January 15, 2025

Looking for a way to help herbicides control problem pigweeds such as waterhemp and Palmer amaranth? Plant green.
Recently published research in the journal Weed Science shows how teaming preemergence herbicides with planting soybeans over a cereal rye cover crop can pair soybean production with pigweed suppression.
“Our findings support the premise that planting soybean green is an effective recommendation to optimize cereal rye biomass production for effective waterhemp and Palmer amaranth suppression,” says Rodrigo Werle, a University of Wisconsin Extension cropping systems weed scientist and a contributing author to the journal article. “Integrating an effective preemergence herbicide program at soybean planting was also an important component of effective Amaranthus species control.”
Planting green provides more time for cereal rye to grow and produce biomass to suppress weeds without interfering with timely planting when compared with cover crop termination one to two weeks before soybean planting. Besides suppressing weeds, cover crops such as cereal rye contribute to:
Reduced soil erosion
Increased soil organic matter
Improved biological soil health
How to make the system work
The newly reported research findings come from 10 U.S. states (Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Missouri, North Dakota, Pennsylvania and Wisconsin) during the 2021 and 2022 growing seasons.
“It is evident from our findings that the planting green system can effectively optimize cereal rye biomass production and improve weed suppression,” Werle says. “Yet, soybean response to planting green can vary, with some studies reporting no effect on yield and some studies reporting some yield reduction.”
Attention to detail when planting green is essential to optimize soybean stand establishment and, thus, yield in this system.
“Soybean stand was a key factor in maintaining soybean yields compared to no-till when planting green,” Werle says. “Farmers should follow best management recommendations for proper planter and equipment setup to ensure effective soybean establishment under high levels of cereal rye biomass when planting green. Enough soil moisture is also critical for planting green success.”
As herbicide-resistant waterhemp and Palmer amaranth populations in multiple U.S. states increase, nonchemical weed-control methods, such as cover cropping, are gaining interest and popularity as an alternative weed-management strategy. This study shows that pairing cover crops with preemergence herbicides provides an even greater benefit than either practice does alone.
“Planting soybean green provided a 44% reduction in Amaranthus species density compared to no-till,” Werle says. “The use of preemergence herbicides resulted in a 68% reduction in Amaranthus species density compared to no preemergence. So, overall, we found that planting soybean green is a feasible management practice to optimize cereal rye biomass production, which, combined with preemergence herbicides, provided effective Amaranthus species management.”
Editor’s note: The Weed Science Society of America provided the information for this story. More information about planting soybean green and Amaranthus species weed control can be found here in Volume 72, Issue 5 of Weed Science, a Weed Science Society of America journal. This multistate collaborative study, sponsored by the United Soybean Board, was led by Jose Junior Nunes, a former doctoral student in Werle’s Cropping Systems Weed Science Research & Extension lab.
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