Weeping willows have a strong root system that chases water throughout the soil. Willow roots will attack other plants' resources and grow into sewer or septic lines if planted too close to the home. When removing an established willow tree, it is important to kill the roots. Even cutting down the tree will not completely kill it if the roots are alive. It is not unusual to see a willow tree grow back. Using chemical herbicides will usually destroy the root system.
Cut the willow trunk as close to the soil grade as possible.
Drill holes into the tree trunk spaced every 5 to 7.5 cm (2 to 3 inches) around the circumference. Make the holes at least 2.5 cm (1 inch) deep.
Inject the holes with an herbicide approved for the willow variety you are trying to kill. Mix the herbicide according to the packaging instructions. This is a legal requirement in most areas. Let the trunk rest for 12 months undisturbed to let the willow roots absorb the poison.
Remove the tree trunk with a back hoe. Pull out any remaining roots by hand.