Question
QUESTION: I have an oak tree that died and was recently taken down.  The tree's inner wood appeared to be fine.  A layer just under the bark all around the tree about two inches thick was almost like sawdust.  This was also the case with a neighbors oak about 50 feet from this tree.  What my questions is how to prevent the spread to the other 5 large oaks in my yard.  I had the county agent come look and he said he thought it was a fungus on the tree closest to the downed tree.  I can not find anything on this or how to stop it on the one tree and prevent the others from becoming infected.

ANSWER: Sounds like a decay type fungi --these infect the woody cells and do not cause the death of the tree. They will not spread into other trees unless there is a wound. I would fertilize the trees 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 any the decay fungi that might infect the trees. . I would do this now and again after the leaves fall in the Fall. I see no problem that the disease will spread to the other tree.

There is a very small chance that this is oak wilt --do not know your location. IF so this can spread from tree to tree by root grafts. Here is a web link with pictures. I would call the local office of the State Forestry Agency and ask one of their Foresters to come take a look. I would guess it is not oak wilt but you need to make sure.  http://www.extension.umn.edu/distribution/naturalresources/DD3174.html

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QUESTION: The tree is located in TN just North of the GA and AL state lines.  Since the article referenced Northern states I think I will try the fertilizer and see what happens.  I think I will also contact a forester.  I have had the county agent and his suggestion was a spray with Durban.  I tried to obtain some from the Farmers Coop but, they required a "chemical" card.   

Do you think the chemical is worth the effort?  I have access to an exterminator who can supply an equal.

Answer
I really do not think it is oak wilt. So I would fertilize and this should do the trick. Durban is an insecticide and will do nothing for a disease so unless you are seeing some type of insect I would not spray the Durban. I really do not think you have a problem with this spreading to the other trees. Wait and get the County Forester to take a look.