Can "planting green" suppress troublesome glyphosate tolerant/ resistant weeds in no-till soybean?

Final report for ONC21-094

Project Type: Partnership
Funds awarded in 2021: $39,680.00
Projected End Date: 03/31/2023
Grant Recipient: Stute Farms
Region: North Central
State: Wisconsin
Project Coordinator:
Dr. James Stute
Stute Farms
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Project Information


No-till (NT) and cover crops (CC) used in concert improve agricultural sustainability in our region of Southern Wisconsin by increasing crop yield when properly managed, protecting soil while enhancing soil health, protecting water quality by reducing nutrient loss and their use is socially acceptable, giving farmers “license to farm”- overall public approval from keeping the landscape green. However, difficult to control weeds which are glyphosate tolerant or resistant (GTRW) are now prevalent, threatening the combination because alternative management options include tillage or eliminating CC residue to increase residual herbicide efficacy, either of which will negate sustainability gains. We hypothesize that using winter rye as cover and managing its biomass differently than currently practiced will suppress problematic weeds, adding to CC functionality and overall sustainability.

Replicated strip-trials on 4 farms over 2 years evaluated cereal rye cover crop use/ management (planting rate and termination timing) for weed suppression compared to current Extension recommendations for management of GTRW without rye. We monitored weed dynamics throughout the growing season and impact on crop yield. We also examined the impact of rye canopy on efficacy of residual herbicide to determine if spray interception is cause for concern. We found that planting green and terminating rye at anthesis reduced GTRW populations by 94-100% compared to University of Wisconsin Extension best practice recommendations but reduced soybean yield by up to 29%. Terminating rye before soybean emergence reduced populations by 40 to 64% and was yield neutral to positive. We also surmise the practice could be an important component of resistance management to steward the new traits developed in response to resistance to glyphosate. Finally, GTRW suppression was always greater in systems with rye: if rye biomass intercepted residual herbicide reducing its efficacy, the impact was offset by rye’s suppressive effects.

Our outreach activities included a hands-on field day, interactions with highly engaged, regional farmer-led watershed groups, regional and national conference presentations, media articles and direct farmer-consultant communication through one of our projects partner farmers who is also a practicing crop consultant.

Project Objectives:
  1. Determine if rye planting rate and delayed termination i.e. “planting green” are effective for controlling/suppressing problematic GTRW in no-till soybean. Soybean is the crop of interest because this rotational phase is where the problem is greatest
  2. Compare use of cover crops against current University of Wisconsin-Extension (UWEX) herbicide recommendations for GTRW suppression
  3. Determine if rye residue from traditional, preplant termination affects efficacy of preemergence residual herbicide
  4. Determine effect of termination timing on rye aboveground biomass and soybean yields
  5. Share results and experiences with farmers and technical advisors including UWEX Weed Science.


Click linked name(s) to expand/collapse or show everyone's info
  • Tom Novak - Technical Advisor
  • Tom Burlingham
  • Tyler Troiola
  • Nick Kau


Materials and methods:

We conducted replicated on-farm strip trials during the 2021 and ’22 growing seasons near Palmyra and East Troy Wisconsin to evaluate the efficacy of rye management for suppressing GTRW compared to cooperators routine practices which follow basic University of Wisconsin-Extension (UWEX) recommendations for GTRW management.  All trial sites have long no-till histories in corn-soybean rotation and have populations of one or more of the targeted, glyphosate tolerant weed species, requiring additional management attention by the cooperator. Targeted weeds were marestail (MT), waterhemp (WH) and giant ragweed (GRW).

Our project had three basic treatment sets to meet our objectives: a no rye control; rye terminated before soybean emergence, seeded at two different rates; and, rye terminated at anthesis, seeded at the same two rates. The termination timings provide the extremes in biomass production and therefore potential impact on the cropping system.

