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Winter injury occurs in late winter and early spring.
Heavy coatings of ice and snow allowed to remain on trees
and shrubs may cause serious branch breakage.
Control:
In landscape settings, plant trees in a location
protected from buildups of snow and ice or remove the
buildups as they occur. Injury often occurs in
shelterbelts, where little can be done to prevent it.
Alternate freezing and thawing of the soil may result in
damage or death to the roots. To protect against root
killing, water the trees deeply in late fall and during
summer dry periods. The use of a mulch during winter
months is important to conserve root moisture, prevent
deep freezing, and prevent alternate freezing and thawing
of the soil. Popular mulches used are straw (flax straw
is best), bark chips, leaf mold, or well-rotted manure.
These mulches are usually left in place over winter and
either removed or worked into the soil in the spring.
Bark chips may be left on year around.
When this condition is prevalent, tops of large trees
(spruce, pine, etc.) may yellow and die back due to
stressful growing conditions such as overly wet soil,
chemicals in the soil, alkaline spots, drought, etc.
Foliage on the trees begins to thin out and new shoot
growth is stunted.
Control:
Water and fertilize landscape trees to maintain good
vigor, and also mulch and water in late fall. Plant the
trees in well drained, fertile soil and plant adapted
species and varieties. (see Extension Bulletin No. 13,
Trees and Shrubs for North Dakota, for a list of reliable
winter-hardy evergreens). Control insects (see summary).
Make sure that the water used for irrigating the trees
is not so high in sodium or other salts that the water
will do more harm than good. Water quality can be a
serious problem in many parts of the state.
Foliage on the trees appears to be scorched as if by
flame. The needles dry and turn brown from the tip down.
Tips of the branches begin to die back. Injury follows
periods of very hot, dry, windy weather. Severe winter
weather and spider mite injury cause similar symptoms.
This condition is quite common in North Dakota among pine
and spruce trees growing on exposed sites.
The combination of summer drought plus winter drying
causes needles of spruces, especially Colorado spruce, to
turn purplish in late winter and spring (compare
Rhizosphaera needlecast, below).
Control:
Where possible, keep trees well watered during hot, dry
periods. Control spider mites (see summary). Plant only
hardy varieties.
 Sunscald (bark scorch; winter drying; winter
burn)
Two types of sun injury, winter and summer, are found
in North Dakota. Winter sunscald (winter
burn) (73KB color jpg) is
caused by a combination of high and low temperatures
during the late winter or early spring. Temperatures on
exposed surfaces of the shrubs or trees increase
sufficiently to allow respiration in normally dormant
cells. As the cells become active, water is given off.
Because the soil is still frozen and roots are inactive,
moisture in the active cells cannot be replaced. The
result is drying of the tissue. The incidence of injury
is usually much higher following a late snowfall,
especially if followed by sunny weather and warm winds.
Injuries localized on sun-exposed surfaces are classed as
"winter sun scald" (winter burn); this
distinguishes the injury from "sunscorch" which
is due to the drying effect of high summer temperatures.
Winter injury is probably a much more common cause of
leaf drying and limb cankers than summer injury in the
northern regions.
Stages in severity of damage caused by sunscald are:
first the killing of needletips, followed by the death of
the entire needle (56KB color jpg), then killing of buds,
the formation of cankers on small upper branches, and
finally the formation of cankers on large branches which
can kill the tree. Each stage in increased severity
includes all previous stages of damage. Early stages of
winter sunscald are frequently not observed. Following
the period when injury occurs, affected tissues appear
dull or discolored, and there may be some shrinkage due
to drying. Foliage eventually turns
brown (56KB color jpg) and
drops. If branches are killed, the bark loosens from the
wood and the brown, dead portions can be readily peeled
from the underlying wood. This wood may also be
discolored. With severe injuries, the bark soon splits
and cracks. The final result is weathering and peeling of
the bark to produce an open wound. Moderate types of
winter sunscald are confined to small upper branches on
the southwest face of the plant. The very severely
injured trees or shrubs may die later in the season;
those less severely injured will heal and survive.
Injury from road salt (46KB color jpg) may resemble winter
burn. Usually the location is enough to indicate the
association between damage and nearby highways.
Control:
When sunscald occurs frequently, follow practices in home
plantings which prevent excessive overheating of the
sun-exposed surfaces. Board, lath or burlap screens may
be made to shade exposed surfaces. A darkly painted house
does not reflect sun's rays as readily as light colored
siding. Remove all dead branches only after growth starts
in the spring. Many branches with winter burned needles
will put out new shoots (55KB color jpg). Control mites with a
recommended miticide (see summary). Fertilize trees in
the spring to stimulate growth. Keep trees well watered
during dry periods in summer and fall.
