Clemson Extension Forestry and Wildlife

Tree Issues: From Conks to Cavities to Decay

Winter is rapidly approaching and as the autumn leaves fall, we begin to get a better glimpse of tree trunks and branches. Now is a great time to assess your trees and plan your winter pruning projects or perhaps even tree removals. December through mid-March is the best time to prune trees in our area as they are dormant, won’t “bleed” much, are less likely to attract undesirable insects, and are less likely to suffer from diseases. So exactly what should you be looking for? Well, let’s start with the easiest and most obvious.

Your tree may have suffered storm damage over the summer, and some larger limbs may have broken off halfway from the trunk. The broken half may even be dangling dangerously, waiting to drop at any given moment. All dead, broken and damaged limbs should be pruned out or back accordingly.

For large trees with forked tops, look for staining around the base of the fork. Is the fork holding it water? Have you noticed the fork starting to split? If it were to split, is there a target, say a home or a car to hit? Some forked trees are good candidates for cabling or bracing. This helps recenter the weight of the tree.

white mushrooms growing on the main stem of a tree
Mushrooms or conks (pictured) on branches, trunks, or at the base of the tree indicate advanced decay and a high probability of tree failure.
Photo credit: R. F. Polomski, ©2021 HGIC, Clemson Extension.

Next on the list are tree cavities. Do you see any sunken areas or hollow cavities on the trunk or larger branches? How large is the cavity and where is it located? If you find a cavity on your tree, you can assume there is an area of decay surrounding it, whether you are able to see it or not. So, there are several things to consider at this point. Wherever the cavity is along the trunk, it has created a structural weakness at that point. If we were to have strong winds and the tree was going to “fail”, it would most likely happen at this location. So, how much weight is there above the cavity? Huge large, heavy branches? More importantly, if the tree were to fall, is it within striking distance of a home, garage, boat, cars, or even a child’s playground?

Another basic assessment you can do is to see how deep the cavity is. Find a large metal rod or long screwdriver and see how deeply you can poke into the cavity. Is the wood spongy and soft? Then the level of decay is probably quite significant. If the rod is able to go halfway into the tree, then you know it has rotted halfway through and only half of the tree is supporting the massive weight above.

One test I conduct regularly is to sound out the area with a hammer or mallet. This is a simple test and can be conducted by knocking around the entire tree, from the ground level to as high as you can reach and listening for a hollow resonating sound. You will know it when you hear it, trust me. Hollow sounds indicate extreme decay and significant loss of structural support.

To finish up the tree cavity assessment, perhaps the easiest sign of significant decay will be seeing conks located on the trunk of the tree. Conks, also called bracket fungus, are basically large hard shelf-like mushrooms growing on the trunk of a tree. If you find them growing closer to the base, it could be an indication of root rot.

One thing you should not do to tree cavities is fill them. Filling a cavity with foam or concrete will not stop the decay and it will not provide additional support. The same goes for pruning. We no longer recommend sealing pruning cuts. Correct pruning cuts will allow your tree to heal naturally and stay healthy.

In closing, I cannot stress enough the location of a hazard tree to a target, a target being people or property. If you have a tree with a structural defect in the trunk within striking distance of people or property, then you should strongly consider having it removed. We all love our trees but they are not worth the destruction of property or most importantly lives.


Carolyn Dawson, Cooperative Extension, Forestry and Wildlife Agent

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