Abstract: A tree treatment capsule is disclosed as including a head element having a shank portion with an internal cavity containing a chemical agent. The internal cavity is sealed by a plug in an end of the shank portion remote from the head element. The head element, shank portion, chemical agent and plug form a self-contained unit which is inserted into a pre-drilled hole in a tree. The shank portion is made of a frangible material so that upon breaking as a result of an impact force applied to the head element, the chemical agent is free to mix with the sap of the tree.