Drilling is a method regularly used by Bush regenerators to kill weed trees. It takes less time and is less labour intensive compared to chain sawing and is very effective. Leaving the tree standing keeps the roots in the ground and so holds soil in place. For species like Umbrella tress that re root when placed on the ground, this method saves a lot of time removing or rafting the branches as they die in situ.
Drilling trees and leaving them to die is not suitable for gardens or situations where falling branches or trunks could land on people or property. It can take many years for the trees to rot and come down and this needs to be considered before using this method.
To drill a tree, use a 10m auger drill bit. Drill around the bottom of the tree at close intervals, about every 10 cm. Go in 2cm, remove the drill and fill with a 50/50 Glyphosate mix of 360g/L concentrate. Going deeper or using a stronger mix wont get a better result.
This method works well on Camphor laurels, African tulip trees, Broad leaf pepper trees and Umbrellas. It also works on Palms but the drill needs to go into the middle of the trunk.