Introduction
Palmer amaranth and sicklepod are among the most challenging to control and economically damaging weed species in peanut production systems across the southeastern United States (Daramola et al. Reference Daramola, Iboyi, MacDonald, Kanissery, Singh, Tillman and Devkota2023; Everman et al. Reference Everman, Burke, Clewis, Thomas and Wilcut2008). These species aggressively compete with peanut growth, leading to significant reductions in peanut yield and harvest operation efficiency (Daramola et al. Reference Daramola, Iboyi, MacDonald, Kanissery, Tillman, Singh and Devkota2024a, Reference Daramola, MacDonald, Kanissery, Tillman, Singh, Ajani and Devkota2024b; Johnson and Luo et al. Reference Johnson and Luo2019). Managing these weeds in peanut crops is particularly challenging due to their high seed production, prolonged emergence periods, and limited availability of effective herbicide options (Everman et al. Reference Everman, Burke, Clewis, Thomas and Wilcut2008; Mahoney et al. Reference Mahoney, Jordan, Hare, Leon, Roma-Burgos, Vann, Jennings, Everman and Cahoon2021). As of 2024, 131 cases of herbicide resistance across 12 different weed species have been confirmed in the United States (Heap Reference Heap2025). Among these weeds, Palmer amaranth is regarded as one of the most difficult to manage in peanut systems, having evolved resistance to nine different herbicide sites of action (Heap Reference Heap2025). Controlling sicklepod is also challenging, because it belongs to the same botanical family as peanut, limiting the availability of selective herbicide options.
Historically, peanut growers in the United States have relied on intensive tillage systems to establish residue-free seedbeds (Price et al. Reference Price, Reeves, Patterson, Gamble, Balkcom, Arriaga and Monks2007). However, rising production costs and growing concerns about soil health have sparked interest in conservation tillage practices that minimize soil disturbance (Godsey et al. Reference Godsey, Vitale, Mulder, Armstrong, Damicone, Jackson and Suehs2011). Although conservation tillage offers soil and environmental benefits, it often leads to greater dependence on herbicides for weed management due to limited mechanical options, thereby increasing the risk for the development of herbicide-resistant weeds (Dentzman and Burke Reference Dentzman and Burke2021; Van Deynze et al. Reference Van Deynze, Swinton and Hennessy2022). Furthermore, the growing prevalence of herbicide-resistant weeds has imposed significant challenges on conservation tillage systems, leading to poor weed management and a resurgence in tillage (Beckie Reference Beckie2014; Kumar et al. Reference Kumar, Mishra, Rao, Mondal, Hazra, Choudhary, Hans and Bhatt2020; Price et al. Reference Price, Balkcom, Culpepper, Kelton, Nichols and Schomberg2011).
In the past two decades, the use of cover crops to diversify cropping and weed management systems has grown steadily and become more popular in the southeastern United States (Deines et al. Reference Deines, Guan, Lopez, Zhou, White, Wang and Lobell2023). Between 2012 and 2017, the cover-cropped area in the United States increased by 50%, from approximately 4 million ha to 6 million ha, with projections estimating expansion to 40 million ha in 2025 (Hamilton et al. Reference Hamilton, Mortensen and Allen2017). Fall-planted cover crops have been shown to benefit agronomic cropping systems by improving soil quality and water infiltration, reducing nutrient leaching, increasing soil organic matter, conserving soil moisture, sequestering organic carbon, and providing early season weed suppression (Essman et al. Reference Essman, Loux, Lindsey, Dobbels and Regnier2020; Silva and Bagavathiannan Reference Silva and Bagavathiannan2022). Cereal rye is the predominant winter cover crop among growers in the southeastern United States due to its winter hardiness and potential for high biomass production (SARE 2007; Silva and Bagavathiannan Reference Silva and Bagavathiannan2022). The weed-suppressive effects of cereal rye are primarily attributed to the release of allelochemicals and the physical barrier created by its residue biomass, which inhibits weed seed germination and growth by modifying the quality and intensity of light reaching the soil surface (Blackshaw et al. Reference Blackshaw, Moyer, Doram and Boswell2001; Teasdale and Mohler Reference Teasdale and Mohler2000). However, the level of weed suppression from cereal rye residue has been shown to vary with management practices and geographic location (Osipitan et al. Reference Osipitan, Dille, Assefa and Knezevic2018; Silva and Bagavathiannan, Reference Silva and Bagavathiannan2022).
