Farmers are timorous. If they would try to hire Americans at what the market would require, they would only have to raise the price of a head of lettuce or bag of apples by a nickel or dime a piece. And the good PR would make everyone feel good about the extra spare change. But like I say, they are afraid.
Wait a minute...I grew up in Illinois...and how much lettuce, or vegetables or berries are picked in Ohio....I expect not much....where did you come up with that nonsense about migrant workers....now the picking of sweet corn is something that we in Illinois when I was a kid 50 years ago...was done by mexicans...in small numbers, but nevertheless they were there...and I expect most were legal!