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University
of Rhode Island GreenShare Factsheets
Tree
Injuries--Prevention and Care
It has been said that a tree is not planted until it has been
in the ground five years. This reflects the time required
for transplanted trees to re-establish healthy root systems
in the landscape. Proper care and maintenance are required
to keep trees healthy and safe, especially from external
injuries to the tree, which can seriously harm a tree's health.
The best way to care for tree injuries is to prevent them
from happening.
The first and possibly most important steps in injury
prevention are proper selection, placement, and planting of
a new tree. Select trees with well-developed crowns and no
wounds on the trunk or branches. Trees pruned heavily in the
nursery or severely wounded in handling may have serious problems
later. Trees should be planted in shallow, wide holes to allow
rapid root growth after planting. Planting trees too deep is
a common problem. Look at the site carefully and completely.
Is the space large enough to accommodate the mature tree's
crown and roots?
Mulching is an important maintenance practice for trees.
However, an epidemic of over-mulching is plaguing many managed
landscapes. Properly applied mulch increases growth rates,
prevents basal damage, and conserves soil moisture. Organic
mulch such as wood chips or bark should be applied around the
tree to a depth of two to four inches. Mulch should be spread
a foot or more from the base of the tree in all directions,
but never to a depth of more than two to four inches. Mulch
can be placed directly on grass when mulching established trees.
Monitor mulched areas during the winter to detect any rodent
activity. Mulch should be renewed as needed to keep a constant
layer around the tree. Avoid using rocks or plastic sheeting
to protect the tree--rocks cause soil compaction, and plastic
sheeting suffocates root systems.
Woven weed barrier fabric can be effective at reducing
weed competition, allowing moisture and oxygen to enter the
soil around the tree. It does not, however, add organic matter
to the soil or reduce compaction like a natural mulch.
Moisture is critical to trees, but too much moisture
can cause serious damage. Newly planted trees should be watered
once per week (1 inch) in the absence of rain. Established
trees should receive 1 inch of water every 10 to 14 days. These
amounts are in addition to the water a surrounding grass lawn
would need. A new tree in competition with a surrounding grass
lawn may need 2 inches or more of water a week to thrive.
Daily watering causes a lack of soil oxygen, smothering
roots. It can reduce the number of deep roots. Larger amounts
of water should be applied once or twice a week instead.
Water with a hose or coarse-droplet sprinkler at a rate
low enough to keep water from running off. Most tree roots
are not very deep (within the upper 6 to 12 inches of soil),
and deep roots will receive water if enough is applied to the
soil surface.
Fertilize trees only when necessary. If growth is adequate
and steady, foliage appears healthy and there has been no major
disturbance around the tree, no fertilization is needed.
When fertilizing is necessary, slow release, balanced,
granular fertilizer or soil-applied liquids should be distributed
over the tree's entire root zone. Applying fertilizer through
holes augered into the soil or with fertilizer spikes is not
recommended. Routine trunk injections of fertilizers into healthy
trees are not recommended.
Every tree has different pruning requirements. Here are
some important considerations in minimizing tree damage when
pruning or dealing with wounds.
Natural Target Pruning: When
pruning trees, it is important to make final cuts at the
proper location. Cuts
should be made from just outside the branch bark ridge (readily
visible on most species) to just outside the swollen branch
base or branch collar. A cut between these "natural target" points
removes all branch tissue but does not cut into trunk wood.
Leaving stubs leads to unwanted sprouting and decay of
the remaining stem tissue. Cuts made too close (flush cuts)
leave much larger wounds than proper cuts and can cause dieback
of the surrounding cambium. As a result, flush cut wounds do
not heal properly, causing major damage to the trunk from which
the tree may not recover.
Avoid over-pruning trees. Prune lightly once a year for
several years rather than heavily all at once. A good rule-of-thumb
is to prune off no more than about 25 percent of a tree's foliage
in one year. Also try to avoid having to prune branches that
are over one to two inches in diameter. Tipping branches usually
causes more problems later on--it is better to remove entire
branches back to the trunk.
Pruning branches when they are small makes smaller wounds
that close quickly. When branches die, they should be pruned
back to the nearest live branch, and no stub should be left.
Take care not to injure the branch collar or any callus that
may have formed since the branch died.
Maintenance Pruning: Trees
should not be pruned unless there is good reason for pruning.
Reasons may include
safety, removal of dead or injured branches, correction of
a structural defect, or interference with utility lines. Removal
of healthy branches to "thin" a crown or for similar reasons
is never necessary. Topping trees or stripping live branches
from inside a tree are dangerous practices that can severely
impair tree health and longevity.