Treatments specifics include:

  1. No rye control. This treatment followed UWEX recommendations for resistance management including complete burndown of existing weeds with glyphosate + 2,4-D (added for control of emerged GTRW) along with a preemergence (PRE) residual herbicide. Application details are provided below;
  2. Rye cover, 40 lb./a seeding rate, early termination (PRE) with the complete burndown herbicide combination and residual herbicide;
  3. Rye cover, 80 lb./a seeding rate, termination timing and herbicide identical to treatment 2;
  4. Rye cover 40 lb./a seeding rate, residual and 2,4-D burndown herbicide, termination delayed to anthesis (“planting green”); and
  5. Rye cover 80 lb./a seeding rate, termination timing and herbicide identical to treatment 4.

A sixth treatment: “routine farm practice” was included in the original trial design. In practice, cooperators followed basic UWEX recommendations with some variation in herbicide active ingredients used between farms. We standardized the product protocol and used this treatment as a duplicate control which became important for equalizing the number of observations in pooled statistical analysis where treatments were combined. 

Full burndown included glyphosate [0.75 lb. acid equivalent (AE)/a] with 2,4-D (LV formulation in 2021, choline formulation in 2022 to maintain label compliance). This combination was used on the controls and the PRE termination rye treatments, co-applied with residual herbicide (sulfentrazone + cloransulam-methyl, 6.5 oz./a). Glyphosate was withheld from the PRE mix for the late termination treatments then applied at anthesis, 0.94 lb. AE/a to endure complete termination. In-season weed control consisted of 2,4-D choline + glyphosate (0.95 and 1.0 lb. AE/a.) following weed population characterization. We chose to use the Enlist trait based on regional use prevalence and made applications with AIXR (Spraying Systems Inc, Wheaton, IL) nozzles in accordance with label requirements. Postemergence herbicide was applied 44-60 days after planting (DAP), depending on the farm and year.

Rye was established after corn grain harvest the previous fall by drilling.  Fields were selected based on presence/uniformity of GTRW. Plots were scaled at individual sites to match equipment width with length determined by populations of GTRW to ensure uniformity across all plots. Partners used their routine practices for crop management not related to treatments. Site characteristics are presented in Table 1.

Rye was sampled before termination to determine aboveground biomass (AGB) and percent canopy as estimated by fractional green canopy cover using Canopeo (Patrignani and Ochsner, 2015). AGB was sampled from 3 areas (3 rows, 2 ft of row, clipped ground level) outside of the soybean harvest rows. Biomass is reported on a dry matter basis and canopy as percent cover. Soils were concurrently sampled to a 2-foot depth in 1-foot increments to measure profile nitrate-N (PN). Profile measurements are outside the scope of the current work but were included with outside support (USDA ARS Cooperative Agreement 58-5090-7-072) to increase the utility of project results for Producer-led Watershed Protection Groups in Wisconsin.

Soybean was planted immediately before the first rye termination date or shortly after depending on the site. The second rye sampling and termination occurred at anthesis, 25-41 DAP depending on site.

Weed emergence was monitored periodically throughout the season beginning at planting. Populations of target species were measured just before postemergence herbicide application and at harvest. Individual plot counts by specie were converted to plants/acre. Areas measured (plot size) were approximately 0.125 acre for most sites, Sites 4/8 were 0.069 acre.  The smaller plot size was used to accommodate sitting of the entire trial within “patches” of giant ragweed confirmed to be glyphosate resistance by University of Wisconsin-Madison Weed Science (Dr. Rodrego Werle, personal communication). Lack of weeds in the late terminated rye treatments in 2021 led to the decision to not apply herbicide. This decision led to soybean yield impacts making discussion of yield effect more difficult but led to observations on weed control system management discussed below. Soybean yield was determined by mechanical harvest of the center two rows and reported at 13% moisture.