For shelterbelt trees, maintain vigorous growth of
trees and control insects or mites. Larger trees do not
require cultivation; avoid cultivation which will damage
roots or branches.
Additional winter burn
photo (54KB color jpg).
Dead, oily foliage is seen near the base of the tree.
The foliage is dark brown to black in color. This
condition appears most often during winter months when
snow covers the tree trunks and urine is deposited on the
foliage. Low and medium shrubs such as Andorra, Pfitzer,
Hetz and Savin junipers and arborvitae are most often
damaged.
Control:
Try one or more commercial "dog off" sprays or
pet repellents. Also protect shrubs with fencing or by
covering with snow or some other type of cover.
Confinement of male animals, when possible, eliminates
the problem.
One of the most common and yet least recognized causes
of tree problems is root disturbance, often associated
with some sort of construction activity such as laying of
pipe or cable, street widening, placing a new building in
an older site or turning residential areas into parking
lots.
Because young trees—and even moderately sized
ones—can be successfully transplanted, people
sometimes think that root damage is of no consequence. An
established tree has a wide, spreading root system. Loss
of a substantial part of this root system will result in
decline of the tree unless corrective measures are taken.
Old or very large trees seldom have sufficient
regenerative capacity to survive major root damage,
although it may take such a tree several years to die.
Home builders or contractors frequently try to preserve
trees by fencing off an area around them. This protects
the trunk from damage but is of little help to the root
system, which extends out well beyond the drip line of
the tree crown. Excavation, even at a distance of 10 feet
from the trunk of a large tree, may destroy 30 percent of
the root system. Nor is major soil disturbance necessary
for substantial injury. Cutting a narrow ditch for laying
utility cable effectively disconnects the entire root
system on that side of the tree.
Changes in grade will also damage tree root systems by
upsetting the balance of air and water the roots need to
survive. Soil compaction from heavy vehicles can kill
roots. When tree roots are damaged by any of these
causes, the tree begins to decline. The first symptoms
may be leaf scorch. Later, twigs and shoots die back,
then whole branches may die. Death of the tree may
follow.
The development of "tree spades" and other
heavy tree moving equipment has allowed nurseries to sell
large specimen trees, particularly spruce and pine. When
these have been grown in a tree nursery where regular
root pruning has been practiced, the results are
successful and the tree becomes established readily on
its new site. All too often, however, specimen trees are
moved from shelterbelts or other plantings where trees
have grown undisturbed for years. Trees on such sites
have diffuse, widely spread roots, most of which are lost
when such a tree is moved, even with a large machine.
Such a tree has a poorer chance to survive, especially if
the new site is exposed to wind or the tree cannot be
adequately irrigated.
Older spruce trees in established plantings often lose
their lower branches, exposing a bare soil area around
the tree. In this area tree roots are very close to the
surface. Controlling weeds in this zone is sometimes a
problem, but cultivating or tilling this area will cause
serious root damage. Even the most shallow of cultivation
in this zone will injure many feeder roots and may
predispose the tree to other problems.
Do not cultivate under spruce trees. If only a few
weeds are present, hoe out or pull by hand. A mulch of
pine needles or other loose organic material will control
weeds and also preserve soil moisture.
Some herbicides are labeled for use in shelterbelts;
each label specifies the restrictions for use and which
tree species are labeled. Weed killers (herbicides) can
be especially damaging to spruce trees. Their shallow
feeder roots make such use risky even with supposedly
"safe" chemicals.
Control:
Protect tree root systems, not just the trunk, during
construction. Prevent heavy equipment or traffic from
travelling near trees. If this is unavoidable, aerate the
soil immediately following such activity. Do not allow
utility trenching near trees. Insist upon written
guarantees by contractors working near valuable trees. If
major root damage to large trees is unavoidable, consider
removing the tree and replanting. Often the savings by
this procedure will more than pay for specimen size
replacements. Do not pave over tree root systems. Roots
need oxygen to live!
If tree roots are damaged, careful pruning to balance
top and roots can sometimes help the tree survive. Get
the help of a professional arborist. Your city or state
forester may recommend someone or offer direct
assistance. Water and fertilize to promote vigorous
growth.
Injury from plowed-up snow.
(59KB color jpg)
Herbicide damage. (51KB color jpg)
B A C K | N E X T | C
O N T E N T S
Pathological Disorders - Foliage Diseases
Pathological Disorders - Shoot
Blights
Pathological Disorders - Branch and
Stem Diseases
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