Results of a long-term evaluation of five weed control systems in northern Illinois indicate that yield is the major difference rather than the actual amount of effective weed control.

At the Northern Illinois Agronomy Research Center in Shabbona, Ill., a 5-year study has compared residual and non-residual herbicide systems with both Roundup Ready corn and soybeans. In this study, researchers looked at five weed control systems:

1. Pre-emergence.

2. Pre-emergence followed by a post with a residual.

3. Pre-emergence followed by a post without a residual.

4. Post only with a residual.

5. Post only without a residual.

The objective of the study was to determine how long herbicide-resistant corn and soybeans can tolerate weeds and what is the best time to remove weeds to maximize your no-till yields. Other goals in the trial include determining if a one-pass or two-pass herbicide application system is your best weed control bet and deciding on the value of applying a pre-emergence herbicide with the Roundup Ready cropping system.

“For corn, there was very little difference in weed control comparing these programs, but looking at the yields is where we saw a significant difference,” says Dawn Nordby, a University of Illinois graduate student. “The post-only programs don’t maintain the yields that we get from a pre and post or an early post, late post combination.”

Get Weeds Early

To protect your no-till corn yields, Nordby says, you should remove weeds when they are 2 to 4 inches tall, about at the V4 stage.

…