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College of Food, Agricultural, and Environmental Sciences


Glyphosate-Resistant Corn Hybrids Create Planting Challenges

May 18, 2007

COLUMBUS, Ohio -- The increased planting of Round-Up Ready corn and other transgenics that are glyphosate-resistant is creating challenges for growers who need to kill a failed corn stand before replanting.


"Killing a failed corn stand for the purposes of replanting corn used to be pretty straightforward. Apply glyphosate to the failed corn, and plant the new corn stand. Or, plant the new corn stand and then apply glyphosate to the failed stand before the new corn emerges," said Mark Loux, an Ohio State University Extension weed specialist. "However, killing the failed stand has become somewhat more complicated in fields where Round-Up Ready corn was planted initially."

When using glyphosate is not an option, the alternatives can get complicated, and in some cases, more expensive. Time is also working against the grower when it comes to replanting.

"A grower can get his corn in by April 15 and then realize on May 10 that his stands failed," said Loux. "He has to get that second stand going quickly. Every day counts with planting corn when you run the risk of losing a bushel a day after the optimum planting date."

The following are several options for the control of Round-Up Ready corn in replanting situations:

• The most effective treatment is the use of Select Max. Loux said that it is inexpensive (around $5 per acre), but at least a five-day waiting period to plant corn is required after application to avoid plant injury and problems in stand establishment. "Ohio Department of Agriculture obtained a Section 18 Crisis Exemption label for use of Select Max to control failed stands of Round-Up Ready corn. That temporary label is valid until May 24," said Loux.

• A mixture of Gramoxone Inteon and metribuzin is the best option when it is not possible to wait five days to replant. "However, for reasons we don't know, metribuzin is in short supply this year, so it may be difficult to secure that ingredient to make the application effective," said Loux. "This treatment is effective in corn less than 5 inches tall."

• Application of Gramoxone Inteon alone, or an application of Liberty, can also be effective. But according to Ohio State University research and studies conducted at other land-grant universities, treatment was less effective on corn higher than three inches. "We were able to obtain near complete control of corn treated at the 3-inch stage, but control was generally less effective when treating 11-inch corn," said Loux.

For additional information on applicable treatments of failed corn stands, refer to the Ohio State University Agronomic Crops Team Web site at

Planting conventional corn hybrids is becoming less of an option for growers, especially as transgenics -- Bt corn, stacked traits -- become more popular. According to the U.S. Department of Agriculture, 13 percent of Ohio's corn planted last year was herbicide-resistant. It is estimated that nearly half of Ohio's corn acreage will be planted with Round-Up Ready corn this year.

Transgenics is the science of introducing a gene from one organism or plant into the genome of another organism or plant. In crop production, Bt corn to control European corn borer and rootworm, and Round-Up Ready corn and soybeans for enhanced weed control would be examples of transgenics.

"Round-Up Ready soybeans helped to increase the popularity of Round-Up Ready corn," said Loux. "Round-Up Ready corn has now become a big part of a seed company's offerings. I wouldn't be surprised to see 80 percent to 90 percent of our corn acreage Round-Up Ready in the next few years."

The convenience of seed packages, low cost and higher yields compared to conventional hybrids are also sparking an interest in the use of Round-Up Ready corn.

Loux said increasing use of Round-Up Ready corn will create challenges for growers when managing glyphosate, but ongoing research on new herbicides and technology may offer additional options in the future.

Corn is one of Ohio's most valuable field crop commodities, second to soybeans in acreage and economic value. According to the Ohio Department of Agriculture, corn production contributes $836 million to agriculture.


Candace Pollock
Mark Loux