Margaret Hamburg, a FDA commissioner, said "About 15 percent of our food is imported, and in some categories that percentage is much higher. For example, half of our fruits and a fifth of our vegetables come from abroad."

Source: Margaret Hamburg, M.D.  “Basing Food Safety Standards on Science and Prevention Posted on January 8, 2013 by FDA Voice.  http://blogs.fda.gov/fdavoice/index.php/2013/01/basing-food-safety-standards-on-science-and-prevention/