About the study:
The above article is about this Bloomberg (i.e. pro-illegal immigration) report, which is not what I’d read, but is similar:
http://www.renewoureconomy.org/sites/all/themes/pnae/nc-agr-report-05-2013.pdf
Similar stories from 2011:
2011 NYT article: http://mobile.nytimes.com/2011/10/05/us/farmers-strain-to-hire-american-workers-in-place-of-migrant-labor.html
// It didn’t take me six hours to realize I’d made a heck of a mistake,” Mr. Harold said, standing in his onion field on a recent afternoon as a crew of workers from Mexico cut the tops off yellow onions and bagged them.
Six hours was enough, between the 6 a.m. start time and noon lunch break, for the first wave of local workers to quit. Some simply never came back and gave no reason. Twenty-five of them said specifically, according to farm records, that the work was too hard. //