China has rejected nearly 1.45 million tons of U.S. corn shipments since late last year, according to a U.S. grain industry association, the Wall Street Journal reported on Friday.
The National Grain and Feed Association (NGFA) estimates that China's rejection of genetically modified corn has cost grains companies $427 million in lost sales and re-routed shipments.
China began rejecting cargoes in November last year after detecting Syngenta's unapproved MIR162 strain in incoming shipments.
The industry group, which bases its number on data from exporting companies, says exports of corn and related products from the United States to China since January are down 85 percent from the same period last year.
China is the third-largest buyer of U.S. corn and has approved 15 genetically modified corn varieties for import.
Syngenta's MIR162 has been awaiting approval since an application was submitted in March 2010, although it has been mixed in with other varieties since China started to import U.S. corn in 2011.
Rejections of the Syngenta strand have affected the price of corn and soybeans on the global market, resulting in hundreds of millions of dollars in losses for farmers, the report says.
Grains companies have been frustrated by what they say is an opaque process of approving and rejecting genetically modified crop strains in the world's fastest growing corn market.
Soybean prices have been under pressure after news on April 10 that Chinese importers have defaulted on at least 500,000 tonnes of U.S. and Brazilian soybean cargoes worth around $300 million, the biggest in a decade, as buyers struggle to get credit amid losses in processing beans.