Planting Green Into Cover Crops? Learn Which Soil Residual Herbicides Can Make it to the Ground!

By Rodrigo Werle

The Wisconsin Cropping Systems Weed Science Program has been conducting extensive research on soybean “planting green” systems as part of integrated weed management strategies.

Our field research, which is part of a USB-funded multi-state project, 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 (as found in UW-Madison graduate student Guilherme Chudzik’s Ph.D. 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, according to research by UW-Madison graduate student Jose Nunes.

“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,” said Dr. Rodrigo Werle, University of Wisconsin-Madison

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.)