sealPurdue News

May 2000

Protect corn crop value by protecting crop identity

WEST LAFAYETTE, Ind. – The GMO-conscious marketplace, which is causing new identity-preservation practices at planting, will require new harvest habits, too.

Purdue University Extension corn specialist Bob Nielsen says farmers may be risking future sales if they don't avoid commingling genetically modified and conventional crops when plotting, planting and harvesting.

Crops that have been genetically modified are known to farmers and others familiar with agriculture as "GM crops" or "GMO" for "genetically modified organisms." Because of protests from some consumers about genetically modified ingredients in their food, some food companies and corn and soybean processors in 1999 refused to buy genetically modified grains or paid discounted prices for them. In response, many farmers this year are segregating their genetically modified corn and soybean crops from their conventional crops.

The two most common genetically modified crops are Bt corn, which is bioengineered to produce a protein that kills the European corn borer, and soybeans that are modified to tolerate specific brands of herbicides.

Nielsen says contamination happens either when adjacent fields cross-pollinate or when seeds get mixed or commingled. "The latter can occur at planting as farmers switch from one hybrid to another in the planter," Nielsen says. "Commingling can also occur during or after harvest ,with grain mixing in the combine, trucks and wagons, drying facility, or in storage."

"Pure" conventional crops begin with the seed. Nielsen suggests that farmers get whatever assurances they can from their seed dealers on the level of purity in the seed they buy. "If your seed company will not share the exact purity levels, ask their representative to at least tell you what the company's own seed purity standards are," he says.

The corn expert also advises farmers that volunteer, or hold-over, genetically modified corn plants from the previous year's crop may sprout in conventional crop fields. To avoid that problem, he advises against planting conventional corn into last year's genetically modified field. Pollen drift from the volunteer plants can cause contamination, too, he says.

To avoid genetically modified seed carryover in the planter, plant conventional hybrids first and genetically modified hybrids last for soybeans as well as corn, Nielsen says.

Planting early maturity conventional hybrids first and later-maturing genetically modified hybrids later can reduce the risk of pollen from a genetically modified field contaminating the silks of an adjacent conventional field. While it's possible to minimize cross-pollination this way, Nielsen says it's by no means foolproof. "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," he says. "Obviously, this strategy is difficult to implement if you do not have control of the adjacent cornfields."

To protect the genetically modified and conventional crops from contaminating each other, Nielsen offers a variety of practical management strategies:

• Ensure that fields next to a conventional hybrid cornfield are also conventional crops or are planted with a different crop such as soybeans. "If the adjacent land area is wooded or grassy pastures, all the better," he says.

• If a farmer doesn't control adjacent fields or cannot negotiate with the farmers who do, he or she should plan to harvest a number of rows around the edges of the conventional field and segregate the grain to minimize the harvest-time commingling of that potentially "contaminated" grain with the grain from the rest of the field.

• Seed company agronomists indicate that genetically modified corn pollen should not contaminate more than the outside 20 rows with levels that exceed 1 percent if nothing separates the two fields. If the conventional field is bordered by a buffer zone of conventional crop about 660 feet wide, the grain from the outside 20 rows should not require segregation.

Ambitious farmers can monitor when pollination occurs in each of their fields this season in order to can rank the conventional fields based on their susceptibility to drifting genetically modified pollen from adjacent fields. "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," Nielsen says.

When harvest time arrives, Nielsen recommends that all conventional crops be harvested first to minimize the risk of commingling grain in the combine, trucks and wagons.

The same harvest advice applies for conventional and genetically modified soybeans, he says, even though pollination contamination is not an issue, because soybeans are self-pollinated.

Before the harvest, farmers should be sure that their drying and storage facilities are absolutely clean of any genetically modified grain possibly left over from the 1999 crop. "Consider moving or selling your genetically modified grain directly off the farm to avoid any possibility of grain commingling in your drying and storage facilities," Nielsen says.

Finally, Nielsen cautions farmers to be aware that grain buyers who limit or segregate their genetically modified corn grain purchases this fall will have quick test kits available for the detection of the Bt Cry1A(b) gene in the two major Bt hybrids, Monsanto Mon810 and Novartis Bt11.

Source: Bob Neilsen, (765) 494-4802,

Writer: Amy H. Raley, (765) 494-6682;

Purdue News Service: (765) 494-2096;

Related Web sites:
KingCorn, the Corn Growers' Guidebook

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