I recently attended the Iowa State University Weed Science Field Day at the Curtiss Farm outside of Ames. During this field day, I noticed an area of shorter, yellow corn as compared to the surrounding corn (Figures 1 and 2). My initial thoughts were 1) this area was a wet area and probably had experienced significant denitrification, or 2) perhaps they missed applying nitrogen in this research block.
Figure 1. Shorter, yellow corn with nitrogen deficiency symptoms in the foreground due to heavy weed pressure. Image courtesy of Angie Rieck-Hinz, Iowa State University.
Figure 2. Same area as the first photo, just showing how short the corn was on July 2, 2025 as Dr. Wes Everman, Extension Weed Scientist leads the discussion at the Weed Science Field Day. Image courtesy of Angie Rieck-Hinz, Iowa State University.
When I asked the weed science program manager, who responsible for the weed science research program, he told me all the weed science plots received the same amount of nitrogen, it was all applied at the same time, and it was all the same corn hybrid.
He pointed out the difference in the corn was due to the weed pressure. The surrounding research plots had a pre-emerge herbicide application and a timely post-applied herbicide application, but this particular area did not have a pre-emerge herbicide and the weeds had accessed and used the soil nitrogen. Plus, it had an untimely or late post-application of herbicides that allowed weed growth and exacerbated the situation (Figure 3). Weeds not only compete for light, space, and water, but also nutrients. It was a fascinating observation and a good reminder of why effective weed control, both a pre- and post-application as well as effective timing are important.
Figure 3. Side-by-side comparison of the fully treated, both pre- and post-herbicide application plot on the left, compared with the plot with no pre-emerge herbicide on the right. Image courtesy of Meaghan Anderson, Iowa State University.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 21, 2025. The information contained within may not be the most current and accurate depending on when it is accessed.
- Field Agronomist in NC Iowa