That's problematic if the US government cannot ensure that Mexican fields of lettuce, carrots, strawberries, and onions are free of dangerous bacteria or pesticides. Neither the FDA nor its Mexican counterpart requires fresh produce growers to be certified before they send food into the US.
The FDA does screen products at the border, targeting those products and producers that have posed problems in the past. But a 2008 Government Accountability Office report showed that the FDA examined less than 1 percent of the fresh produce coming through its borders between 2000 and 2007. So almost all the food that reaches the US passes through without being physically examined at all.
Earlier in the decade, outbreaks of food-borne illness in the US were traced back to Mexico – including a 2003 incident that linked hepatitis A with Mexican green onions and salmonella as well as outbreaks of illness blamed on Mexican cantaloupes in 2000, 2001, and 2002. These incidents spurred the Mexican industry to clean up its image by developing various voluntary standards. For example, México Calidad Suprema is a generic brand that growers and packers commit to operate by high food-safety standards.