |
Road salt damage on white pine. |
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.
Managing Environmental Stresses
It is
difficult to develop a control program for environmental stresses. A wet soil
suggests need for a better drainage system or that less watering is required. A
dry soil indicates the need for a better and more uniform watering program or
using effective mulch. Mulching, proper watering, use of a wind barrier or
spraying with an anti-desiccant in late fall helps lessen winter damage.
Vertical mulching or core aerating will improve landscape soils. It will hasten
drainage of excessive water, preserve necessary aeration during wet periods,
allow sub-soil water penetration during dry periods and promote the formation
of fine feeder roots. Drill 1 or 2-inch wide, 18-inch deep holes in the soil on
12 to 20 inch centers under affected trees. Fill holes with a mixture of equal
parts of peat and a coarse aggregate, such as pumice or calcined
(baked) clay particles. Control de-icing salt damage by re-directing runoff
water, installing splash or spray guards or by using tolerant plants in injury
prone locations.
Information obtained through the Ohio State Extension Factsheet HYG-3034-96
Insect and Disease Fact Sheet Compliments of
New Century
1-877-79TREES