Many Helicopters for agricultural use are commercially available, but it is interesting that an Rcer developped helis with RC technologies.
Currently amazing technologies on RC heli and plane are introduced every day. With these known technologies, you can build your own heli for your special use. Here is an example; Korean RCer developped Heli for spraying agricultural chemicals. In the mountain area, planes are not proper to use this purpose, but small helis are more efficient to spray agricultural chemicals.
Using auto giro and GPS, this heli is self-positioned. Here is a video: http://youtu.be/dpbdBo-Dq2M
Please, notice the differnce between two helis; one has tail rotor attached on the heli fuselage and another has tail rotor positioned with the rotating plane of the main rotor.

Regards to all RCers