Every retailer has an opinion about glyphosate-resistant corn and its use and place in the cropping system. Dave Bell, an agronomist from Central Coop in Ellendale, MN, and Gary Spence, location manager for Crystal Valley Coop in Lake Crystal, MN, share their views.

“[Glyphosate-resistant corn] is a simple, easy-to-handle program for big growers,” Spence says. “And we're starting to see the genetics in some of the top corn hybrids.”

Spence estimates that glyphosate-resistant corn is on 65% of the corn acres in his territory, up from 35% in 2004. Bell reports that glyphosate-resistant corn acres are increasing across his area as well, moving from 5% in 2004 to 40% for 2005.

“Even growers who recognize the value of glyphosate-resistant soybeans and want to protect that system are drawn to the stacked traits containing glyphosate-resistant corn,” Spence says.

“These guys want big planters without insecticide boxes, and they're concerned with the health effects of handling soil insecticides.”

Glyphosate-resistant corn can be a good fit for tough weed control situations in some crop rotations. “It really works well in our dairy situations where we have corn and alfalfa and go four years without a row crop,” Bell says.

Despite its popularity, Spence doesn't promote glyphosate-resistant corn and soybeans in rotation, but it still happens. “We like to see growers walk before they run and try to control their glyphosate use, so we don't ruin a great herbicide for soybeans,” he says.

“We were really frustrated trying to control weeds in soybeans before glyphosate came along,” Spence continues. “We don't want to ruin a good thing through over application and cut rates.”

Both Bell and Spence recommend a preplant soil herbicide followed by a tankmix of glyphosate and a residual herbicide to carry weed control on glyphosate-resistant corn through the growing season.

“Growers can really lose yield without a preemergence herbicide on corn,” Bell stresses. “Farmers tend to get a false sense of security with the glyphosate system.”

Experts can argue about glyphosate-resistant weeds all they want, Bell says, but weed shifts are a proven result.

“We see weed shifts in woolly cupgrass and proso millet,” he adds, “while giant ragweed germination has moved from May to June through glyphosate selection.”

Even in corn-on-corn rotations, growers should be encouraged to alternate chemical modes of action.

Even though Roundup Ready corn has completed European Union approvals, retailers and growers still must understand and review their grain-channeling agreements.

“While the majority of corn in southern Minnesota goes for ethanol and animal feed use,” Spence says, “growers still need to be aware of the approved grain channels and understand the limitations imposed on trait corn, particularly when they move to stacked hybrids.”

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