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University
of Rhode Island GreenShare Factsheets
Needle
Fall, Yellowing & Dieback of Evergreens
Each
year various narrow-leafed evergreens such as pine, yew 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 such as dry soil, wet soil, winter or salt damage.
Excessive
amounts of water can result in a saturated soil, reducing oxygen
levels in the root zone 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 yew (Taxus) planted in a heavy
soil with poor 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 arrives and
stresses the plant. Some evergreens appear to lose vigor and die
back after 15 to 20 years--often 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 also can cause roots on older plants to die
back. The
lack of water for long periods may result in symptoms similar to
those caused by excess water. Soils can pull away from 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.
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. Injury
from exposure to de-icing salt can occur is often evident on evergreens.
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, even killing entire plants. Needle yellowing
and browning often begins at the tips and progressively worsens.
A soil test conducted in late winter can confirm high salt content
in the soil. Injury
to evergreens by herbicides can be difficult to assess, as symptoms
are not always pronounced. While needle distortion may be slight,
for example, root damage could be sufficient to limit water uptake.
Tip damage to new growth is a common symptom of 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. 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. Most
narrow-leafed evergreens need full sunlight. Low light conditions
may result in a slow decline of some evergreens, particularly 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, and 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.
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; settling following transplanting;
and overmulching. These problems are difficult to correct after
symptoms have become apparent.
It is difficult to develop a control program to manage all potential
environmental stresses, but use the following suggestions as a guide
to trouble-shoot evergreen decline. • A wet soil
suggests need for a better drainage system, or simply that
less watering is required. • A dry soil
indicates the need for a better and more uniform watering program,
or the use of an effective mulch. • Mulching, proper
watering, use of a wind barrier and spraying with an antidesiccant
in late fall can all help to lessen winter damage.
Avoid using more than 3 inches of mulch (see GreenShare Factsheet
on over-mulching), and avoid contact
with the tree trunk. • 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. Adapted
from Stephen Nameth, Nancy Taylor and Jim Chatfield, Ohio State
University Extension, 2000
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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