Originally posted by Mike Maas
What is the advantage of removing decayed wood from inside a cavity?
1. Removes habitat for woodboring insects such as carpenerworms.
2. Makes less favorable conditions for fungal and other decay organisms.
3. Allows a noninvasive assessment of cavity size and strength loss to be made.
4. Makes oodles of easy money for unscrupulous snake oil salesmen.
Three of the above answers are correct. You can pick the wrong one, according to your prejudices, beliefs and ability to reason.
The following 3 paragraphs, from an upcoming article in TCI, also might answer your question, Mike.
Many insects that are harmless to the living tree—ants, termites, centipedes, sowbugs, for instance—can be found under the dead bark, but there is no reason to go after them. However carpenterworms, Prionoxystus sp., are also active in these infection sites. As Johnson and Lyons report in Insects that Feed on Trees and Shrubs, “Over a period of time the activities of the carpenterworm larvae may prove disastrous to the host tree…” The need to expose and treat this pest calls for the removal of dead bark. Bacterial activity and slime flux on older oaks can and does kill cambium, expanding the diseased area every year. So there is also a clear need for noninvasive methods to preserve the tree.
The first job is to find out which portions of the bark are dead. The first cues are visual; lesions bleeding with blackened sap at the margins of the diseased area. These lesions appear very similar to those caused by infections of fungi such as Phytophthora sp. Auditory cues are gained by tapping with a rubber or plastic mallet outside these lesions. A solid sound indicates living bark over solid wood. Tapping inside the lesions will yield a hollow sound, indicating dead bark. A stethoscope can be used to better hear the sound, but is not often necessary to detect dead bark. The next step is probing these areas with a blunt instrument such as a trowel or screwdriver. Remove all discolored bark down to the wood. In some cases this means removing a lot of bark. If the infection encompasses more than half of the trunk and decay is advancing inward, it is doubtful the tree will remain safe for very long. It is probably best to treat these unfortunate trees with a chain saw at ground level.
Cut around the infected trunk or branch until you come close to healthy cambium. Take care not to cut into healthy bark or wood. Excavation of wounds is still viewed with skepticism in some circles precisely because of the fear that careless digging will result in more damage. When most of the dead bark has been removed, a sharper tool will trim the edges of infected material. In Helping Plants Survive Armillaria Root Rot (November 2003 issue of Tree Care Industry), the author describes the excavation of tissue infected with the fungus Armillaria. Because bacterial infections seem less virulent, and do not cause wood decay like Armillaria does, a more cautious approach to tissue removal seems to be warranted. The goal is to come as close as possible to healthy tissue without cutting into it. A blunt-tipped knife, such as a linoleum knife, can trim the last scraps of diseased bark without scratching the wood. There is no need to trace the wound into an oval, because sap can flow laterally within the cambium. Careful removal of dead bark may reveal the cambial layer, still light in color and adhered to the wood. The more living cambium that is left, the sooner the tree can close its wounds. Rinsing off the last of the debris with a sharp stream of water from the garden hose or better yet a jet of air from a pneumatic tool will finish the excavation work.
