An excellent article by the "Agricultural and Resource Economics Update" from the Giannini Foundation of Agricultural Economics of the University of California regarding the future of farm labor for California growers and beyond:
http://giannini.ucop.edu/media/are-update/files/articles/V16N4_1.pdf
Following the statement summarizing the author's research showing that the era of farm labor abundance is coming to an end, arrives the money line:
"This means that immigration policy will cease to be a solution to the U.S. farm labor problem in the long run and probably sooner. In fact, we already may be witnessing the start of a new era in which farmers will have to adapt to labor scarcity by switching to less labor intensive crops, technologies, and labor management practices."
Seriously recommended reading for those in the berry business.