The National Grain and Feed Association (NGFA) says China has rejected nearly 1.45 million tons of U.S. corn shipments since 2013,costing grains companies $427 million in lost sales and rerouted shipments.

China began rejecting genetically modified corn in November 2013 after detecting Syngenta's unapproved MIR162 strain in incoming shipments.

The NGFA says exports of corn and related products from the U.S. to China since January are down 85 percent from the same period one year ago. China is the third largest buyer of U.S. corn.

Fifteen genetically modified corn varieties are approved for import to China. Syngenta’s MIR162 has been awaiting approval since March 2010, but has been mixed in with other varieties since China started importing U.S. corn in 2011. Rejections of the strand have affected corn and soybean prices on the global market, and resulted in losses of hundreds of millions of dollars for farmers.