The increasing demand for non-GMO grain in Europe and Asia makes it important for producers to be familiar with testing requirements, says Bill Wiebold, a University of Missouri agronomist.

Contracts should specify purity requirements as well as which party is responsible for testing and any consequences for excess contamination, says Wiebold.

He lists three main methods of testing for biotech traits:

- Bioassays are useful for herbicide tolerance traits but less so for Bt corn and cotton, Wiebold says. A bioassay involves germinating seeds in the presence of herbicide or spraying recently emerged seedlings. Detection levels may be as low as 0.5%.

- ELISA, or Enzyme Linked Immunosorbant Assays, use antibodies to detect proteins produced by genes inserted during the biotech transformation process. ELISA cannot quantify the amount of GMO contamination, but is sensitive to amounts as low as 0.5%.

ELISA is inexpensive but unacceptable for specialty markets.

- PCR, or Polymerase Chain Reaction, tests for the actual inserted gene. At around $100 per sample, PCR can be quantitative and can measure GMO content as low as one-tenth of 1%.

Avoid any contracts with impossible tolerance demands: "Less than 1% for soybeans, less than 2% for corn," Wiebold advises.