Okay, next idea... Inject full strength Brush Killer under the bark. You can do this by peeling a little bark back and dumping it in or drilling small holes and pouring it in. This is a good time of year to start this project as the nutrients are heading down to the roots for the winter.
You only need to get under the bark as the cambium layer of the tree is the only one that needs to be poisoned. Depending upon the tree and age, sometimes you can loosen a pocket under the bark and pour the Brush Killer in.
Disclaimer: Who me?
