Question
Dear Jim,

I just finished reading an answer you gave to a person a couple of years ago regarding an oak tree he was fond of, and wanted to save, but had an infestation of carpenter ants.

I live in an area (Northern VA.) which is heavily forested.  This past summer and fall, we have had three strong windstorms, including the June Derechio, which took down several mature oak and yellow poplar trees, several of which fell on houses doing significant damage.  I have three neighbors who experienced this.  Because I have several very large, and very old oak and poplar trees adjacent to my house, I am very concerned about this.

The most recent tree which came down with Sandy , rootball and all, was a huge old oak.  The owner is having the tree cut up, and as I burn wood in my fireplace, I have offered to take some of the wood.  In splitting it this morning with a  wood splitter, I saw a major colony of carpenter ants in one of the brances. I could see where the ants got into the tree.  There was a small hole, where a small limb had broken of many years ago, and the trail of the ants was easy to see.  What I found interesting, was that the base of the tree, and most of the limbs, were solid through and through, and showed no damage from the ants.   From what I understand, and you can correct me if I'm wrong, but I have been told that carpenter ants do not consume the  wood, like termites, but make nests in the trees to winter over, where there's warmth and moisture.  However, they can and do hollow out significant sized areas.

What I'm wondering, is what role, if any, did these ants play in the falling of the tree.  And if little or none, I would like to know what I can do to help the health of some of the very old trees behind my house.  One which died a couple of years ago, and was cut down, had i40 rings near the base;  it was an old tree near the stream behind my house, with a diameter of about 5 or 6 feet, at least.   Can I, or should I fertilize the tree?  Old dead branches often fall from these trees, but as they are over 100 years old, that is to be expected.  They look healthy toward the top.

Please advise as to what I might do regarding carpenter ant colonies in these trees, and how I might help extend the lives of these beautiful old trees.  For example, does ground cover help keep the soil from drying out, or getting too damp?  Or mulch or wood chips?

I can tell from your previous advice that you are an extremely knowledgeable person, and very pleasant and courteous, as well.  I hope you can help provide the information that I need.  

Thanking you in advance.   Rob Ray

Answer
Carpenter ant nests are very common inside trees, especially older trees that are hollow or have a significant amount of dead limbs and branches. The nests are usually in rotted, decayed wood, although some nests may extend into sound heartwood in the center of the tree. The decay gets into the tree through a wound--in this case the branch was the entry port for the fungi. You are correct the ants do not eat the wood but take advantage of the decaying wood the fungi has infected and weakened.

I would fertilize the tree. Use 10-10-10 fertilizer at a rate of 1 lb. of fertilizer per inch of trunk diameter. Scatter the fertilizer under the tree from about 3 feet from the trunk outward to just beyond the spread of the branches. Water the fertilizer in good--apply the fertilizer just before a rains event and you will not need to water. Do this now and again in the spring. This will increase the overall health of the tree and help it fight the decay and the effects of any ants.  The ground cover for this large a tree is not necessary however I would try to keep the area natural so the soil will not dry pout during drought conditions.

Carpenter ants in trees are not directly harmful to the tree. Control is not essential for the tree's health, as the ants are only taking advantage of an existing situation of soft, weak wood in which to establish their colony. Stress, mechanical injury, environmental conditions, disease or other insects are responsible for killing limbs or sections of the trees in which the ants are able to nest. Once injury has occurred, wood decay can set in if moisture is present; it is the wood decay that gives the 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.  

I hope this answers your question. It is difficult without seeing the tree and the conditions it is growing in.