On May 13, Thomas Peters, UMN Extension sugar beet agronomist and UMN Extension IPM educator Eric Yu joined UMN Extension crops educator Angie Peltier for a discussion about the economics of preemergence herbicides. This was the inaugural episode of the 2026 UMN Extension Strategic Farming: Field Notes series of webinars.
This series of weekly programs is sponsored by the Minnesota Soybean Research & Promotion Council and the Minnesota Corn Research & Promotion Council.
The first 2026 Field Notes session discussed the value of soil residual herbicides, or those herbicides applied to the soil at seeding a cash crop. When enough rain falls within 10 to 14 days after application, soil-residual herbicides become dissolved in the soil water solution where they can be passively taken up by weed seeds. The germinating weed is killed and never emerges.
Recent research conducted by the weed science team at UMN Extension under the direction of Debalin Sarangi has revealed that some of Minnesota waterhemp populations are resistant to many of the labeled postemergence herbicide groups such as Group 2 (ex. Raptor), Group 4 (ex. XtendiMax), Group 5 (atrazine), Group 9 (ex. RoundUp PowerMax), Group 10 (ex. Liberty Ultra), Group 14 (ex. Flexstar) and Group 27 (ex. Callisto). Weed resistance usually does not occur in every field. However, it is imperative that growers are aware of resistance in their area of the state and take precautions to manage its spread. Further, this makes getting good early-season weed control using preemergence herbicides a crucial foundation for season-long weed control.
According to Peters, “the critical stage for weed control in corn is the V6-V8 stage; or when the corn plant is starting to think about kernel number. The information that I have come across has shown that the return on investment of getting good early season weed control with a soil-applied, preemergence herbicide program is greater than 100%. Return on investment is more variable for weed control in soybean but can range from break even to greater than 300%, depending on weed species and the timing of weed interference.”