Management practices related to the establishment and termination of cereal rye are important for optimizing biomass production and weed suppression, with termination timing exerting the greatest influence (Boselli et al. Reference Boselli, Anders, Fiorini, Ganimede, Faccini, Marocco, Schulz and Tabaglio2021; Mirsky et al. Reference Mirsky, Spargo, Curran, Reberg-Horton, Ryan, Schomberg and Ackroyd2017). For example, Mirsky et al. (Reference Mirsky, Spargo, Curran, Reberg-Horton, Ryan, Schomberg and Ackroyd2017) demonstrated that termination timing has a stronger influence on cereal rye biomass accumulation than planting date. Specifically, a delay in termination by just 10 d resulted in a biomass increase by an average of 2,000 kg ha−1, whereas achieving a similar increase required planting the cover crop 45 d earlier. Delayed cereal rye termination has been shown to provide superior weed suppression relative to early termination in several row crops, including corn (Balkcom et al. Reference Balkcom, Duzy, Kornecki and Price2015; Carrera et al. Reference Carrera, Abdul-Baki and Teasdale2004, DeSimini et al. Reference DeSimini, Gibson, Armstrong, Zimmer, Maia and Johnson2020), cotton (Price et al. Reference Price, Monks, Culpepper, Duzy, Kelton, Marshall, Steckel, Sosnoskie and Nichols2016; Saini et al. Reference Saini, Price, Van Santen, Arriaga, Balkcom and Raper2018; Wiggins et al. Reference Wiggins, Hayes and Steckel2016, Reference Wiggins, Hayes, Nichols and Steckel2017), and soybean (Essman et al. Reference Essman, Loux, Lindsey and Dobbels2023; Nunes et al. Reference Nunes, Arneson, DeWerff, Ruark, Conley, Smith and Werle2023; Palhano et al. Reference Palhano, Norsworthy and Barber2018; Wiggins et al. Reference Wiggins, Hayes, Nichols and Steckel2017). Additionally, integrating herbicides with rye termination has shown promise for improving weed control (Carrera et al. Reference Carrera, Abdul-Baki and Teasdale2004; Nunes et al. Reference Nunes, Arneson, DeWerff, Ruark, Conley, Smith and Werle2023; Price et al. Reference Price, Monks, Culpepper, Duzy, Kelton, Marshall, Steckel, Sosnoskie and Nichols2016). However, to our knowledge, no published research has examined the combined effects of cereal rye termination timing and herbicide programs on weed management in peanut crops. Existing studies of weed control in peanut production have focused on a single termination timing (Aulakh et al. Reference Aulakh, Saini, Price, Faircloth, van Santen, Wehtje and Kelton2015; Dobrow et al. Reference Dobrow, Ferrell, Faircloth, MacDonald, Brecke and Erickson2011; Lassiter et al. Reference Lassiter, Jordan, Wilkerson, Shew and Brandenburg2011; Price et al. Reference Price, Reeves, Patterson, Gamble, Balkcom, Arriaga and Monks2007). While delayed termination can enhance biomass accumulation and weed suppression, excessive residue may hinder peanut stand establishment, increase interception of residual herbicides, and potentially reduce their efficacy (Nunes et al. Reference Nunes, Arneson, DeWerff, Ruark, Conley, Smith and Werle2023). Furthermore, residue management techniques such as the use of a roller-crimper to flatten desiccated cereal rye into a surface mulch or planting directly into standing residue may also influence weed suppression and peanut crop response. Standing residue can reduce soil erosion and moisture loss but may obstruct planting equipment (Torbert et al. Reference Torbert, Ingram and Prior2007). In contrast, rolled cereal rye forms a uniform mulch that enhances weed suppression but may increase preemergence herbicide interception, reduce soil evaporation, and lower soil strength compared to standing residue (Ashford and Reeves Reference Ashford and Reeves2003; Kornecki et al. Reference Kornecki, Price, Raper, Arriaga and Schwab2009). Therefore, a balance must be achieved between maximizing cereal rye biomass for weed suppression and managing surface residue to minimize negative impacts on peanut production. Thus, the objective of this study was to evaluate the interactions among cereal rye termination timing, residue management strategy, and herbicide program intensity on weed control in peanut crops.
