Question
Hi Jim
I had 3 Oaks growing in a cluster for the past 7 years...they are probably 30 years old and we lost one last year and just had it cut down.  The wood had what appear to be worm holes in them.  The two remaining one in great condition and the other is covered with moss and looks ill...not many leaves and a lot of small branches are falling off the center of the canopy.  Literally the healthy Oak is just about 20 feet from the sickly one.  Their canopies actually are grown together.  I have so far treated the sickly Oak with 'Bayer systemic insect killer' Only once and then put tree fertilizer spikes out at the canopies edge.  I also pulled the dead weeds from the base of the tree where there were a lot of beetles and bugs in the soil.  I have heard that you are not supposed to mess with an oak, but this one was doing so bad that I thought I should do something before we loose it too. What are your suggestions?

Answer
Just not enough information to answer this question correctly without looking at the situation. It is not the larvae (probably Betsy beetles) that you found in the wood when you cut the dead trees--these insects are taking advantage of the dead and just helping decay the wood. I would guess a disease--hypoxolon canker or maybe oak wilt--depending on where you live. I would contact the local office of the State Forestry agency and ask one of their Foresters to cone out and look at the trees. After examining them they should be able to ID the problem.

Fertilizer will help both of these diseases but not the spikes--10-10-10 fertilizer is better and cheaper--scatter it around the tree at the rate of 1 lb of fertilizer per inch of trunk and water it in good --apply just before a rain storm and you will not have to water.