Statistical analysis, data presentation and use

The experimental design is a randomized complete block with 4 replicates. Data were subject to analysis of variance procedures using RStudio (ver. 2021.09.1). Count and non-normally distributed data were analyzed with Poisson regression using the best fit general linear model (glm procedure). Rye seeding rates were combined within termination timing following analysis of the subset of rye containing treatments which indicated no consistent effect of seeding rate (p≥0.065) for all response variables except preemergence AGB and % canopy. Treatments 1 and 2 were combined to create one control due to identical experimental treatment (described above) and to equalize the number of observations per treatment for the analysis. Data were analyzed over sites as well as by site to provide site specific information for cooperators and to explain interactions which may be caused by unique site conditions including preplant weed management. Data are presented by year despite no tendency for a treatment interaction to demonstrate the differences in magnitude of results produced and consistency of treatment performance across unique growing season conditions. Site 1 contributed to rye productivity data but was abandoned following a hard frost on May 29 which killed soybean in the control treatments which were not protected by rye biomass.

Rye AGB and canopy data were submitted to the UW-Madison Dept. of Soil Science for inclusion in the SnapPlus Nutrient Management (NM) Planning software database. SnapPlus is Wisconsin’s official NM planning program and uses this data to estimate soil and nutrient loss based on agronomic practices. Inclusion of more cover crop conservation performance data should improve estimates of sediment and nutrient loss reductions associated with cover use.

Site specific precipitation data was collected from local reporting stations from the Community Collaborative Rain Hail and Snow (CoCoRaHS, network. Two of the sites (WI-WW-027 and WI-JF-10) are maintained by cooperators, a third [WW-JF-15, Site 2, Palmyra (W)] was vetted for data reporting integrity before data use. All trial sites were located within one-quarter mile of a reporting station. Climate data from the NOAA National Weather Service Field Office at Sullivan, WI (, 42.96793, -88.54920) was used for current and 20-year (2000-2019) mean growing degree day (GDD) accumulation as well as 20-year precipitation means for the Palmyra area sites. Long-term data has been maintained for the East Troy sites. Precipitation data from WI-JF-10 was used to characterize the Palmyra area for the comparison to the 20-year mean (Figure 1), WI-WW-027 for East Troy.

Research results and discussion:

Growing season conditions had a major influence on crop growth and development and influenced weed suppression and soybean yield. In summary, 2021 began hot and dry, and these conditions persisted throughout the season, toggling between moderate and severe drought as classified by the National Drought Mitigation Center: US Drought Monitor ). Conditions allowed timely fieldwork, but crops were under varying degrees of moisture stress throughout the season. In contrast, 2022 began wet and cool delaying field activities, a mid-season dry period led to crop moisture stress, then an abrupt change to abundant precipitation in early August caused a rebound in crop condition and growth. Overwinter precipitation, important for early rye growth and soil moisture recharge, was approximately 73% of normal averaged across sites in both years. A summary of monthly precipitation and GDD accumulation can be found in Table 2, monthly and seasonal precipitation departures from long-term mean are presented in Figure 1.

Timely rainfall in adequate amounts is required for activation of surface applied residual herbicides. Most Midwestern University Extensions suggest between 0.5 and 1 inch are required for activation, depending on the level of soil moisture, organic matter, and texture, and are required within 7 to 10 days post application (DAA, days after application). This is consistent with the label for the product used in this study, which was applied to dry soil in 2021, moist soil in 2022.

Daily precipitation from the time of application to 45 days post-application is presented in Figure 2. Timing and amount requirements appear to be met in 2021 in both trial regions with a single event and several smaller follow-up events at all locations within 10 DAA. This is not the case in 2022 when no precipitation fell within 10 DAA and singular events exceeding the suggested 0.5 inch minimum fell well beyond 10 DAA. This data is important to the weed suppression discussion below.


Rye biomass production and canopy

Rye AGB and percent canopy at termination results are presented in Figure 3. Delaying termination from planting to anthesis increased AGB approximately 13-fold. This relationship was similar in both years despite 60-66% greater AGB levels in 2022 which most likely resulted from greater early season precipitation to support rye growth (Table 2). The increased seeding rate increased rye AGB at early termination (p ≤ 0.007) and canopy (% green cover) at both termination timings (p≤ 0.006) but not AGB at the anthesis termination (p≥ 0.148).

