A method of making a tree injection device includes identifying a species specific depth at which phloem is located beneath a tree's bark and preparing a tree injection device. The tree injection device has a head defining an input opening for receiving the solution and a shank. A shank of the device has a radially constricted section positioned between a first radially enlarged section and a second radially enlarged section. An output opening for delivering the solution is defined by the radially constricted section and is formed at a distance from a collar substantially equal to the depth.