Finding the sweet spot: rye termination timing to balance weed suppression and yield reduction in green planted no-till soybean.

View the project final report

Commodities

• Agronomic: soybeans

Practices

• Crop Production: cover crops, no-till
• Education and Training: farmer to farmer, participatory research
• Pest Management: cultural control

Glyphosate tolerant/ resistant weeds (GTRW: marestail, waterhemp and giant ragweed) are a daunting, widespread problem in no-till systems. Our previous SARE work (Project ONC21-094) in Wisconsin demonstrates that a late terminated cereal rye cover crop can provide highly effective GTRW suppression in “green planted” no-till soybean but has the potential to reduce yield to unacceptable levels. Our objective is to determine the optimum timing of rye termination in this system to maximize GTRW suppression without affecting yield. Our overall intent is to use rye as part of a resistance management strategy while also achieving soil conservation and health benefits.

We conducted on-farm  trials during the 2023-24 growing  seasons at four locations in Southeast Wisconsin over a range on soil types and environments including inherent GTRW pressure to determine this optimum timing or “sweet spot”, evaluating preplant (PP) termination along with weekly termination beginning at soybean emergence (VE) through rye anthesis which corresponded to soybean growth stage V3. We used residual herbicide on all treatments which included control of emerged weeds. We measured weed suppression, the percent reduction in weed population density from the no rye control at time of first post emergence herbicide application as well as yield. We also measured rye aboveground biomass (AGB) at each termination. We experienced contrasting growing season conditions which helped illuminate the relationships between termination timing, rye AGB, weed suppression and yield.

We found that PP termination resulted in 41 to 82% suppression, the level of which was determined by rye AGB.  We also found an average yield increase of 1.7% compared to no rye and in combination, these two results continue to make a compelling case for use of rye as a cover crop. Delaying termination resulted in increased suppression in a nonlinear fashion with substantial gains not occurring until the later termination timings where we achieved suppression levels of 88 to 95%. Soybean yield declined with delayed termination and the rate was determined by growing season precipitation. In a drought year, the rate of yield decline was more rapid, and we experienced a 26.5% yield loss with anthesis termination. Here, rye needed to be terminated before planting to protect yield. In a wet year, the rate of yield decline was lower, and we experienced no to a 9% yield loss. Here there was no penalty for planting green, but rye needed termination by soybean emergence to protect yield. Because our results point to the need for early termination for yield protection and that suppression was dependent on rye AGB, we recommend actively managing rye for maximum biomass before planting.

Our outreach activities focused on well attended producer-led group events and use of media to maximize dissemination of results and lessons learned. We who advise farmers or other professionals have incorporated project findings in our work.

1. Determine the optimal timing of rye termination in a “plant green” system to maximize GTRW suppression without reducing soybean yield;
2. Determine if rye height or soybean growth stage is a better predictor of optimal termination timing, allowing us to develop management recommendations; and
3. Share results and experiences with farmers and their technical advisors including the University of Wisconsin-Extension Weed Science Program so they can leverage our results in their routine programming.