It appears that the anti-immigrant moves within the U.S. are working, but alas, creating some unintended consequences. According to today's Washington Post, farmers in California cannot find enough laborers to pick their fall harvests. Why is it that able-bodied Americans have not rushed in to take advantage of these opportunities? Probably the same reason why citizens left farm labor years ago: it's back breaking work and pays poorly (and it always has).
Farmers quoted in the article explained the situation like this: as the border tightens and crossing becomes more dangerous, expensive and difficult, Mexican workers who once spent part of each year in American fields without a work permit are reluctant to back to Mexico, fearing that will not be able to return when they want to do seasonal work. As an alternative, they settle in the U.S., take year-round jobs that pay more and are less laborious than farm work. These jobs include construction, landscaping, and hotel service jobs.
There are other industries that offer low barrier to entry work which pays well. These industries also depend on immigrant labor and, "are also concerned about the overall availability of labor given demographic trends…" and added, “But agriculture is the warning sign, if you will, of structural changes in the economy."