The U.S Department of Agriculture has estimated that half of the immigrants tending to the crops of Californian farmers are unauthorized.

Now there is less migration from Mexico and an ageing farm worker population, this causes a problem as domestic-born workers are unwilling to take their place in the agricultural sector.

This has resulted in farmers taking certain measures. Some farmers have begun planting fewer acres or have switched to less labour-intensive or machine-operated crops, whilst others have moved their operations to Mexico where they can hire larger crews.

Guadalupe Sandoval, executivedirector of the California Farm Labour Contractor Association has said "It's made for a lot of competition out there in trying to secure adequate crews. We're seeing vineyards ripped up and replaced with almonds, certain raisins replaced with new varieties that will be machine-harvested instead of hand-harvested."

The number of full-time field and crop workers in the U.S dropped by about 146,000 people between 2002-2014. The decline has been more pronounced in California, which produces half of the country's fruits, nuts and vegetables. The state's number of full-time workers declined by 85,000 between 2002-2014.Compared to 15% in 1989 and 1991, half of crop workers between 2007 and 2009 were not authorized to work in the U.S.