Hello,

It is important that you know what you are dealing with before you attempt to control the insect. If you have an ash tree, ash borers have been a significant pest for the last few years because the drought conditions have weakened many of the ash trees.  However, it seems a little late in the summer for the ash borers to be active. Are you seeing any insects now or are you talking about evidence of insect activity such as holes in the trunk?

If it is possible for you to take several close-up photos of the insect in question and attach it to a reply email, I would try to identify it. That would make it possible for a recommendation for the correct treatment to target the particular insect. Also, if you could take pictures of your tree and the evidence of the insect, that would be helpful too. If you have holes in your trunk, you should know that repeated infestation by borers can kill your tree. Treating your tree at the appropriate time with the appropriate insecticide would help fight against further infestation.

In the meantime, following are links to some information about ash trees and the ash tree borer.

http://www.ext.colostate.edu/ptlk/1735.html

http://www.ext.colostate.edu/ptlk/1425.html

http://www.ext.colostate.edu/pubs/insect/05530.html