Who planted the corn and with what?

Rating: 6/10 (25 September 2019)

As a farm kid, I found one glaring problem with the movie: the existence of huge fields of corn, which were the setting for much of the action. As the aliens have already been on earth for something like 472 days (as mentioned in the movie), how did the corn get there? The corn would look much dryer and deader if it had been planted before those 472 days. If it was planted after the aliens arrived, how did they manage to use a tractor and farm equipment without the aliens hearing them? No way all those perfectly manicured fields were done by hand!
Otherwise, I enjoyed the storytelling and the actors. It wasn't completely scary but that's fine because I don't really like super scary movies.