This isn't that new, Yamaha has been selling a remotely controlled helicopter specifically made for applying insectcide on crops since 1991[0]. They were even used in aerial robotics research for a bit[1]. Helicopters are particularly nice for spraying crops because you have a nice turbulent downwash that pushes the pesticide onto the crops.

[0]https://www.yamahamotorsports.com/motorsports/pages/precisio... [1]https://en.wikipedia.org/wiki/Yamaha_R-MAX#Research