Percent canopy at the PRE termination timing is an important consideration for both termination timings because it represents potential residual herbicide interception during application and thus, a reduction of herbicide efficacy. Mean canopy ranged from 7.9 to 17.2% and while significant (p≤ 0.006), increasing seeding rate had a minimal impact on canopy, +2.3% in 2001, +3.6 in 2022. Canopy increased with increasing biomass, 2022 was 118% greater than 2021. Coupled with the lack of an apparent “activation” rainfall event, increased cover probably compounded already reduced herbicide efficacy.                       


GTRW suppression

Rye in combination with residual PRE-applied herbicide was more effective in GTRW suppression compared to herbicide alone (Figure 4).  The degree of suppression was strongly affected by termination timing: late termination in the planting green system producing 94 to 100% suppression compared to control across GTRW species while early, PRE termination provided 40 to 64%. This relationship was consistent across sites and apart from WH, was largely unaffected by rye seeding rate.

Marestail was present at all sites in both years and in greater numbers in 2021. This relative abundance is somewhat surprising given the precipitation received in 2021 for residual herbicide activation. More importantly, the lack of rainfall for apparent activation in 2022 may give a better indication of rye’s suppressive effect alone. While the reduction in population was highly significant (p <0.001) for both termination timings in both years, the reduction was less in 2022 (PRE, 40.0%; POST, 93.6%) compared to 2021 (64.1 and 97.9% respectively), but still substantial and indicates the value of the cover crop as part of an integrated weed management system, especially when conditions do not favor herbicide activation.

Giant ragweed and WH only occurred at single site-years each, GRW at S4 in 2021, HW at S7 in 2022 and followed similar suppression trends in both cases. The GRW reduction: PRE, 49.8%; POST 99.0% (p<0.001) is interesting, not only in absolute terms but also in the reduction in population variability which is evident in the spread of the rye treatment boxplots (Figure 4). The large spread of the no rye treatment is assumed due to the patchy nature of the weed, and is not evident in the rye treatments, indicating more consistent performance. Waterhemp suppression: PRE, 54.2%; POST, 100% (p=0.180 for PRE, POST not analyzed statistically due to complete suppression, all zero values) in 2022 occurred in the year with questionable residual herbicide activation, therefore we believe this suppression is mostly due to rye/ rye residue. This is also the only case where seeding rate had an unquestioned (p<0.001) effect on suppression, 26.6 vs 81.8% (40 vs. 80 lb./ acre respectively), further supporting the rye/ rye residue suppression argument.

The concern over rye biomass interception of soil-applied residual herbicide leading to reduced efficacy also appears unwarranted, at least under the conditions of this study. This observation is based on the consistent reduction from the herbicide only treatment to the early terminated rye treatment: better system performance regardless of interception. Further evidence is provided by the lack of seeding rate influence on suppression. In the PRE termination timing, the greater rye seeding rate increased both AGB and percent canopy, both indicators of potential herbicide interception, yet little difference in weed population was observed (WH at S7 is the exception for seeding rate influence but occurred in the year of questionable activation).

Lack of weeds in the late terminated rye treatments led to the decision not to apply post emergence herbicide in 2021, a systems level decision based on the principals of integrated pest management (IPM). This resulted in significantly greater marestail populations (p=0.008) from later emerging plants at harvest in this treatment and is partially responsible for soybean yield reduction (Figure 5). Because marestail populations did not rebound after POST herbicide application in the no rye and early termination treatments relative to the late termination treatment, we conclude a post application “flush” did not occur, thus the suppression provided by the late termination timing delayed the in-season flush. In a year with adequate moisture, we would anticipate a second flush of marestail following application, necessitating a second herbicide application. The practical implication of this observation is that suppression by late rye termination may result in the need for only one post emergence herbicide application in years with adequate moisture, reducing both chemical control costs and the potential for resistance development by subjecting fewer weeds to less active ingredient. In review, we should have delayed the POST herbicide application in the late-terminated treatments for a more objective comparison.


