I do not know of a drone that will do what you want.  The larger spray drones don't have long enough battery life to suit scouting and they aren't nearly as swift or agile in the air.  From the description of your situation, I would keep the self propelled sprayer, add a scout drone, and hire a good custom applicator to spray fungicide on corn.  If there were an all-in-one drone, it might cost more than having two separate drones for scouting and spraying anyway.  Lol.

BTW, I run a T40 to spray and a Mavic 3 Multispectral for scouting and mapping.