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Index : Plant Problems - Cultural
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- 5. Treating Cavities in Trees - Top
- Many trees develop cavities as a result of decay. The decay most often occurs as a result of a wound or wounds to the outer bark. Storm damage, heavy power-line clearing, incorrect pruning, woodpecker damage, and construction equipment or lawn mower damage are common causes.
As rot develops from the wounded area, the rot may proceed from the outer portion of the trunk all the way down and into the heartwood of the tree. This can cause significantly weakening and make the tree prone to blowing over, especially in strong winds.
If a large wound has occurred on the trunk, and you suspect major decay has set in, I recommend having the tree inspected by a certified arborist. They are capable of evaluating not only the health of the tree, but more importantly, it’s safety. If the rot involves a major portion of the trunk, then chances are the tree will have to be removed.
If a small cavity has developed, clean out any dead or decayed wood by using a machete, sharp knife or chisel. Cut away any loose bark around the opening of the cavity. This will help speed the formation of healing callus around the opening.
Do not fill the cavity with concrete, foam insulation or any other fill materials. Anything you use to fill the cavity will, over time, shrink and leave a small gap around the inside edges trapping water or creating a haven for insects. Also, do not apply pruning paint or wound dressing to the inner walls of the cavity. The paint will also shrink and crack, leaving areas for moisture to be trapped.
Leave the cavity open to the air. If the cavity is configured such that it traps and holds water, then drill an upward-slanting drainage hole (one-half inch diameter) from the outside to the bottom of the cavity. This hole will allow water to drain out of the cavity.
Do not drill a drainage hole in Saguaro cacti. Such a wound may give rise to bacterial rot. Holes made in Saguaro, commonly made by the Gila woodpecker, will callus over inside and are not endanger of rotting. These callused pockets are referred to as cactus boots.
To prevent rot from developing and cavities from forming, be sure when pruning branches off of a tree, do it the right way. If the limb to be removed is a large and or heavy one, anything bigger 2 inches in diameter, use the three-cut method. This will prevent the branch from breaking away uncontrolled and tearing the bark down and off the main trunk as it does.
Using the three-cut method, first make a pruning cut on the underside of the branch a few inches away from the trunk. Next, move a short distance farther out from the first cut and make a second cut on the top side of the branch. As you cut down through the branch it will break off cleanly at the first cut. The third cut is then made close to the trunk at what is called the “branch-bark collar. The collar is a slightly swollen ring around the base of the branch. Make this final cut at the outer edge of the branch-bark collar.
Pruning cuts should be made with a rough-cut pruning saw. These saws are used to remove any branches larger than an inch in diameter.
I do not recommend home gardeners prune branches higher into the tree than can be reached by standing on the ground. Pruning from ladders or climbing is dangerous and should only be done by a skilled professional arborist. Pole saws, however, can be used to extend your reach from the ground to some branches higher in the tree. But again, use the three-cut method when removing these limbs.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: September 12, 2004
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