Soybean yield

Soybean yield is presented in Figure 5. Yield response to rye management followed the same pattern in both years: equivalent to slightly increased yield for PRE termination relative to no rye and a significant (p<0.001) yield reduction for late termination. The yield reduction is mostly attributed to direct competition for moisture and additional moisture stress during a season-long drought (2021, 28.8% reduction) or midseason drought (2022, 15.1% reduction). Secondary contributors could include shading and mechanical interference from standing rye (Figure 6), especially in 2022 with greater AGB levels (Figure 2). Figure 7, Figure 8 show developmental differences at different times of the growing season. The 2021 late-season marestail flush in the untreated POST treatment presumably also contributed although the population was relatively low at harvest (810 plants/a) and conversely, these soybean plants were not subject to the additional stress of herbicide exposure for during the mid-season application.

In general, plants grown in the late termination system were smaller than either other treatment and exhibited moisture stress sooner as soils dried following rain. This treatment demonstrated compensatory growth as precipitation began to exceed normal in mid-2022 and plants were similar in size and appearance to the other treatments at maturity. In general, the timely rains in mid-2022 resulted in yields which are considered good in this region.


What the data doesn’t show   

The following observations deserve mention but don’t necessarily fit neatly in the above categories:

The delayed termination treatment delayed maturity by approximately 7 days across all sites (based on maturity ratings) and resulted in greater (~2%) grain moisture at harvest. Delayed maturity is evident in Figure 9.

Rye residue in the delayed termination treatment remained standing by harvest at some locations (Figure 10). While not possible in an experimental situation, combine adjustment may be necessary to manage the additional material flowing through the combine and to obtain a clean sample.

All rye treatments reduced pressure of late emerging grass weeds (crab and witchgrass, Figure 11) which are prevalent on the lighter soils of our study region. Cooperating farmers made this observation and note this may eliminate the need for a late-season application of a residual grass herbicide, reducing production costs.

Figure 12 depicts a giant ragweed plant which survived the post emergence application of 2,4-D choline and glyphosate at Site 4 in 2021. This was the first ever post emergence application of this herbicide combination to traited soybean at this site and follow-up investigation could find no fault with the application. The plant was mistakenly destroyed: it should have been submitted to the University of Wisconsin for further resistance investigation as the population has already been confirmed resistant to three other herbicide modes of action.

This finding reinforces the potential of cereal rye use as a component of a resistance management plan. Both termination timings provided substantial population reductions. In addition, the delay in weed emergence caused by late termination may make complete control possible with one postemergence application. We only needed one application during this study but in years with more favorable precipitation causing more, prolonged weed emergence, multiple control applications are often required. Fewer weeds with less herbicide active ingredient exposure is a cornerstone of resistance management. 


Profile nitrate

Soil profile nitrate-N was measured at both rye termination timings in 2021 to validate additional ecosystem services from the cover crop. Early terminated rye had no effect on PN compared to no rye, while late terminated rye significantly reduced it (Figure 13). Interestingly, PN increased significantly without rye in the ~40-day period between sampling/ termination while remaining unchanged with rye which captured PN as it became available. The increase in PN is probably the result of nitrification of residual applied N from 2020. While not measured, the potential for carryover of ammoniacal-N from 2020 corn fertilization exists because lack of moisture limited corn yield. Because these soils are leaching prone and moisture limited soybean yield (and presumably nutrient uptake), this nitrogen scavenging may have reduced leaching potential.

These results, coupled with evidence of weed suppression further support the multi-functional role of rye cover crops in creating a more sustainable agriculture.








Participation Summary
4 Farmers participating in research

Educational & Outreach Activities

2 Consultations
1 Curricula, factsheets or educational tools
2 Published press articles, newsletters
3 Tours
13 Webinars / talks / presentations
2 Workshop field days
2 Other educational activities: Two on-demand conference presentation recordings (2022 National Strip-Till Conference, 2023 National No-Till Conference) were made available by Lessiter Media and archived by NCR SARE, links available in this report.

Participation Summary:

1,230 Farmers participated
418 Ag professionals participated
Education/outreach description:

Outreach efforts included a planned field day, invited presentations and distribution of project results/ lessons learned through media. We produced a 2-page research summary for use in current and future outreach and are preparing a manuscript for publication of results in Agronomy Journal.

