On May 13th, 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 pre-emergence herbicides. This was the inaugural episode of the 2026 UMN Extension Strategic Farming: Field Notes series of webinars.
This series of weekly programs has a different, timely crop production topic each week. This program runs from 8:00 to 8:30 am each Wednesday morning through at least August 12, through the generous support of the farm families of 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 I have found indicates that the return on investment for good early-season weed control with a soil-applied, pre-emergence herbicide program exceeds 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.”
Eric Yu suggests that there are two critical things to consider adopting to both preserve a preemergence herbicide’s efficacy long term and get the best value out of a preemergence herbicide program: 1) use the full label rate of pre-emergence herbicides, and 2) use preemergence herbicides from two different herbicide groups at a time. “We can achieve nearly 100% control when we use the full rate of at least two different sites of action,” shares Yu. Coming preemergence herbicides from site of action 14 and 15 are most common in corn and soybean production in Minnesota.
While the session lasted only 30 minutes, it was full of useful, actionable information. For those who missed this session, it is now available to listen to on your favorite podcasting platform.
