last time i check farmers grew crops and raise animals that we eat. that has nothing to do with immigrants. one thing i can tell you is we would have way less shoddy made houses.
Farmers are able to sustain a more yield with a larger group of cheap labor. I was on vacation in Machias, Maine a couple of weeks ago right during blueberry harvesting season. Passed a few groups of workers, mostly Somalian, doing the picking with a local leader. The USA is really big