“The corn is as high as an elephant’s eye”
Elephants not being overly common in Oklahoma, I wonder how they knew when to harvest it.
Corn that grows "as high as an elephant's eye" is putting a lot of its energy into the stalk. Most corn around here (central PA) is bred to grow shorter, and have more energy for its kernels.
Different breeds of corn have different growing seasons and resistance to drought. So farmers chose the corn they hope will do best for their own particular environments.
When field corn is "finished" the whole stalk turns brown. But farmers are paid for corn by weight, less the moisture content. That's why some let their corn stand long after it's ready for harvest, so that it will somewhat "field dry" and save them the cost of having it mechanically dried.
It doesn't hurt field corn just to stand there weeks or months after it's ready for harvest.
In some years a corn crop fails, due to drought or cold weather, etc., and farmers will give up on producing sale-able corn. At that point they harvest whatever they have while it's still green, chop it up into silage and feed the whole thing to their livestock.
That's the only time I know of when they harvest green field corn. But maybe out west they do things differently?