T28D:
If you have a look at a modern aerial applicator, like a turbine Airtractor, Thrush etc, you will note that not only do they have txp and radio, but a very sophisticated GPS system that allows them to do away with markers and the like. They apply the chemical with little or no overspray because of the possibility of legal action from neighbours who possibly don't want that chemical drift onto their land. Depending on the system it is quiet feasable, according to some, to run a wire to some box that gives ADSB qualities.
Some are getting up in the weight catagory, so I don't know if they would qualify for the "subsidy" even if they did want it.