Deputy Agriculture Secretary Kathleen Merrigan sees an epidemic (流行病) sweeping across America’s farmland. It has little to do with the usual challenges, such as flood, rising fuel prices and crop-eating insects. The country’s farmers are getting older, and there are fewer people standing in line to take their place. National agricultural census (普查) figures show that the fastest-growing group of farmers is the part over 65. Merrigan is afraid the average age will be even higher when the 2012 statistics are completed.