Materials and Methods
Description of Experimental Site
Field experiments were conducted during the 2022–2023 and 2023–2024 growing seasons at the West Florida Research and Education Center, in Jay, Florida (30.776542°N, 87.147662°W; 62 m elevation), using separate fields each year. For 1 yr before the studies began the study site had remained in a natural weedy fallow state, with no chemical or tillage weed control. Soil at the site was classified as a Red Bay Fine sandy loam with 2.1% organic matter, pH 5.6. Sicklepod was the dominant weed species present in both years. To ensure consistent weed pressure, sicklepod and Palmer amaranth seeds collected from a previous study in 2021 were broadcast at rates of 300 seeds m−2 and 500 seeds m−2, respectively, in mid-November each year.
Experimental Design and Treatments
The experiment was arranged in a randomized complete block design with a split-plot layout and four replications. Each subplot measured 3.6 by 9.1 m, and each main plot consisted of four subplots, resulting in a total main plot size of 14.4 by 9.1 m. The main plot treatments were the combination of cereal rye termination timing and residue management, which included 1) early termination 28 d before peanut planting (DBP) with cereal rye residue left standing; 2) early termination 28 DBP with cereal rye residue rolled flat; 3) late termination 14 DBP with cereal rye residue left standing; 4) late termination 14 d DBP with cereal rye residue rolled flat; and 5) no-till control without cereal rye cover crop. The subplot treatments were herbicide program intensity (Table 1), which consisted of four treatments: 1) an intensive program including preemergence, early postemergence, and mid-postemergence applications; 2) a reduced program that excluded preemergence herbicides; 3) a reduced program that excluded early postemergence herbicides; and 4) a nontreated control. Herbicides were applied at 1, 30, and 60 d after peanut planting (DAP) for preemergence, early postemergence, and mid-postemergence timings, respectively (Table 2).
Table 1. Herbicides evaluated for their effects on cereal rye termination timing and residue management.
a Brake®; SePRO, Carmel, IN (0.16 kg ai ha−1).
b Gramoxone® SL 3.0; Syngenta Crop Protection, LLC, Greensboro, NC (0.25 kg ai ha−1).
c Dual Magnum®; Syngenta, Crop Protection (1.33 kg ai ha−1).
d Basagran®; Winfield Solutions, Research Triangle Park, NC (0.33 kg ai ha−1).
e Cadre®; BASF, Corporation, Durham, NC (0.07 kg ai ha−1).
f Outlook®; BASF (0.02 kg ai ha−1).
g Butyric 200®; Winfield Solutions (0.25 kg ai ha−1).
h Storm®; United Phosphorus Inc., King of Prussia, PA (0.25 kg ai ha−1).
i Valor® SX; Valent U.S.A. Corporation, Walnut Creek, CA (0.06 kg ai ha−1).
jltra Blazer®; United Phosphorus Inc. (0.25 kg ai ha−1).
Table 2. Dates of field activities and treatments.
Crop Management
Prior to cereal rye planting, paraquat (Gramoxone SL 2.0; 1.1 kg ai ha−1; Syngenta Crop Protection, Greensboro, NC) was applied to control emerged vegetation. Cereal rye (Secale cereale L. ‘Wrens Abruzzi’) was sown as a winter cover crop in mid-November preceding each trial using a no-till drill (1206 NT; Great Plains, Salina, KS) at a rate of 65 kg ha−1, with 2.6-cm seeding depth and 19-cm row spacing. Cereal rye was terminated at either 28 DBP (early termination) or 14 DBP (late termination) using glyphosate (Roundup PowerMAX; Bayer Crop Science, St. Louis, MO) applied at 1 kg ae ha−1 plus ammonium sulfate at 1.1 kg ae ha−1 for each timing. At the early and late termination timings, cereal rye growth corresponded to Zadoks stages Z51 and Z61, representing heading to mid-anthesis (Zadoks et al. Reference Zadocks, Chang and Konzak1974). Desiccated cereal rye in the rolled treatment plots was flattened in a single pass using a 3.2-m (10.5-ft; four-row) tractor-mounted roller-crimper (I&J Manufacturing LLC, Gordonville, PA) 1 DBP, oriented in the same direction as planting. Peanut cultivar Georgia 12-Y was planted in single rows spaced 91 cm apart at 154 kg ha−1 using a John Deere 1720 Max Emerge no-till planter (Deere & Company, Moline, IL), on May 15, 2023, and May 1, 2024. Herbicide treatments were applied in spray solution at 140 L ha−1 using a CO2-pressurized backpack sprayer (TeeJet Technologies, Glendale Heights, IL). All treatments were applied with a 3.6-m boom fitted with eight TeeJet TTI11002 nozzles at an application speed of 4.8 km h−1.
