Question
How to Trim a large stump off a silver maple tree? Our silver maple, which is about 60 feet tall, is healthy, according to 3 tree trimmers who have examined it. However, 8 yrs ago an enormous limb broke off about 5 ft off the ground, in an ice storm. A non-expert man with a chain saw trimmed that stump so the cut was parallel to the ground. Over the years, the standing water on the surface rotted it out. When we discovered the rot, we had a different man come and trim off the rot and left it at a severe angle so the rain would run off. He said to paint it with ordinary paint. Which we did. 2 coats. By the end of the following summer, the wood was again rotting near the edges where the rain ran down between the bark and the wood. The rot went about 6-8 inches deep. We chopped it out and then coated the whole stump, which is just over 2 feet in diameter, with black tree sealant- 2 coats. This summer we noticed ant activity in the wood just below the bark, which had rotted again in one spot. There was sawdust and ants and we assume, therefore, carpenter ants (as they had already killed 2 of our neighbor's trees). We put out ant traps and are hoping for the swift removal of the ants. We called another tree trimmer to come and look. He said he would cut the stump back to the join, where it comes out of the main trunk and make it flush with the trunk. Yet another trimmer said that takes it too close to the heart of the tree. The stump surface is now about 5 inches from the trunk. We need professional advice. Should we leave the stump as is and re-seal it again? Should we pull off the bark near the edges where the rain gets in and seal all that inner wood with sealant? Should we let the man cut it off right back to the trunk so it is flush and no stump remains? Please advise how we can save this beautiful silver maple?

Answer
It should be cut off flush with the living trunk so no stump remains. No need to coat or paint the cut with anything. These wound dressing will slow the healing process down.

The carpenter ants should be controlled. Carpenter ants nest in trees in one of two situations: 1) in rotted, decayed wood or 2) in the center heartwood section of the tree. In neither case are they harmful to the tree. Control is unnecessary for the tree's health, as the ants are taking advantage of preexisting soft, weak wood to establish their colony. Insects, disease, or environmental conditions such as drought are often responsible for weakening and killing limbs or sections of trees. This allows wood rot to set in, which results in wood decay, giving carpenter ants the opportunity to colonize the tree. Carpenter ants use knots, cracks, holes, and old insect tunnels to gain access to these areas.

Control of carpenter ants in trees is warranted if there are indications that ants are entering homes from colonies in trees. If there is evidence of this, the best control is to bait the colony.
Baits, such as Terro. Baits tend to be slower-acting than other forms of carpenter ant control, but they are easy to apply and give good results, especially when the nest can't be located. The ants themselves will carry the bait back to the nest, which usually provides colony elimination.

There are a few baits available to nonprofessionals for carpenter ant control. Most retail products are liquid or granular formulations containing hydramethylnon, sulfluramid, abamectin, or boric acid. An inexpensive liquid bait of 1% boric acid in a 10% sugar water solution can be mixed at home, but it is very slow acting and must be constantly replenished. Baits vary a great deal in their effectiveness. Carpenter ants have complex food preferences, and some of the sugar-based baits will not be attractive to the ants long enough to be successful.  

If the nest is exposed  you can use a liquid or aerosol ready-to-use insecticide, such as bifenthrin, cyfluthrin, deltamethrin, or permethrin. Spray the insecticide directly into as much of the nest as possible. The more of the colony that is exposed, the better your chance of destroying it. It is necessary to anticipate a carpenter ant colony and have a product ready at the start of construction. Once the nest is exposed, that portion of the colony will try to relocate to protect themselves.  

The decay is from a fungus and there is not anything that can be put on it to kill the fungus. But this is really not a overall health problem with the tree. If the foliage is green and full the tree is healthy. It sounds like the wood in the center of the tree is decaying and the tree may have some hollow places in the trunk. The living part of a tree is just under the bark and the bark protects the cells from decay fungi. When there is a wound to the bark decay fungi can get into the woody cells and start the eat away at the cells. carpenter ants some times make their nests in these decaying areas. The woody cells are dead cells and not associated with the healthy of the tree except for strength.
Trees can and do live many many years with their trunks completely hollow. Trees have the capability to seal off the decay fungi and slow the growth of the decay. IF the large limbs start to break off and the end near the trunk is decayed or hollow then the tree may have reached a point that it could be a hazard. And then it is only a hazard if it is locates near a structure that could be hit by a falling limb. Yours sounds a long way from that stage.

I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter and water it in  good, or wait just before a rain storm and fertilize and you will not have to water. This will increase the health of the tree and help slow the decay fungi. I would do this now and again after the leaves fall in the Fall.

Trees do not become hollow overnight - it can take decades - and while the center of the tree (the heartwood) may be decaying, the tree continues to lay down healthy wood (sapwood) around the outside of its trunk.  This results in the formation of a cylinder, the strength of which depends upon the percentage of healthy to unhealthy tissue.

The first sign of the tree being a danger is large limbs breaking off and these are hollow. This means the decay has reach the limbs and is fairly extensive.  

The living part of the tree is just under the bark not in the center of the trunk.

I would  treat for the ants and fertilize.