I own a farm also. The land is usually sprayed before the corn is planted also. Usually 2-4-D and Cimmaron. Cimmaron will kill any broadleaf vegatation, including MJ. I would never grow on another man's land. It's just wrong. I've seen responses in this thread from a broad spectrum of people, from straight up guys to boneheads that would most likely rat thier best friend out.
If you're going to do this, at least wait until the corn is too tall to be cultivated. Look around the farmers barn to make sure he doesnt have a highboy. A highboy is a sprayer/cultivating plow tractor thats jacked up really high to drive between the rows without knocking the corn down. If he does'nt have one, wait until it's over 1ft tall so there's no chance it'll be ran over.
Farmers do check thier crops. They also build fences, bushhog around thier fields, and may even grow thier own weed
. We notice things like paths, bent over and cut fences, etc. Make sure your stealthy.
Farmers don't pic field corn until up in November sometimes. Always October or later. But they will chop field corn for insilage starting in September sometimes. Usually around end of September. You'll be able to see a corn picker around his barn somewhere if he picks or a chopper if he chops. If you've lived there awhile, you've probably seen them harvesting and you should know which methods they use. If you see them start harvesting before you have harvested, you better hope for rain bud
Good luck, but remember, do what you feel is the right thing. You have your own land and you say there's no threat of helis. You have to make a rather large circle in corn to get the right sun for patches of the size your spoke of. Corn can get 10-15ft tall or taller. You'd prolly need a 20ft circle. If a heli does fly over, you're screwed. They'll find the weed, find your paths, set you up, and you know the rest. Good luck!