The American Seed Trade Association (ASTA) has asked USDA to set a standard for what is allowed to be tagged as non-GMO seed. Currently, no standard exists.

ASTA suggests a standard of 1%, which works out to 800 GMO seeds in a typical bag of seed corn and 1,500 seeds in a typical bag of soybeans, says Bill Wiebold, University of Missouri agronomist.

“The request for allowable limits of genetically engineered contamination illustrates how difficult it will be for farmers to guarantee GMO-free grain,” the agronomist points out.

Corn is cross-pollinated and therefore more susceptible to GMO contamination than soybeans, which are self-pollinated. Because of the complexity of assuring non-GMO grain, Wiebold encourages producers to test spring seed as well as fall grain.

“Farmers should be extremely careful as to what they say about their grain,” he says. “Don't ever swear in writing that your grain is free of GMO contamination.”