Pesticide residues were found on conventional crops four times more often than on organic food.
"I'll still rely on conventional crops on the rest of the farm.
Sanders added the research showed organic cereals have less protein than conventional crops.
The researchers found much higher levels of cadmium, a toxic metal, in conventional crops.
Two years ago, he gave up and started growing conventional crops again.
Even companies that use conventional crops in production have to work hard to get certified.
The problem has also arisen this year in Europe, where genetically modified material was discovered in supposedly conventional crops.
When farms switched from conventional crops to the engineered varieties, there was no substantial change in yields.
But pollen from those crops can spread in the air from field to field, intermixing with pollen from conventional crops.
Without any action, Mr Vilsack argues, courts will dictate the future of GM, organic and conventional crops.
"They are recognizing that there is a likely or future problem with contamination of conventional crops with genetically engineered varieties creating potential health risks," he said.
