Purdue News
Purdue News
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April 2001 To Bt or not to Bt, that is the question farmers must askWEST LAFAYETTE, Ind. – Corn growers who pass up genetically modified hybrids to plant conventional varieties this spring may be better off in the long run, say two Purdue University experts. "None of the currently available insect-resistant or herbicide-tolerant corn or soybean varieties is critical for the success of Indiana farmers," says Bob Nielsen, Purdue Cooperative Extension Service corn specialist. "Because these transgenic crop traits are not critical for Indiana farmers, the choice of whether to grow them or not depends primarily on the farmer's assessment of the uncertainty of market acceptance for such products and/or the available seed supply of alternative nontransgenic varieties." The primary pest targeted by genetically modified corn is the European corn borer. Because corn borer infestations are historically infrequent across Indiana, transgenic hybrids offer little economic advantage to most farmers, Nielsen says. Such biotech (Bt) varieties are most effective in controlling corn borer if planted very early or late in the season, he says. Selling transgenic corn could pose a greater challenge. Grain elevator operators are increasingly reluctant to accept Bt corn that does not have full approval for use in the global market, says Dirk Maier, Purdue Extension agricultural engineer. Public debate over transgenic crops intensified last fall, when the Bt hybrid StarLink corn showed up in brand name taco shells. StarLink contains Cry9C, a Bt protein unapproved – but believed safe – for human consumption. The taco shells were recalled. U.S. farmers planted 340,908 acres of StarLink corn in 2000. Only 3,564 of those acres were in Indiana, the largest concentration being in the northwestern counties of LaPorte, Starke and Marshall. Responding to the StarLink controversy, the U.S. Department of Agriculture in December strongly recommended seed companies sample and test their 2001 seed corn lots and seed parent lines for the Cry9C transgene. Any seed lot testing positive for Cry9C will be diverted to livestock feed and nonfood industrial uses. "Unfortunately, seed companies cannot guarantee zero presence of Cry9C in any seed lot," Nielsen says. "The currently available quantitative tests, when used with appropriate sampling intensities, are capable of detecting the presence of the Cry9C protein at the minimum detectable level of no less than about 0.2 percent, with a 99 percent probability." Farmers should get written verification from seed dealers that conventional varieties they're buying have been verified to be free of the Cry9C protein, Nielsen says. "Additionally, consider saving a sample of seed from each lot of supposed nontransgenic hybrid or variety for purity retesting in the event you have to reverify," he says. Farmers who planted Bt corn in 2000 are advised to plant another crop in their fields this year, Maier says. Similarly, producers should prevent transgenic "volunteer" corn from sprouting in soybean fields. Another concern is the seed mixing of conventional varieties with Bt hybrids. Growers planning to use both conventional and Bt seed should plant nontransgenic lots first, Maier says. "In this way, any seed carrying over from one seed lot to another in the planter will be from nontransgenic to transgenic and not the other direction," he says. Cross-pollination of conventional varieties by genetically modified hybrids can occur when wind carries pollen into surrounding fields. Pollen can travel a quarter mile or farther, Nielsen says. "Communication with neighbors is an important aspect of pollen drift awareness," Nielsen says. "Farmers should find out what corn hybrids will be planted adjacent to their fields of nontransgenic corn, and document the hybrid seed lot information and planting dates." Nielsen and Maier advise farmers against planting corn tolerant to glyphosate herbicides. Such hybrids are approved only in the United States and Japan. "No quick test kits currently exist for this transgene, and no tolerance levels have been established," Maier says. "Even though some grain buyers are assuring farmers that they will purchase grain from these hybrids, farmers bear the sole risk for rejection at the first point of sale should buying policies change any time in the future." Conversely, grain buyers and processors will be buying glyphosate-tolerant soybeans, Maier says. More information on transgenic crops is available in the Nielsen-Maier paper, "GMO Issues Facing Indiana Farmers in 2001." The paper is available online. Sources: Bob Nielsen, (765) 494-4802; rnielsen@purdue.edu Dirk Maier, (765) 494-1175; maier@purdue.edu Writer: Steve Leer, (765) 494-8415; sleer@aes.purdue.edu Purdue News Service: (765) 494-2096; purduenews@purdue.edu Related Web site:
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