Early Weeds Can Clip Corn Yields

Plan strategy complete with back up plans.

Published on: Apr 11, 2011

University research is not always conclusive, sometimes from year to year at the same institution, often from institution to institution across the Midwest. When universities agree, it's worth taking notes. Based on findings within the past couple of years, clear data has emerged showing that early weed competition in corn can cut yield later.

One year ago in the Indiana Prairie Farmer/ Precision Planting plots to study changes in seeding depth, downforce pressure on planting units and planting speed, weeds got a head start because of the weather. Heavy rains fell within a week of planting. Weather had already delayed planting, and it occurred the last week of May.

Pete Illingsworth, part of the farm crew at the Throckmorton Research Farm near Romney where the plot was located, sprayed the tall corn at the very end of June with Ignite. It was Liberty Link corn. Even he wasn't sure what type of results to expect. Throckmorton Research Farm is part of the Purdue University Extension farm system.

The results were amazing. He literally wiped out the weeds. Even where corn was damaged by saturated soils and grass was as high as four-leaf corn in late June, nearly all the grass was wiped out. This example became a story in Indiana Prairie Farmer, as an example of what can be accomplished if you follow label directions, include the materials the label specifies, and do a good job of spraying.

Also the weather cooperated. Very little rain fell there during July, August and September. By harvest nearly all the plots were weed-free, with not even remnants of weeds left in most cases. The plot average was in the 190 to 195 bushel per acre range, even with treatments that held down yield, and the late planting date.

What this article didn't intend to do was hold this up as the way to approach weed control. When asked how to handle these kinds of situations in the future, and why it worked, Purdue weed specialist Bill Johnson said, "Pray a lot an hope fro luck. You were lucky."

Several companies are emphasizing residual herbicide problems with preemerge applications to provide control of those early weeds should you get caught in that type of situation. Some of these products can also be applied up to 11 inch corn. In some cases, companies are pushing the two pass system, with residual laid down first and glyphosate post, and a backup plan of glyphosate plus the residual early post if weather prevents the residual application.

The bottom line is that early weeds hurt yield. Science says so. Even in our plots last year, we can't say it didn't, although yields were higher than expected for planting date. We didn't have a check where weeds were controlled early, or not controlled at all.

Work with your local chemical supplier to develop a strategy and backup plan to help you control weeds in corn this season.