Question
Hi Jim,I live in western Pennsylvania(Pgh.)and recently noticed a spot on one of my oaks. It is on the trunk about 3 feet from the ground and about 3inches in circumfrence. The bark is dark brown and when I probed it with my fingerI discovered the wood in this area is dark and rotted. The tree is quite large and is blooming well and otherwise appears healthy. If you can,please advise me on what you think this is and what if anything I can do or watch for. Thanks!

Answer
This sounds like a oak borer--an insect that bores into the trunk and the tree exudes sap making the spot on the bark. I would spray the trunk where the wound is with an insecticide called Merit. Check with your local nursery for this product. If it is not too large a tree you can use a product called Bayer Advanced tree and shrub insect control. This is applied to the soil around tree and the root transports the insecticide to the trunk and branches and when the borer feeds on the wood it is killed. It is more expensive than the Merit spray but easier to use and will last for the growing season.  Here is a web link to more information on the Bayer product.

http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html