Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
How to Care for Tree Wounds
One of
the most common types of tree disease is wound or trunk decay. Decay in a tree
can result in dangerously weak trees, unsightly trees, or in shortening the
life of the tree. Decay in a tree cannot be cured. Proper tree care can,
however, prevent decay or greatly limit the progress of decay in the tree.
Decay
is a condition that results from the digestion of wood by fungi and other
microbes. Wounds through the bark start the processes that lead to decay.
Wounds that expose the wood can be caused by animals, insects, birds, fire,
storms, breezes, and the activities of humans, such as pruning. Of course, not
all wounds lead to decay. Proper care of tree wounds can lessen the chance that
decay will result.
When a
tree is wounded, a natural-process begins that results
in the covering of the wound by bark and new wood. This is called wound
closure, “callusing over” or “wound healing.” Natural processes also begin that
make wood beneath the wound unsuitable for growth of decay organisms. Proper
treatment of wounds can hasten both of these processes.
Proper
care of tree wounds begins with practices that promote callusing growth. Recent
research work has shown that when a tree produces callus rapidly, the extent of
the natural discoloration of the wood in the trunk above and below a wound is less
than when callusing is poor. This is important because decay takes place only
in discolored wood. Rapid callus production commonly occurs in the spring when
trees are growing vigorously. Thus, to reduce decay hazard, the best time to
make large pruning wounds is from the time that buds start to swell until the
leaves are nearly fully expanded. This is usually in March, April, or May for much
of Ohio. The sort of large wounds we are referring to are those involving
branches larger than 1 ˝ inches in diameter.
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Figure 1. Trim branches without collars flush to the
trunk |
Figure 2. Trim branches with collars or other natural
projections at the collar edge. |
In the
past it has been recommended that the bark around ragged wounds on the trunk or
large branches be trimmed away from the wound in an elliptical form, with the greatest
dimension of the ellipse above and below the wound. Recent research suggests
that when wounds are made in the spring (as recommended above) this is not a good
practice. This is because trimming away healthy bark may lead to increased wood
discoloration and hence to increased decay. Elliptical trimming may not be important
when wounds occur in late summer or fall either. The bark over these sorts of wounds tends to
die and become loose in an elliptical fashion naturally.
Healing
associated with branch stubs may often be delayed and lead to increased decay
within the tree if the stub is not properly pruned off. Cutting flush with the
tree is generally best (Figure 1). Some branches have collars;
"shoulders" or other natural projections. These should not be trimmed
off (Figure 2). When natural projections or
collars are removed, not only is there a larger area to be callused
over, but chances of decay organisms entering the wound and, becoming
established are greater. Branch stubs previously incorrectly pruned should be
corrected as promptly as possible. Care should be taken, however; not to cut
into the new callus tissue that has begun to form in response to the wound.
Try to
keep wounded trees growing vigorously. This will increase the rate of wound
closure and reduce the amount of discolored wood and decay associated with
wounds. Trees should be fertilized properly and watered during droughts. Aerate
the soil if it is compacted. Do not plant trees that will grow to be large too
close to a house, paved area, or other
restrictive object or soil, situation: Thin out less valuable, competing trees.
Take measures to control debilitating
insect infestations. Protect the tree from wounds made by careless mowing or
weeding practices. Prune badly broken branches promptly. You may use wound dressings
if you wish; however, some tree care specialists feel that wound dressings
interfere with healing or callusing.
Trees
in the urban landscape must be helped. Early in the life of the tree establish sound
maintenance programs for all trees. Part of such maintenance is the prevention wounds,
maintenance of tree vigor, and proper wound care.
Information obtained through the Ohio State Extension Factsheet HYG-3045_96
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES