Question

Red Oak Tree Bark   Have a Red Oak tree in my back yard and noticed that its bark has become brittle and many boring holes exist/cracking? When I tap on trunk, ants/insects come out and appear to be the culprit. Wonder if you can tell by picture what may be causing the issue and how should it be treated? Tree is healthy otherwise, green and growing.

Answer
looks like a couple of things going on with this tree. The trunk has a wound that has allowed a decay fungi to enter the wood. And borers have also entered the trunk. You can spray an insecticide on the bark of the oak where the borers have entered and this will kill the insects under the bark and in the wood. Use an insecticide called Onyx or Merit. Check with your local garden type store for these.

There is not much that can be done about the decay fungi.A decay fungi enters the woody part of a tree through breaks in the bark. Over time the fungi eats away at the woody in side the tree trunk and in many years will cause the trunk to become hollow. A hollow tree is not really that bad. the tree can lose some strength but the health of the tree is not effected.  There is not a fungicide that will control the decay fungi. Wound treatment paints do not prevent invasion of the wound by wood decay fungi and therefore are of little benefit. Maintaining tree vigor through proper pruning, irrigation and fertilizing practices will help to reduce potential decay problems by promoting the trees natural wound response processes. decay fungi infect dad wood cells and do not infect the living cells so by itself the decay fungi will not kill the tree.  
I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. Do this in the spring. If you put the fertilizer out just before a rain storm you will not have to water it in.
Signs that the tree is getting into trouble with strength is large limbs breaking and the end of the limb near the trunk is hollow. This would mean the decay has grown into the upper parts of the tree and the falling limbs could be a hazard if buildings or structures were near the tree.
In your case this should be many year down the road and maybe not at all.

If the bark where the fungi conks are growing gets loose you can cut it off back to solid bark and this will help the wound heal faster but an area this large will take many years to heal over.