"(Border crossing) is more dangerous because of the drug cartels, our government is doing a better job of enforcing the borders and the Mexican economy is doing better," said Jim Lincoln, a vintner and former president of the Napa County Farm Bureau.

Phil Martin, professor in the Department of Agricultural and Resource Economics at UC Davis, paints a different picture. He estimates the yearly number of farm laborers has remained steady in the last decade at around 800,000 people after it had expanded in the 1990s.

Martin is skeptical of perennial farmworker shortage warnings, finding no signs of diminished crops or fewer workers in a 2007 report, but five years later he says the farming community has hit "a period of uncertainty."