Tree Health Problems Related to Environmental Stress
Many health problems for trees are related to environmental stress. Hot/cold temperatures,
drying winds, poor soil-root relationships and man can cause direct damage to leaves,
bark and roots, which predisposes the tree to secondary insect and disease attacks.
Maintaining your trees in good vigor through proper maintenance will prevent many
problems, including those listed below.
Prolonged periods of time without moisture, accompanied by drying winds, create
a physiological imbalance in trees. Moisture is lost through transpiration faster
than the roots can supply it to the leaves, resulting in the drying out and death
of living tissue in leaves and areas of succulent growth. This is indicated through
uniform yellowing or browning of the leaf edge. Extended periods of drought may
result in the premature loss of leaves.
When trees enter the winter under drought conditions or with low food reserves,
they are especially susceptible to injury. Winter injury occurs most often when
the frozen soil prevents water uptake by tree roots. In areas where it is very cold
and windy, the tree has to compensate for loss of water from the area of the tree
above the ground. Drought damage and winter injury can be reduced by regular watering
during prolonged dry periods, mulching, and protection from prevailing winds.
Sun scald is a common problem occurring when the tree is young and the bark is thin
and smooth. On winter days, the bark on the south or southwest side of the tree
is warmed to above freezing by the sun’s rays. When the temperature drops below
freezing at night, the warmed tissue is killed. This results in the formation of
a long, narrow canker (or dead spot) on the tree, providing the perfect site for
a secondary attack by insects or disease. To reflect the sun’s rays, paint the trunks
of young trees with white latex paint or use our white plastic tree guards.
Very cold, subzero temperatures can single-handedly kill dormant trees. While cold
weather damage cannot be avoided, the best way to minimize it is to have well-established,
healthy trees before the onset of the first winter. A sudden sharp drop in temperature
can cause differential contraction between the outer wood and interior of softwood
and/or hardwood trees. This results in the formation of a long vertical crack in
the trunk known as a "frost crack."
Trees that have the following symptoms are often in poor health due to root problems:
- Poor vigor
- Off-colored, sparse or prematurely shed foliage
- Extremely slow growth
- Slow decline in vigor and eventual death over three to 10 years
The slow decline in the health of a tree occurs because it doesn’t have the root
surface area to intake the moisture and nutrients needed to meet the tree’s growth
requirements. The tree slowly starves to death due to its inadequate root
system. Restriction of root growth may be caused by improper planting techniques;
poor soil texture such as heavy day; girdling roots; or planting done in hard, compacted
Soil PH Problems
In areas where the PH of a soil exceeds 6.5 (alkali soils), iron is tied up in the
soil and unavailable to the trees. Lack of this essential tree nutrient results
in partial or complete yellowing of the leaves (chlorosis). In severe cases, it
causes browning and/or shedding of leaves.
Resolving iron deficiency problems can be accomplished by:
- applying a fertilizer with high sulfur-iron concentrations
- injecting trees with a solution of iron salts or
- spraying tree foliage with a solution of ferrous sulphate
Herbicide applications can drift in the air and translocate through the soil, injuring
nearby trees. Leaves damaged by herbicides will characteristically cut upward. They
may also have distorted growth, turn brown on the margins and drop from their branches.
If exposure is severe, whole branch shoots will drop, twist and become deformed.
Herbicide damage in trees is typically associated with the use of chemicals for
weed control. Although these trees can survive such damage, the typically lose all
foliage and growth may be stunted. If you notice damage, the best solution is to
cut the tree down to 4 inches above the ground. It will generally reshoot again,
provided the damage is noticed soon enough. Repeated exposure will kill the tree.
Remember that the roots may extend out into the soil two to three times the height
of the tree. This means that although there may not be a tree close to where the
herbicide was used, tree roots probably exist.
Mechanical injuries are wounds to the cambium, bark or roots of the trees. These
wounds expose healthy living tissue to infection by disease organisms or attack
by insects. The majority of mechanical injuries are caused by man. The careless
use of lawn mowers and weed whips around a tree’s base destroys the inner bark and
girdles of the tree. It not only weakens it, but also makes it more susceptible
to attack by insects and disease.
Insect and disease problems in trees are often influenced by environmental stress.
Under normal conditions, trees can resist insect attacks and disease infection.
The effects of drought, soil-root problems or mechanical injury may weaken your
trees and predispose them to attack or infection. In many cases, the primary health
problem for trees is some type of environmental stress, while insects and disease
are secondary problems. Many of these problems can be avoided by keeping your trees
in the best possible health and growing vigorously.