I made a DIY 'injection' system for one of my trees.

I drilled 10mm holes at an angle (they recommend 3) to the centre of the trunk then inserted a thin plastic tube, sealed the space between the tube and trunk with silicon then filled an old fairy liquid bottle with chemicals, made a small hole in the bottom of the bottle, connected the tube to the top of the bottle spout and hung it upside down above the hole.

Job done!