Our project field day was held August 12, 2022, at Langmanor Farm, Palmyra, co-sponsored by the Jefferson County Soil Builders, a newly formed Producer-led Watershed Production group whose membership includes all our cooperating farmers. Participants learned of project results to date and had an opportunity to visit one of the projects field sites. Participants also interacted with Dr. Rodrigo Werle and Nick Arneson, University of Wisconsin-Extension Weed Specialists who shared results of their work with cereal rye management for managing problematic weeds. In addition to farmers, the 46 participants included Extension educators, agency personnel and a local elected official. Unfortunately, a planned evaluation could not be administered due to a planning flaw which allowed participants to scatter following the plot tour.

Invited presentations:


National Strip-Till Conference (NSTC), Iowa City, IA (7/28/2022), 45 participants.

(A SARE Farmer Forum presentation, recorded for further distribution, link included in this report);


National No-Till Conference (NNTC), St. Louis, MO (1/11/2023), 595 participants.

(A SARE Farmer Forum presentation, recorded for further distribution, link recorded in this report);


Fox River Summit, Burlington, WI (3/16/2023), 160 participants.


Virtual Events

National Cover Crop Summit (NCCS), March 14, 2023, 250 participants


Grow Farmer Forum: Cover crop termination, March 29, 2023, 85 participants.


Producer-led Watershed Protection Group (PLWPG) events

Walworth County Soil Health/ Cover Crop Interest Group meeting, Elkhorn, WI (3/16/2022), 41 participants;


Jefferson County Soil Builders Twilight Meeting, Palmyra, WI (6/2/2022), 46 participants;


Farmers on the Rock Annual Meeting, Janesville, WI (3/17/2023), 60 participants;


Walworth County Soil Health/ Cover Crop Interest Group meeting, Elkhorn, WI (3/22/2023), 32 participants.


Miscellaneous Presentations

Byron Seeds Cover Crop Update Meetings (Loganville, WI, 2/16/2022; Waupun, WI, 3/9/2022), 142 participants;


Wisconsin Cover Crop Research and Outreach Project (CCrop) Summer meeting, Sauk Prairie, WI (6/15/2022), 45 participants;


Strategies for Land Management Summit, Lake Geneva, WI (6/21/2022), 64 participants;


Wisconsin Association of Professional Crop Consultants (WAPAC) winter meeting, Manitowoc, WI (12/8/2022), 28 participants;


Waukesha County Green Team winter meeting, Oconomowoc, WI (2/13/2023), 32 participants;



Media Distribution

Video recordings of NSTC and NNTC presentations were made available for on-demand viewing on Lessiter Media’s respective conference webpages. In addition, the NNTC recording was included in the registration package for the National Cover Crop Summit. As of this report, 443 total views included 130 on-demand for the stand-alone version and 313 for the NCCS package.


Print and electronic distribution by Lessiter Media in No-Till Farmer includes two articles:

Digital: Beat glyphosate-resistant weeds by planting green

posted 10/21/22


Print version: Using cover crops, planting green to suppress glyphosate resistant weeds

Digital version: On-farm trials show cover crops, planting green can suppress weeds

Scheduled publication date: July 17, 2023



Learning Outcomes

4 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • The magnitude of GTRW suppression, regardless of termination timing.

  • The negative impact of late termination on soybean yield. At the time we initiated this project, the soil health "evangelists" were advocating late termination solely based on biomass yield potential without considering weed suppression or yield impacts. While the soil health goal is laudable, the recommendation may have led new users to have bad outcomes, potentially dissuading them from continued cover crop use. This project provided data to weigh benefits and tradeoffs.

  • Related weed suppression topics: rye weed suppression offsets the effect of canopy spray interception and potential reduction of residual herbicide efficacy; use of rye can suppress late-emerging grasses regardless of termination timing, potentially reducing late-season herbicide use.

Project Outcomes

2 Grants received that built upon this project

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.