More farmers are failing to comply with the rules for planting genetically modified (GM) corn than the biotechnology industry claims, according to a new study of government data. Almost 20 percent of U.S. farms growing BT corn, the main type of GM corn, violate the rules for doing so, according to the Center for Science in the Public Interest. Those rules require farmers to plant at least 20 percent of their acreage with non-GM corn; 19 percent of surveyed farms that were not meeting that requirement, and 13 percent were planting no other corn varieties at all. The industry reports a noncompliance rate of 14 percent. The authors of the report said it showed that the government should stop counting on biotech companies to enforce the rules; currently, the companies monitor compliance through telephone surveys.