At 54 yrs I am sure like several others have said, that I could hold a days work in the field. I still clear land, plow, plant and harvest today. Nothing like sweating in the Florida sun to clear out your system. That being said the OP wonders where the help will come from to harvest large quantities of crops. Under our current system there are millions of people who are receiving more from the Gubment Teat for not working than what legal migrant workers are making for honest work. Until this glaring fact is changed there will be a multitude of people who WILL NOT work. hence the need for migrant workers.
I agree with Saddlebum that we need an effective LEGAL Guest Worker program , without achor babies and handouts.
I started working on a tobacco farm in North Carolina at age 12 for three summers, pushed a broom and mop, and unloaded trucks throughout high school, cleaned horse stalls, shoveled out pig, sheep, and goat dung as well as hauling wheelbarrows of cement during college. I never went hungry because I could and WOULD find some sort of work to cover my minimal costs of living.
2nd Thessalonians 3:10 "For even T)'>when we were with you, we used to give you this order: U)'>if anyone is not willing to work, then he is not to eat, either."