Published in the Chat 'n Chew Cafe, March 2000

Minimizing Pollen Drift & Commingling of GMO and non-GMO Corn Grain

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-1150

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GMO: Genetically Modified Organisms

The great debate over GMO crops, also known as transgenic crops, continues in many circles of both the consumer and scientific worlds. Regardless of where you stand on this issue, farmers will be directly affected this fall if some grain buyers establish a strict threshold for minimum GMO content in the grain they purchase.

GMO "contamination" of non-GMO grain can occur in corn by virtue of either cross-pollination between adjacent fields of GMO and non-GMO hybrids or by commingling (a fancy term for "mixing") of seed. The latter can occur at planting time as farmers switch from planting one hybrid to another via seed carryover in the planter. Commingling can also occur during or after harvest time via grain mixing in the combine, trucks and wagons, drying facility or the storage facility. (Author's note: Fortunately, cross-pollination is a negligible issue for self-pollinated crops like soybean.)

Because the potential exists, albeit uncertain, for some grain buyers to limit their purchases of GMO corn grain this fall, Indiana corn farmers should make plans now for minimizing the potential for GMO "contamination" of any non-GMO corn grain that they intend on producing.

Seed purity

Obviously, production of "pure" non-GMO grain begins with the seed. Seed of non-GMO hybrids may not be completely GMO-free because of less than perfect quality control during the seed production and processing operations. For your subsequent protection, ask for assurances of purity of the non-GMO seed you purchase and plant. If your seed company will not share the exact purity levels, ask them to at least tell you what their own seed purity standards are.

Volunteer corn

Avoid the possibility of volunteer GMO corn plants in your non-GMO corn fields this year by avoiding planting into last year's GMO corn field. Pollen drift from such volunteer plants will result in some level of contamination in this year's grain production.

Planting operations

To avoid the risk of GMO seed carryover in the planter when switching hybrids, organize your planting schedule to plant your non-GMO hybrids first and GMO hybrids last. This advice also applies to your planting of GMO and non-GMO soybean varieties.

Planting date & hybrid maturity

To a limited degree, it is possible to manipulate planting date and relative hybrid maturity to minimize the potential for pollen drift or cross-pollination between adjacent fields of GMO and non-GMO corn hybrids. Planting early maturity non-GMO hybrids first, followed with later maturity GMO hybrids last will reduce the chance for pollen from a GMO field to "contaminate" the silks of an adjacent non-GMO field.

Bear in mind that this strategy is not perfect because of interactions of corn development with weather patterns and because the range of hybrid maturities you have purchased may not be that great. Obviously, this strategy is difficult to implement if you do not have control of the adjacent corn fields.

Consequence of insect refuge areas

Remember that the EPA recently mandated that farmers who plant Bt corn hybrids in 2000 must also agree to plant at least twenty percent of the land area to a non-Bt corn hybrid to minimize the genetic selection pressure for Bt resistance in the European corn borer population. The non-Bt refuge areas will, by default, cross-pollinate with the Bt hybrid planted in the same field and, therefore, produce grain "contaminated" with the Bt presence. Not much you can do about this.

Other pollen drift avoidance strategies

Any strategy that you develop to minimize the potential for pollen drift will be particularly useful for the south and west edges of non-GMO corn fields. This is because our prevailing winds in Indiana during the summer are from the southwest. Remember, the greater the distance between GMO and non-GMO corn fields, the less likely cross-pollination will occur.

Pollen drift risk assessment

If you are really ambitious, you can make the effort to monitor the pollination timing of your fields and adjacent fields during this coming season. Consequently, you can then rank or prioritize your non-GMO fields in terms of their likely contamination susceptibility to GMO pollen drift from adjacent fields.

For example, let's say that your field of non-GMO BinBuster 1400 begins silking on 10 July and therefore becomes susceptible to fertilization by any corn pollen in the neighborhood. As you walk and watch your neighbor's adjacent fields of Bt corn, you note that they began shedding pollen on 5 July. Given your knowledge of the pollination process, you know that there is a strong likelihood that some contamination by GMO pollen drift from those adjacent fields can still occur. If you also monitor wind direction during the pollination period, you can further refine your assessments by predicting which adjacent field is most likely to "cross over the line" in terms of pollen drift.

Harvesting, drying and storage operations

Plan to harvest all of your non-GMO hybrids first and finish with the GMO hybrids to minimize the risk of commingling of the grain in the combine and/or trucks and wagons. Similar advice can be given for soybean. You can further prioritize your corn harvest if you took pollination notes described above and ranked each field by its likely level of seed purity.

Ensure your drying and storage facilities are absolutely clean of any GMO grain possibly left over from the 1999 crop. Consider moving or selling your GMO grain directly off the farm to avoid any possibility of grain commingling in your drying and storage facilities.

Final comment

Be aware that grain buyers who limit or segregate GMO corn grain purchases this fall will have quick test kits available to them for the detection of the Bt Cry1A(b) gene in the two major Bt events in the marketplace (Monsanto Mon810 and Novartis Bt11). Other tests for other genes/events may become available by fall. For more information on these kits, look at the Web site for Strategic Diagnostics, Inc. at

Corn Growers GuidebookFor other information about corn, take a look at the Corn Growers Guidebook on the World Wide Web at

It is the policy of the Purdue Agronomy Department that all persons shall have equal opportunity and access to its programs and facilities without regard to race, color, sex, religion, national origin, age, or disability. Purdue University is an Affirmative Action employer. This material may be available in alternative formats.
© 2000, Purdue University
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