Driver less cars currently motoring all over LA, Chicago, and NY.  If they can maneuver past those obstacles in that environment, they will figure out how to spray my crops I'm quite certain.  5-10 years and the insurance space will be preferring a pilot less machine.  In some places, the work comp will alone offset the robot costs if you can find the labor in the first place.  My 2 cents.  The stuff they are doing in the DARPA challenge right now will blow your mind.