We need to kill a healthy willow tree that's approx 30ft high. We can't cut it down so need to be able to destroy it were it stands.
Killing a Healthy Willow Tree
Certified GKH Gardening Expert
Since the tree is so large, you may want to consult with an arborist to prevent the possibility of having the tree fall once it's dead, or even have a professional come in a take the tree out. That being said, other than cutting the tree down, the suggestions in this article may help: https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-kill-a-tree-killing-trees-in-your-garden.htm