Okay Grant on the first part about the "free trade ".
On your second point , like I said the INS imposed new guidelines on the whole seasonal Mexicans helping out the Califirnian farmers .New tarifs also , check out the USIC website , btw the price for getting a green card for example has jumped from 275$ 2 yrs ago to a cool 1000$ . Anyway so the farmers tired of all the administrative paperwork , placed ads in their local communities some in papers out of Sacaramento and San Francisco , pledging higher wages .
Number of people who showed up for work--> ridiculously low
Number of people that stayed throughout the season --> 0
It was on PBS and CNN, I ain't making it up.
Check PBS website you may find something on it , not sure .