Question
Jim,

I have three weeping willows in my backyard (Cincinnati, Ohio).  One of the trees has some sort of insect that has bored into the bark and left dark spots of approximately 1 - 1 1/2 inches in diameter.  The tree is approximately 8 years old, has been very healthy, gets regular watering in the summer heat.  I can take a picture and email it to you if that would help.  Any ideas on what this is, and do you have an idea as to how to treat?  I am looking forward to hearing from you.

Answer
There are several borer insects that will attack willow. I would suggest that you spray the area of the trunk with an insecticide for borers. Check with your local nursery/garden type store for an insecticide for borers. These insects are deep in the wood and are hard to get to so repeat ed applications of a week apart may be needed. You can also take a knife and dig into the bark and wood where the attack is located and may kill the larvae of the borer that way--if you do this I would also spray the wound area.
Here is a web link to one of the willow borers that will give more information on the insects
http://oregonstate.edu/Dept/nurspest/poplar_and_willow_borer.htm