I have a Commercial made Root Injector that hooks to a Skid Sprayer Hose. It was mostly used for termite work. But that might be more equipment than you need.
A quick trip to the Hardware store for a small ID galvanized Pipe and some fitting and you can make your own. Our Florida Sandy Soil is not that hard to push a pipe into. Grind a sharp point on the pipe or even heat it up and hammer it flat before grinding will make the Job easier.
Rittenhouse sell this model for big money and I could make several for the price of one they sell.