I’ve read you can do either but chemicals are not required.
If I understand it correctly, the nutrients from the ground travel on the inside of the tree and the respiration exchange happens in the crown and then is transferred down the outside layer just under the bark. Girdling that outside layer disrupts the cycle and the tree dies without sending up shoots all over the place as distress response.
It’s like a buck killing a tree by rubbing off the bark ...except I used a chain saw.
It’s working on two for sure and not so much on two (those two on the right in post #1).
Sent from my iPad using Tapatalk