The Wisconsin Cropping Systems Weed Science Program has been conducting extensive research on soybean “planting green” system as part of integrated weed management strategies.
Our field research demonstrates that planting green and terminating cereal rye when it reaches approximately 30–36 inches in height (~4,500 lbs of biomass per acre) or at the soybean VE stage, whichever occurs first, is a promising approach for suppressing weeds without negatively impacting soybean yield (Guilherme Chudzik’s PhD research). However, we have also consistently observed that soil-applied residual herbicides are still necessary, even in high-biomass cereal rye systems, to achieve effective early-season control of troublesome weeds such as waterhemp (Nunes et al. 2024).
Farmer in southern Wisconsin planting soybean green (picture taken May 07 2025).
A common question from stakeholders across Wisconsin and beyond is:
Which soil residual herbicides are compatible with high-biomass cereal rye cover crop systems?
In other words, which herbicides are most likely to move through the cereal rye residue layer and reach the soil where they can be effective?
To address this, WiscWeeds students and staff Lukas Holderby, Sabeel Abuhakmeh, and Dr. Ahmad Mobli conducted a controlled-environment study this winter evaluating 21 single-active-ingredient corn and/or soybean herbicides. This study assumed adequate precipitation following application and simulated a condition of ~4,500 lbs of dry cereal rye per acre on soil surface; future research will evaluate how rainfall patterns influence herbicide movement through cover crop residue.
Simulated application of soil-residual herbicides in a high-biomass (4,500 lb/acre) cereal rye system.
Lukas Holderby, Sabeel Abuhakmeh, and Dr. Ahmad Mobli harvesting a controlled-environment study at UW-Madison Walnut Street Greenhouse evaluating soil-residual herbicide performance in high-biomass cereal rye systems. Twenty-one single–active-ingredient corn and/or soybean herbicides were assessed for waterhemp control; not all products were equally effective or compatible with high cover crop biomass. This image highlights the mission of the WiscWeeds Lab: delivering timely, research-based recommendations while training the next generation of agricultural professionals.
Corn herbicides identified as effective for waterhemp control AND compatible with high-biomass cereal rye in this study included:
- Acetochlor (Harness – Group 15)
- Dimethenamid-P (Outlook – Group 15)
- Pyroxasulfone (Zidua – Group 15)
- S-metolachlor (Dual II Magnum – Group 15)
- Atrazine (Group 5)*
- Isoxaflutole (Balance Flexx – Group 27)
- Mesotrione (Callisto – Group 27)
*waterhemp population used in this study is still susceptible to atrazine applied preemergence.
Soybean herbicides identified as effective for waterhemp control AND compatible with high-biomass cereal rye in this study included:
- Dimethenamid-P (Outlook – Group 15)
- Pyroxasulfone (Zidua – Group 15)
- S-metolachlor (Dual II Magnum – Group 15)
- Flumioxazin (Valor – Group 14)
- Fomesafen (Flexstar – Group 14)
- Metribuzin (Group 5)
Soybean growers should pay close attention to application timing restrictions. Flumioxazin-containing products for instance must be applied within three days of soybean planting, while metribuzin must be applied prior to soybean emergence. The remaining herbicides can be applied preemergence or early postemergence, offering flexibility for growers who plant early and delay cereal rye termination until after soybean emergence.
A standard program in planting green systems where the cereal rye is terminated after soybean emergence may include glyphosate for cereal rye termination, combined with soil residual herbicides fomesafen plus a Group 15 herbicide (e.g., pyroxasulfone, S-metolachlor, or dimethenamid-P) and a Group 2 herbicide such as imazethapyr (Pursuit), cloransulam (FirstRate), or chlorimuron (Classic) for broad spectrum weed control.
Example of a herbicide treatment identified as effective for waterhemp control AND compatible with high-biomass cereal rye in this study:
Versus example of a herbicide treatment not identified as effective for waterhemp control nor compatible with high-biomass cereal rye in this study*:
*note higher waterhemp density in the cereal rye residue treatments.
While these findings are preliminary and additional controlled-environment and field research is ongoing, we aim to provide timely guidance to help growers make informed decisions as the 2026 planting season approaches.
The use of multiple effective soil-residual herbicides at higher labeled rates in tandem with high cereal rye cover crop biomass is strongly recommended to achieve more consistent early-season weed control and to reduce selection pressure for further herbicide resistance.
This research project was conducted by WiscWeeds Team Members Lukas Holderby, Sabeel Abuhakmeh, and Dr. Ahmad Mobli. This overall effort is being funded by the Wisconsin Soybean Marketing Board, United Soybean Board, and USDA-NIFA.
Research Update Article written by Dr. Rodrigo Werle, UW-Madison Extension Cropping Systems Weed Scientist.
