A large percentage of corn growers are no-tilling their corn, and many made the switch with the introduction of Roundup Ready herbicide-resistant hybrids. But as more acres have been identified to be infested with glyphosate-resistant weeds, the progressive no-tillers have realized they need to rotate or include different mode of action herbicides with glyphosate.

Some agronomists have suggested losing glyphosate effectiveness almost ends the potential for no-till production of corn and soybeans on fields with more than one resistant weed species. Luckily, to limit the weed resistance potential, new herbicides have been coming onto the market that can work in concert with glyphosate or relegate glyphosate to less of the workhorse herbicide.

Keith Oglesby, crop and seed specialist with Southern FS at the Eldorado, Ill., office, agrees with the opinion that glyphosate use in corn production will eventually become the new atrazine. "You have some resistance to atrazine, but it is cheap, therefore, we put it in the mix along with other herbicides to get the full spectrum of weeds, including the ones that the atrazine would miss. It provides another mode of action. This could be how glyphosate will be used," he said.

As Shawn Koehler, Bayer CropScience crop marketing coordinator, said, "One thing that no-tillers definitely have to be concerned about is glyphosate weed resistance. Respecting the rotation of alternating herbicide chemistries absolutely has to be top of mind."

Koehler went on to suggest that sustainability of notilling will been incredibly more difficult without the efficacy of glyphosate. This comes from an employee of a company that has several herbicide products that have a strong fit into no-till corn production such as Balance Flexx, Corvus, Capreno, Laudis and Ignite herbicides. Oglesby noted that of the estimated 60 percent of corn grown under no-till practices in the 12 counties served by Southern FS, there are basically three different concepts of weed control. He suggested about 25 percent are using a pre-plant burndown of glyphosate, 2,4-D and a "single-pass product" like Corvus. These growers then hope to have season-long weed control without any other investment.

Another 25 percent of no-till growers like to use a split application approach with a pre-plant residual herbicide up front at less than full rate and then a second partial rate of residual herbicide when the corn is about eight inches tall.

The remaining approximately 50 percent of growers, which includes the Roundup Ready corn growers, like to use glyphosate and a "set-up rate" of a pre-plant herbicide and some atrazine prior to planting. They plant and when the corn is eight to 10 inches tall, they make an application of glyphosate with atrazine.

As weed resistance has not yet been identified as a major issue in the Southern FS territory, quite a bit of glyphosate continues to be used, but Oglesby makes recommendations that include many different modes of action, again to preserve the effectiveness of glyphosate. The recommendation and use of pre-emerge herbicides ahead of soybeans rather than relying on glyphosate alone is also why weed resistance is still minimal in his territory, Oglesby believes.

He suggested that Corvus is a good example of a onepass product for multiple mode of action weed control in corn production. "I think the biggest thing it has going for it is the low use rate (5.6 ounces in his territory) and the multiple modes of action because you have a grasscontrol component, a broadleaf weed-control component and you can add some atrazine if wanted for a three modes of action mix."

For more information about no-till corn production options, contact Shawn Koehler at shawn.koehler@bayercropscience.com.