Preemergence Herbicide Injury on Early Planted Soybean

New research from the University of Illinois Herbicide Evaluation Group indicates that while certain preemergence herbicides can cause early-season damage to early-planted soybeans, the crop’s yield is generally unaffected as long as adequate stand counts are maintained.

Under the direction of Extension Weed Scientist Aaron Hager, U of I Research Specialist Logan Miller has been investigating potential issues with herbicide premixes and pre-plant herbicides used on early-planted soybeans. The study evaluated soybeans planted at early dates, between April 15 and April 18, compared to conventional dates around May 15 to May 18. For plots in western Illinois last spring (2025), the early planting date was pushed to March 26.

The research addressed concerns that longer emergence times in early-planted, stressful environments could increase seedling exposure to herbicides, potentially leading to higher injury and stand loss. Miller noted that weather is a primary limiting factor, as excessive rainfall can put additional stress on the crop early in the season.

Key findings from the herbicide evaluation include:

• * PPO-based premixes (Group 14 herbicides) are the most likely to cause noticeable crop injury.
• * Authority-based products, Fierce-based products, and Zidua Pro resulted in the greatest amount of early-season crop injury and stunting.
• * Some PPO herbicides performed better than others; Prefix and Preview showed hardly any injury relative to the non-treated control.
• * Trials evaluating dry metribuzin at robust rates of 10.5 to 12 ounces showed no crop response or damage.

The study also evaluated Ilevo seed treatments, which yielded inconsistent effects on stand loss and yield across the different years of the study.

Despite the varying levels of early-season crop injury and some stand reduction from PPO herbicides, the final yield data did not show a negative effect. Miller concluded that as long as a uniform stand of 80,000 to 100,000 seeds per acre is maintained, there is little evidence of a yield impact.

This research is funded by the Illinois Soybean Checkoff. To learn more about this study, a webinar and podcast titled “Which PRE Herbicides Increase Injury Risk in Early-Planted Soybeans” are available at the ISA’s FieldAdvisor.org website.

Editor’s note: This article was adapted from a radio broadcast script and formatted for print with the assistance of Google’s generative AI tool, Gemini and has been reviewed by the primary source.