Data Collection
Data were collected on cereal rye biomass, weed control, and peanut yield. Prior to chemical termination, aboveground cereal rye biomass was collected from two 0.5-m2 quadrats randomly placed within each plot by clipping cereal rye at the soil surface to assess the effect of termination timing on biomass production. Harvested samples were oven-dried at 60 C for 72 h to quantify dry biomass and reported as dry weight in kg ha−1. Weed density and biomass were evaluated at three growth stages corresponding to 28 d after each herbicide application: 28 d after the preemergence application (early season), 28 d after the early postemergence application (mid-season), and 28 d after the mid-postemergence application (late season). Weed density was determined by counting the number of emerged weeds from two randomly positioned 0.5-m² quadrats located between the middle rows of each plot. Plants within each quadrat were cut at ground level for sampling and placed in a dryer set at 60 C for 72 h, after which their dry weight was measured and recorded. Peanut plants were dug using a conventional digger-shaker-inverter and allowed to air-dry in the field for 3 to 5 d; cereal rye biomass did not interfere with digging or harvesting operations. Peanut yield, reported in kilograms per hectare (kg ha−1) was adjusted to a standard moisture level of 10.5%, following the procedure described by Mulvaney and Devkota (Reference Mulvaney and Devkota2020).
Statistical Analysis
The data were analyzed using the GLIMMIX procedure with SAS software (v.9.4; SAS Institute Inc, 2012). Preliminary analyses considered all response variables with year included as a fixed effect. The explanatory variables included year, timing of termination, residue management strategies, and herbicide treatments. Interactions between year and treatment were assessed. If interactions were significant (P < 0.05), results were reported separately for 2023 and 2024; otherwise, data for both years were pooled for further analysis. In the combined analysis, termination timing and residue management (the main plot factor), herbicide program (the subplot factor), and their interactions, were treated as fixed effects. To account for the split-plot design, year, replications (blocks) nested within year, and main plots nested within replications within year, were specified as random effects. Before conducting ANOVA, data sets were evaluated for homogeneity of error variance. Square-root transformations were applied as necessary to improve normality and model fit. Treatment means were separated using Tukey’s honestly significant difference test at P ≤ 0.05. Where appropriate, data were back-transformed for reporting purposes.
Results and Discussion
Cereal Rye Biomass Production
Cereal rye biomass production differed across years and termination timings. In 2023, biomass production ranged from 6,400 to 7,350 kg ha−1, which was higher than in 2024 (6,080 to 6,800 kg ha−1; Figure 1). Delaying termination from 28 to 14 days after peanut planting (DPP) increased cereal rye biomass by 15% in 2023 and 12% in 2024, with growth advancing from Z51 (beginning of heading) to Z61 (anthesis), a stage at which biomass accumulation is generally near its seasonal maximum. These increases were likely driven by greater growing degree day (GDD) accumulation between planting and termination in 2023 (GDD 2,437 to 2,710) compared to 2024 (GDD 2,066 to 2,319; Table 3), with late termination providing an additional 342 to 391 GDDs compared to early termination in both years. Accumulated GDD is a major factor influencing biomass production, and delayed termination has been shown to enhance heat unit accumulation and cereal rye biomass production (Essman et al. Reference Essman, Loux, Lindsey and Dobbels2023; Ficks et al. Reference Ficks, Karsten and Wallace2023; Haramoto and Pearce Reference Haramoto and Pearce2019; Mirsky et al. Reference Mirsky, Curran, Mortensen, Ryan and Shumway2011). For each 10-d increase, Mirsky et al. (Reference Mirsky, Curran, Mortensen, Ryan and Shumway2011) observed an approximate gain of 2,000 kg ha−1 in cereal rye biomass. Previous studies have indicated that biomass levels exceeding 5,000 kg ha−1 are typically required for effective weed suppression (Nichols et al. Reference Nichols, English, Carlson, Gailans and Liebman2020; Norsworthy et al. Reference Norsworthy, McClelland, Griffith and Bangarwa2018). In the current study, regardless of termination timing, cereal rye biomass production surpassed this threshold.
Figure 1. Cereal rye biomass production at early and late termination timings in 2023 and 2024.
Table 3. Weather conditions at the West Florida Research and Education Center during the experiment period in 2022–2024. a
a Weather data from 2007 to 2023 were obtained from the Florida Automatic Weather Network.
b Soil temperatures were taken at a depth of 5 cm.
c Growing degree days, base 4.4 C (Mirsky et al. Reference Mirsky, Curran, Mortensen, Ryan and Shumway2011), were calculated from seeding to termination date.