CODIT -- Compartmentalization Of Decay In Trees
-- is a concept used to describe the reactions that take place
in a tree in response to wounding. When a tree is wounded,
it sets up defensive walls against the invasion of decay fungi
and other microorganisms. The vessels near the wound are plugged
with gums, resins and chemicals that resist the spread of decay.
The living tissues outside the wounded area then begin to form
a callus layer in an attempt to close the wound. A properly
made cut results in a doughnut-like ring of callus forming
all the way around the wound. Wound closure for small wounds
may take only a few months. Larger wounds may take years to
close, or may not close at all.
Use of Mowers and Other Yard Equipment: Trees
often are wounded by careless use of yard equipment like mowers,
weed whips, and other trimming equipment. These injuries cut
through important vascular tissue just inside the bark, which
can lead to decay and ultimately death of the tree. A bed of
natural mulch around the tree eliminates the need to trim or
mow close to the tree's base. Extreme care should be taken
when digging up or tilling the soil under a tree. Many large
and small roots will be cut by such digging, especially if
it occurs close to the trunk.
Trenching and Excessive Change in Soil Grade: Trenching
next to trees cuts major roots. Where possible, tunneling should
be used to leave the upper 18 inches of soil undisturbed. When
tree roots must be cut they should be cut cleanly. Ripping
or tearing tree roots with a backhoe or other implement leaves
large open wounds or may shatter roots, preventing the formation
of new roots.
Changes in soil grade can seriously injure trees. About
90 percent of the tree's root system lies within the upper
18 inches of the soil. Covering tree roots with as little as
3 inches of soil can cause damage by suffocating roots. Filled
areas should be properly tiled and graveled to allow for air
movement and drainage.
Animal Damage: Animals can cause wounds, especially
on smaller trees. Field mice (voles), rabbits, squirrels and
deer commonly feed on the young bark of trees during the winter
when food sources are scarce. Animal damage can be prevented
by excluding the animals from the area around the tree. This
can be done with a simple wire fence around the tree or yard.
Discourage rodents by using a plastic tree guard around the
trunk. Check yearly to ensure that the guard is not girdling
the trunk.
Insect Damage: Insects can cause several types
of wounds to trees--some bore directly into the main stem and
branches, others feed on young shoots and leaves. Inspect trees
regularly for signs of insect damage. When damage is noted,
take care to identify the problem properly and use appropriate
controls.
Cavities and Drainage Tubes: Cavities in trees
require only minimal care. Clean out any loose wood or debris.
Check the cavity for carpenter ants or termites. These insects
should be controlled as necessary.
Do not fill the cavity, but rather allow it to remain
open. Do not scrape the inside of a cavity to remove dead wood.
This may expose live tissue and re-wound the tree, allowing
decay to spread.
Drainage tubes should not be used in trees. Drilling holes
to drain water from interior cavities opens a path for new
decay.
Wounds: Wound treatment
should be confined to removal of loose bark or wood. Leave
the wound exposed so the tree
may begin the natural process of callus formation and healing
or sealing over. "Scribing" a wound in an elliptical shape
once was recommended to help water and nutrients flow around
the wounded area. This is no longer recommended since it only
makes wounds larger and does not improve sap flow.
Wound Dressings: Wound dressings are not recommended
for any tree wounds. Wound dressings actually have been found
to increase decay. Wounds should be left exposed to the open
air to seal naturally.
Injections and Implants: Some insects, diseases
and nutrient deficiencies can be controlled through the use
of chemical injections or implants. These measures, however,
require drilling holes into the trunk and should be used only
after all other available treatments have been considered.
Since injection holes are wounds, they should be made in accordance
with manufacturers' recommendations to minimize the damage
they cause. Injection holes should be kept as small and as
shallow as possible and injection should not be repeated more
than once every two or three years, except in severe cases.
Injection points should not be filled or treated with
wound dressing after treatment.
Cabling and Bracing: Trees that have severe structural
defects or that have suffered serious damage sometimes can
be saved by cable and bracing techniques. In all cases cable
and bracing should be done by a professional arborist who is
familiar with this technique. Not only can improper cabling
or bracing result in damage to the tree, it can also be very
dangerous.
Hazard Identification: Trees that have large, dead
branches or show signs of interior decay should be inspected
by a professional forester or arborist. These trees can become
major liabilities if left standing. Accidents can often be
prevented through proper pruning. Tree work can be dangerous,
and many tasks should be left to professional arborists.
Adapted from Dave Mooter
and Mike Kuhns, Nebraska 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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