The best way to destroy it is to purchase Roundup concentrate, cut the tree about six inches from the soil line, paint the cut stub with rounduup concentrate using a paint brush, and covering the stump with plastic wrap and tape. (This prevents it from running down and killing nearby plants. The best time to do it is summer and fall when the roots are more likely to suck in the poison. You may need to repeat this in the spring if any suckering occurs from plants not totally killed by one fall application.

Thank you for the speedy reply.  Does it help to drill holes in the tree stalk to get the Roundup in?  I saw that as one suggestion when I googled my dilemma. 

The best way to destroy it is to purchase Roundup concentrate, cut the tree about six inches from the soil line, paint the cut stub with rounduup concentrate using a paint brush, and covering the stump with plastic wrap and tape. (This prevents it from running down and killing nearby plants. The best time to do it is summer and fall when the roots are more likely to suck in the poison. You may need to repeat this in the spring if any suckering occurs from plants not totally killed by one fall application.

Sorry, I meant to respond to your question. What you want is for the tree to absorb as much Roundup as possible. By putting holes in the tree transport system I think you might slow absorption down by blocking the path to the roots.. Roundup takes about 3-5 days to get absorbed into the roots and kill the plant tissue. In a week you could cut the tree trunk down another inch or two and repeat the treatment. I think that would serve better thanRoundup in holes in the tree.

Thank you.  Your response makes it very clear.

You are welcome.