Cut the tree down
Immediately apply a systemic herbicide to the fresh stump
Use a herbicide labeled for woody plants and follow the label exactly
Treat regrowth promptly with foliar herbicide when leaves are fully expanded
Recut and retreat any stump sprouts or suckers
Repeat treatments for multiple seasons until no regrowth appears
Remove root suckers as soon as they emerge
Dispose of cut material properly to prevent resprouting
Monitor the area regularly for new shoots and seedlings