Wood rotting fungi usually invade trees through wounds. Wounds offer fungi an avenue into the interior of the trees. They also act as a conduit for the moisture and oxygen that the fungi need to successfully continue their invasion. Pruning and wound treatments are designed to promote rapid healing of wounds, thus minimizing the impacts of the woodrotting fungi.

Why Prune Trees?

The general reasons for pruning shade trees are related to safety, tree health, and tree appearance.


Dead, split, and broken branches are a safety problem. They may be extremely heavy, and thus, if they fall, pose a hazard to human life and property. These branches should be removed as soon as they are found. Low-hanging branches along streets and roads may obscure the vision of automobile drivers and pedestrians. It is often necessary to remove such branches to a height of 10 to 12 feet to prevent accidents. Also remove branches that threaten to interfere with utility lines.


Tree appearance may be affected by pruning. Misshapen trees can be pruned to give a more pleasing appearance. Also, trees may be kept small by judicious pruning of new growth during the summer.

Tree Health

Broken, dead, and diseased branches may affect tree health. Disease causing fungi enter trees through these branches, so it is necessary to remove them. When diseased limbs are removed, the saw or knife should be sterilized in clorox to prevent spread of the disease to other trees. Where a fork occurs, one of the limbs should be removed while the tree is small to prevent future splitting.

When to Prune

It is best to prune while limbs are as small as possible. Try to anticipate pruning needs and remove branches while they are under 2 inches in diameter if possible. The smaller a branch when it is pruned, the more rapid will be the healing process. Trees can be successfully pruned any month of the year. However, some groups of trees, including the maples, walnuts, and birches, "bleed" sap if pruned in the early spring. Although the bleeding causes no appreciable damage to the tree, if the bleeding is objectionable to the tree owner, these tree groups should not be pruned during the spring season.

How to Prune

Figure 1

Determining where to prune a branch is extremely important. There is a swelling on the bottom of each branch where it connects to the trunk. There is also a bark ridge just above each branch where it connects to the trunk. When dealing with small branches, draw an imaginary line from just outside of the top bark ridge to just outside the swelling on the bottom of the branch. Then cut the branch just outside this imaginary line (figure 1, item 3). This will allow the tree to heal over the pruning wound most efficiently.

Larger branches must sometimes be removed from trees. If an attempt is made to remove these branches with a single cut, when they fall, their weight often peels away the bark along the tree stem below the cut. To prevent this, several cuts are needed. First, a cut should be made halfway through the branch and from the underside of the branch a short distance from the trunk. Then the limb should be cut off from above, the upper cut being about 1 inch outside the first cut. Finally, the stub should be cut just outside the bark ridge branch swelling line as previously described. Figure 1 illustrates the proper pruning of a large branch.

Treating Pruning Wounds

In the past, most authorities recommended that the wounds caused by pruning be painted with a wound dressing. Recent research, however, has shown that this is unnecessary, except in areas where oak wilt disease is a problem. For oak wilt occurrence and special treatment recommendations contact your local extension agent or forester.

Figure 2

Wounds on trees should be treated as soon after discovery as possible. First, all dead and loose bark, wood splinters, and ragged edges should be removed (figure 2, item 4). Then the wound should be trimmed to an elliptical shape, pointed at the top and bottom (figure 2, item 5). This shape has been found to be most efficient for eliminating water pockets in the wound and promotes healing. Remove any protruding wood inside the wound and smooth out the wound surface. Again, no wound dressing or paint is needed except in oak wilt areas. The wound will heal with time.


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