I also find it strange that the scythe is an exotic weapon which requires a special feat to even dare to pick up and use, whereas farmers who use them in droves are seldom known for their weapon training. Of course, according to PnP rules, one may pick up and use an exotic weapon, they just recieve a -4 to swinging it in battle since it's so strange and unweildly in such a situation. A large field of grain is not likely to have an AC above 4, considering it's size gargantuan and effectively immobile, and is incapable of battle.