Expert: Jim Hyland - 10/19/2009

Question
We noticed 2 large black areas at the trunk of our old oak tree and wondered what it could be. the tree seems fine but this is an old tree and next to our house and we don't want to loose it.

Answer
If the dark areas are wet it sounds like a borer type insect. Spray the area with an insecticide called Onyx or Merit. Check with your local nursery for these insecticides. This does not mean the tree is doomed. Borers tend to attack trees that are under stress so 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 now and again in the Spring. It will take a lot of borers to kill and tree the fertilizer will increase the health of the tree and cause it to resist attack.