Research Highlights

Research Highlights
Wisconsin Researchers Explore Cereal Rye Cover Crops for Weed Suppression

University of Wisconsin weed science research specialist Ryan DeWerff no-till plants soybeans into cereal rye terminated 10 days before planting on May 7, 2021. Photo: Rodrigo Werle

By Carol Brown

Weeds such as waterhemp and Palmer amaranth have evolved becoming resistant to certain herbicides, which makes them a conundrum to manage. Weed scientists no doubt have their work cut out for them to stay ahead of the game.

University of Wisconsin-Madison Assistant Professor and Weed Specialist Rodrigo Werle and his team are conducting several research projects that explore ways to control herbicide-resistant weeds, including the use of a cereal rye cover crop.

“There is growing interest in cover crops in Wisconsin and beyond and using them for weed suppression is part of that interest. Lately, we’ve been giving several talks to farmers about this topic,” Werle comments. 

The projects address questions prompted by farmers concerning cereal rye cover crop management including: how much biomass is needed for weed suppression, proper timing of cover crop termination, herbicide spray interception — how much herbicide reaches weeds through the cover crop biomass, planting green, and cover crop termination efficacy using a roller crimper. The projects are funded by the Wisconsin Soybean Marketing Board, United Soybean Board, and industry partners. 

“From a weed science aspect, the beauty of using a cereal rye cover crop is that we can see an immediate result. If you have substantial cover crop biomass accumulated (more than 4,500 pounds per acre), we see a tremendous benefit regarding weed suppression,” says Werle. “We don’t have to wait multiple years to see benefits like you do from a soil health perspective.”

How Much Cover Crop Biomass is Enough?

High amounts of cereal rye cover crop biomass (10,000 lbs/acre) can be an effective weed management tool. The photo shows reduced waterhemp growth in the area with high cereal rye biomass compared to the surrounding area without the cover crop. The study was led by Ph.D. student Jose Junior Nunes and Nick Arneson, University of Wisconsin weed science outreach program manager. Photo: Rodrigo Werle

Once a cereal rye cover crop is established, knowing how much biomass is needed to reduce weed emergence is key to its termination timing. Werle and his research team conducted a test that compared amounts of dry cereal rye biomass with weed emergence. They varied the biomass amounts on the soil surface from 500 pounds per acre up to 10,000 pounds per acre, as well as a control plot of no biomass. Then after 42 days, they measured weed growth underneath the biomass. 

In 2021, they found that approximately 7,000 pounds per acre of dry biomass was needed to reduce waterhemp plant population by 50%, but only about 700 pounds still suppressed waterhemp growth by 50%. These studies are being replicated in 2022 and results will be available for farmers. 

Planting Green

Werle is part of a USB-funded project, led by Purdue University weed scientist Bryan Young, exploring best management practices for herbicide-resistant weeds. The project is comprised of eight studies in 16 states. Werle and his team lead the component on the impact of waterhemp and Palmer amaranth suppression when planting soybeans green. Planting green means planting soybeans into living cover crops then terminating the cover crop afterward. This allows the cover crop to grow for a longer period in the spring for the most biomass accumulation, which covers the row spaces and inhibits weed establishment.

The research team is conducting the planting green portion of the USB project in 12 states on university research plots as well as in farmer fields. In Wisconsin, waterhemp density (the number of plants per square meter) was greatly reduced when soybeans were planted green compared to no-till plots and plots with cover crop termination 10 days before planting. But with the larger amounts of cereal rye biomass (beginning around 11,000 pounds per acre), soybean stands and yields were impacted, which indicates that farmers may need to weigh the trade-off between weed suppression and soybean yield. 

Figure 1. Waterhemp density at post-emergence application at 4-inch weed height. Black numbers indicate the number of days cereal rye treatments delayed post application. Delaying cereal rye termination resulted in reduced waterhemp populations and delayed post application timing. Source: Rodrigo Werle, University of Wisconsin Crop Weed Science

Termination Methods

One of Werle’s research projects is looking at cover crop termination methods. In addition to glyphosate termination, his team is measuring how effective a roller crimper is for cereal rye termination from a weed management aspect. 

“We have organic agriculture in Wisconsin and using the roller crimper is a way to terminate cover crops without using chemicals. Farmers are asking us to test the roller crimper in a conventional system as well,” explains Werle. “One of the challenges we have noted is that after crimping the rye at anthesis, or flowering, some plants would pop back up, compete with the crop and set seed.”

They found the combination of crimping followed by an application of glyphosate worked really well, especially when planting soybeans green into high amounts of rye biomass. They obtained a good soybean stand, and planting and spraying were easier to manage with the rye laying down. It’s important to note that cereal rye must be at full anthesis for effective termination with a roller crimper.

Werle’s team found that when all these elements are put together — growing large amounts of cereal rye biomass, planting soybeans into green cover, terminating the cereal rye with a roller crimper followed by a glyphosate application — they seem to provide a successful recipe for weed suppression. 

For more information about these projects and their results, go to the WiscWeeds presentation here: Weed suppression in corn-soy systems with cereal rye. The slides include summaries of each project conducted by Werle’s research team. The team is comprised of weed science specialists Nick Arneson and Ryan DeWerff; nutrient and pest management specialists Dan Smith and Kolby Grint; and graduate students Jose Junior Nunes, Jacob Felsman, and Guilherme Chudzik.

For more information about the planting green portion of the project, watch Werle’s webinar, which is part of USB’s Take Action series:

Published: Jan 2, 2023