Research Highlights

Using Cereal Rye Cover Crop to Boost Weed Control Without Hurting Soybean Yield

Highlights:

• Wisconsin researchers show that a cereal rye cover crop can play a key role in weed management.
• Results from a multi-year, multi-state research project shows that high amounts of cover crop biomass can suppress waterhemp and giant ragweed growth.
• When planting soybeans early, delaying cover crop termination until after planting works well for weed suppression.
• The use of a cover crop in tandem with soil residual herbicides increases the confidence for successful weed suppression.

By Rodrigo Werle and Guilherme Chudzik, University of Wisconsin-Madison Cropping Systems Weeds Science Program

Cereal rye, also known as winter rye, continues to gain traction among Wisconsin and Midwest farmers as a soil conservation crop that can also play a big role in weed management. The University of Wisconsin-Madison Cropping Systems Weeds Science program (WiscWeeds) has been evaluating fall-planted cereal rye, in collaboration with colleagues at their university and across the United States. Their question: Can cereal rye be a reliable partner in integrated weed management programs, particularly for managing troublesome weeds like waterhemp and giant ragweed?

Why Cereal Rye?

Cereal rye is a hardy, fast-growing cover crop that can survive harsh winters and produce significant spring biomass before planting soybean. When properly managed, this biomass forms a thick mulch layer that suppresses weeds by reducing light, moderating soil temperature, and creating a physical barrier to emergence⁵. Growers across the region consistently mention weed suppression and reduced soil erosion as top reasons for adopting a cereal rye¹ cover crop.

How Much Biomass Is Enough?

Our multi-year field studies in Wisconsin, funded by the Wisconsin Soybean Marketing Board, the North Central Soybean Research Program, and the United Soybean Board, have helped define how much cereal rye biomass is needed to achieve meaningful weed suppression^1,5. Research from the WiscWeeds lab shows that the required biomass depends on whether the goal is to slow weed growth or reduce overall weed emergence.

• Waterhemp: About 2,500 lbs/ac⁻¹ of dry cereal rye (~19 inches tall) biomass is enough to reduce waterhemp growth and vigor by 50%, while achieving a 50% reduction in waterhemp density, fewer seedlings emerging, requires approximately 4,500 lbs/ac⁻¹ (~33 inches tall cereal rye)⁵.
• Giant ragweed: Around 3,500 lbs/ac⁻¹ (~26 inches tall) of cereal rye biomass reduces giant ragweed growth by 50%, whereas 4,250 lbs/ac⁻¹ is needed to suppress seedling emergence by the same amount (~31 inches tall cereal rye)¹.

These results highlight that more biomass generally means better weed suppression, but growers can tailor their cover crop management depending on whether the goal is to reduce weed vigor or prevent new weed seedlings from establishing.

Timing Termination: Walking the Tightrope

One of the biggest questions we get from growers is: When should I terminate cereal rye?

Our recent multi-state study found that delaying rye termination until soybean emergence (VE–VC growth stage) strikes the best balance between maximizing biomass and protecting yield of early planted soybean. Terminating too early reduces weed suppression, while waiting too long (beyond VC or 4,500 lbs/ac⁻¹, whichever happens first) can hurt soybean stand and yield. In our early soybean planting trials in southern Wisconsin (planted around April 25th), this window equated to approximately 15 days between soybean planting and cereal rye termination.

This “planting green” approach (Figure 1), planting soybeans into living rye and terminating the cover shortly after, works best when soybeans are planted early and paired with a soil residual herbicide. Successful implementation also depends on proper planter setup and adequate soil moisture at planting. Over the years, we have found that planting soybean early, when cereal rye biomass levels are lower, is generally easier than planting later, when the cover crop has accumulated excessive biomass.

Cover Crops and Herbicides: Friends, Not Foes

A common concern is whether heavy cereal rye residue might “tie up” preemergence herbicides by intercepting the spray. Our field studies with preemergence herbicides showed that cereal rye biomass does intercept some herbicide, but early-season weed control was not reduced when using effective residual programs^3,4. This means growers can confidently use preemergence herbicides in systems that include cereal rye, especially when rainfall follows soon after to move product into the soil.

Soil Health Bonus

Beyond weed control, five years of continuous rye cover cropping at the Arlington and Lancaster ag research stations have shown measurable gains in soil carbon, organic matter, and aggregate stability compared to conventional tillage (Felsman et al. in preparation). These results confirm that the same practices helping to suppress weeds also improve soil structure and long-term productivity.

Take-Home Messages

• Aim high for biomass: At least ~3,500–4,500 lb ac⁻¹ (4–5 Mg ha⁻¹) of dry cereal rye biomass is needed for meaningful suppression of tough weeds like waterhemp and giant ragweed.
• Plant early, terminate late: Delaying cereal rye termination until soybean emergence maximized weed suppression without hurting yield of early planted soybean in our trials.
• Pair with a soil residual herbicide: Effective preemergence programs complement cereal rye’s early-season weed suppression and extend control.
• Expect added soil benefits: Long-term cereal rye adoption (>5 years) improved soil health and resilience in our trials.

Cereal rye isn’t a silver bullet, but when properly managed, it’s a powerful tool in the weed management toolbox, reducing herbicide pressure, slowing resistance development, and improving the sustainability of Wisconsin cropping systems.

References

1. Chudzik, G., Nunes, J. J., Arneson, N. J., Arneson, G., Conley, S. P., & Werle, R. (2024). Assessment of cover crop adoption and impact on weed management in Wisconsin corn-soybean cropping systems. Agrosystems, Geosciences & Environment, 7, e70007. https://doi.org/10.1002/agg2.70007

2. Chudzik, G., Nunes, J. J., Arneson, N. J., Stoltenberg, D. E., & Werle, R. (2025). Cereal rye biomass effects on giant ragweed suppression inform management decisions. Agrosystems, Geosciences & Environment, 8, e70023. https://doi.org/10.1002/agg2.70023

3. Nunes, J. J., Arneson, N. J., Wallace, J., Ruark, M., Conley, S., & Werle, R. (2023). Impact of cereal rye cover crop on the fate of preemergence herbicides flumioxazin and pyroxasulfone and control of Amaranthusspp. in soybean. Weed Science, 71(5), 493–505. https://doi.org/10.1017/wsc.2023.46

4. Nunes, J. J., Arneson, N. J., DeWerff, R. P., Ruark, M., Conley, S., & Werle, R. (2023). Planting into a living cover crop alters preemergence herbicide dynamics and can reduce soybean yield. Weed Technology, 37(3), 226–235. https://doi.org/10.1017/wet.2023.41

5. Nunes, J. J., Arneson, N. J., Smith, D., Ruark, M., Conley, S., & Werle, R. (2024). Elucidating waterhemp (Amaranthus tuberculatus) suppression from cereal rye cover crop biomass. Weed Science, 72(3), 284–295. https://doi.org/10.1017/wsc.2024.21

Additional Resources

Cereal Rye Cover Crop Termination Timing Effects on Soybean Yield Across the Midwest – SRIN article

Wisconsin Researchers Explore Cereal Rye Cover Crops for Weed Suppression – SRIN article 

Cover Crops Could be Another Weapon Against Weeds Beyond the Soil Surface – SRIN article

Cover Cropping Before Soybean – Science for Success fact sheet

Republished with permission.

The Soybean Research & Information Network (SRIN) is funded by the Soy Checkoff and the North Central Soybean Research Program. For more information about soybean research, visit the National Soybean Checkoff Research Database.

Published: Jan 26, 2026