Seriously? That is a completely different animal from the drone portrayed in the article. Anything in that league wouldn't be anywhere near cost effective vs. something like a conventional crop sprayer plane.
I am serious that I can envision a drone that could be used for crop dusting. I personally wouldn't use a quad copter, but probably something more like a 20-30 foot flying wing powered by a small gas engine. My example of a predator drone was to illustrate that it is entirely possible to design a UAV that greatly exceeds the specs needed for crop dusting. I also think most people here are vastly underestimating what a Agricultural UAV is capable of. Take a look at this page https://store.tmotor.com/product/P80-v3-pin-kv100-p-type.htm... and some of their possible configurations.
I think just adding a gas engine to a quadcopter would give it enough endurance to make it useful. Obviously a crop duster is going to be fairly large to start with - it needs some space just to store the things it will spray.