To Bt or not to Bt, that is the question

WEST LAFAYETTE, Ind. – Corn growers who pass up genetically modified hybrids to plant conventional varieties this spring may be better off in the long run.

None of the currently available insect-resistant or herbicide-tolerant corn or soybean varieties is critical for the success of Ohio or Indiana farmers, according to Bob Nielsen, Purdue Cooperative Extension Service corn specialist.

“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 the Eastern Corn Belt, transgenic hybrids offer little economic advantage to most farmers, Nielsen said.

Such biotech (Bt) varieties are most effective in controlling corn borer if planted very early or late in the season, he said.

Big question mark.

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, said Dirk Maier, Purdue 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 for human consumption.

In December, the USDA 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 will be diverted to livestock feed and nonfood, industrial uses.

“Unfortunately, seed companies cannot guarantee zero presence of Cry9C in any seed lot,” Nielsen said.

He said the currently available quantitative tests, when used with appropriate sampling intensities, can detect the presence of the Cry9C protein at the minimum detectable level of no less than about 0.2 percent, with a 99 percent probability.

Get it in writing. 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 said.

“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.”

Farmers who planted Bt corn in 2000 are advised to plant another crop in their fields this year, Maier said. Similarly, producers should prevent transgenic “volunteer” corn from sprouting in soybean fields.

Plant nonBt first.

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 said.

“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 said.

Pollination concerns. Cross-pollination of conventional varieties by genetically modified hybrids can occur when wind carries pollen into surrounding fields.

Nielsen recommends farmers 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.

Farmers are advised against planting corn tolerant to glyphosate herbicides. It is approved only in the United States and Japan. Grain buyers and processors will be buying glysophate-tolerant soybeans, Maier said.