Question
I have a beautiful cherry blossom tree that I am concerned about. My husband discovered that a few of the trunks are hollow and he thinks ants are living in there. The tree looks healthy - it just finished blossoming. How do we get rid of the ants and fill the hollow trunks so we don't lose the tree. Someone told us to fill the trunk with cement but that didn't sound right.

Answer
When the bark of a tree is damaged decay fungi can enter and over time cause the tree to become hollow. The living part of a tree is just under the bark and the decaying woody cells are not alive and will not cause health problems to the tree beyond possible loss of the trunk strength during wind storms. But even this is not a concern if the tree is kept healthy. Filling with cement will cause damage from the cement being nit flexible and the tree moving during wind storms will rub the wood and cause problem. There is very little that can be done for decaying trunks. Like a tooth you would heave to remove all the decay before treating the sound surface--for trees this is not possible. You can use any type of insecticide that will control ants and spray it into the hollow and use an ant bait around the tree. You can use spray foam for installation to fill the hole in the trunk. This is just for cosmetic purposes and will do little for the treatment of the decay.

I would fertilize the tree with 10-10-10 rate the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. This will increase the health of the tree.