Using a residual herbicide with the Roundup Ready Corn 2 System offers the best approach for achieving effective weed control and maximizing yield potential, according to a Michigan State University study.

The study, conducted by Michigan State University weed specialist Dr. Jim Kells, supports using tillage or a burn-down herbicide application, followed by a residual herbicide for early weed control and an over-the-top post application of a labeled Roundup agricultural herbicide for season-long weed control.

"The use of residual herbicides is an effective way to reduce potential yield loss if you can't be timely with your postemergence herbicide applications," says Dr. Jim Kells. "Putting a preplant or preemergence residual down can also help address potential weed-resistance issues."

Farmers planting Roundup Ready Corn 2 can use the Roundup Ready Rate of a residual herbicide. In the Michigan State study, a tank mix of acetochlor and atrazine was used for the residual treatment.

"When you're controlling weeds in field crops such as corn, your objective isn't to kill weeds," Kells explains. "Your objective is to preserve crop yield for that particular growing season, as well as to preserve crop yield for the following season by preventing the current season's weeds from going to seed."

The study also showed that, in addition to the benefits of using a residual herbicide in Roundup Ready Corn 2, the timing of postemergence over-the-top applications of glyphosate is critical.

Timing is Key

"Any delay in glyphosate applications after weeds reach four inches in height means that you run a significant risk of yield loss," Kells says. "For effective weed control, you should make the first glyphosate application when weeds are two- to four-inches tall, then follow if necessary with a second application 12 to 14 days later. The second over-the-top herbicide treatment can be glyphosate or another herbicide."

Kells' study confirms that a single application of glyphosate alone will not provide season-long weed control. "In our study, all single glyphosate applications, regardless of when they were timed, resulted in a yield loss of at least nine percent."

"Having a preemergence residual herbicide applied in Roundup Ready Corn 2, even though it means two trips across the field, will minimize yield loss to early-season weeds, and it takes some of the pressure off of being timely with your postemergence over-the-top herbicide applications," Kells says.
Roundup Ready Corn 2 is expected to be planted on approximately 50 million acres this season.