Question
I bought a home with an outdoor deck built around a lovely mature shade tree. I am not sure of the variety, I have mostly red oaks but this tree puts out 1" long x 1/4" wide flat seed pod in the fall. The problem is a large cavity in the side of the tree's trunk about 5 ft from the ground. This cavity is about 12" tall by 4" wide and deep enough to appear to be more than half way into the center of the trunk. I am so afraid of losing the tree, but don't know how to save it? Any suggestions would be helpful! Thank you!!   Carol in Bartlesville, Oklahoma

Answer
If a trees bark is wounded fungi can enter and start to 'eat away" the woody part of the tree. These are decay fungi and do not damage the living cells but only decay the dead woody cells on the inside of the trunk. What the decay fungi can do over a long time cause the trunk to become hollow and could weaken the trunk causing it to break in high winds. There is not really anything that can be applied to the decay to treat it. It is like the decay in a tooth but the location is such that the old wood can not be cleaned out as a dentist would do to a tooth. There are products that can be applied into the cavity filling the gap. These do not stop the decay but can strengthen the trunk. A more recent cavity treatment involved filling the cavity with a urethane or polyurethane foam to fill the hole. It was believed that when the foam expanded it would eliminate all the air in the cavity and prevent the accumulation of water. Besides, the foam was supposed to be flexible and move with the natural movement of the tree. This is more aesthetic than anything.

The best thing would be to keep the tree growing healthy by making sure it has enough water and fertilizing it once a year. Fertilize with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. Water once a week with 1 inch of water --place a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop. Do this if it does not rain.