It used to be all the rage in the 1970's but not any more. I don't know if that is due to legislation or the practicalities of aerial spraying small fields. A lot of fields have trees and power lines in them and most will have a house right on the boundary, people that live next to farmland get vocal enough about spraying when we go past at 10kph with a tractor sprayer and I dread to think what they'd be like if a plane went over at 90mph spraying, they'd have heart failure!