Early Season Weed Density
Treatment-by-year interactions were not significant (P = 0.1) for early-season Palmer amaranth density; therefore, data were combined for both years for analysis. A significant interaction was observed between cereal rye termination management and preemergence herbicide treatments for Palmer amaranth (P < 0.001) and sicklepod density (P < 0.001) at 28 d after preemergence application (Table 4). Palmer amaranth density was reduced by 30% to 85% in plots with cereal rye cover crop compared to winter fallow, supporting previous findings that cereal rye can provide effective early season suppression of Palmer amaranth (Hodgekiss et al. Reference Hodgskiss, Young, Armstrong and Johnson2021; Nunes et al. Reference Nunes, Arneson, DeWerff, Ruark, Conley, Smith and Werle2023; Price et al. Reference Price, Monks, Culpepper, Duzy, Kelton, Marshall, Steckel, Sosnoskie and Nichols2016; Vollmer et al. Reference Vollmer, VanGessel, Johnson and Scott2020; Wells et al. Reference Wells, Reberg-Horton, Smith and Grossman2013). The high level of suppression observed in this study is likely due to high cereal rye biomass accumulation. Wells et al. (Reference Wells, Reberg-Horton, Smith and Grossman2013) reported approximately 75% Palmer amaranth control with only about 4,500 kg ha−1 of cereal rye biomass. In this study, cereal rye biomass production exceeded that threshold regardless of termination timing (Figure 1). However, no significant difference in Palmer amaranth density was observed between standing and rolled cereal rye residue, indicating that weed suppression was not solely due to physical mulch cover, but may also involve altered light conditions and microenvironmental factors from standing cereal rye residue (Menalled et al. Reference Menalled, Adeux, Cordeau, Smith, Mirsky and Ryan2022).
Table 4. Effect of cereal rye termination management and herbicide program interaction on weed density at 28 d after preemergence herbicide application, averaged over 2 yr, 2023 and 2024 a .
a Means within a column followed by a different letter are significantly different at α ≤ 0.05. Standard errors are presented in parentheses
Late cereal rye termination, whether rolled or left standing, resulted in greater reductions in Palmer amaranth density compared to early termination (Table 4). Early cereal rye termination (28 DBP), whether rolled or standing, and without preemergence herbicides, resulted in a 36% to 48% reduction in Palmer amaranth density. In contrast, Palmer amaranth density was reduced by 64% to 70% without preemergence herbicides relative to the winter fallow control at 28 d after preemergence application. The greater suppression of Palmer amaranth with late cereal rye termination is attributed to greater biomass accumulation at the later termination timing (Figure 1), which was more resistant to decomposition and likely created a more effective, long-lasting physical barrier that inhibited germination, emergence, and establishment of Palmer amaranth. This result is consistent with previous research in other cropping systems. For instance, Hodgskiss et al. (Reference Hodgskiss, Young, Armstrong and Johnson2021) reported that cereal rye terminated at or after soybean planting accumulated 40% more biomass and enhanced suppression of waterhemp [Amaranthus tuberculatus (Moq.)] compared with cereal rye termination before planting. Similarly, Vollmer et al. (Reference Vollmer, VanGessel, Johnson and Scott2020) found that cereal rye terminated 10 d before soybean planting improved Palmer amaranth control by 6% compared with termination 20 d before planting.
Palmer amaranth density under late cereal rye termination without preemergence herbicide application (11 plants m−2) was comparable to that observed in winter fallow plots treated with preemergence herbicides (13 plants m−2; Table 4). Hence, in addition to a greater Palmer amaranth suppression compared with early termination, late termination of cereal rye was as effective as a preemergence application of fluridone or flumioxazin in suppressing Palmer amaranth in this study. Nunes et al. (Reference Nunes, Arneson, DeWerff, Ruark, Conley, Smith and Werle2023) similarly observed that cereal rye cover provided effective early season suppression of Amaranthus spp. similar to that of flumioxazin and pyroxasulfone applied to soybean. Likewise, Cornelius and Bradley (Reference Cornelius and Bradley2017) reported that cereal rye residue provided a similar level of waterhemp suppression compared to a preemergence application of sulfentrazone. Therefore, our results support previous research demonstrating the effectiveness of cereal rye residue in managing Palmer amaranth. However, weed suppression by cereal rye is closely linked to biomass accumulation and ground cover, both of which are highly variable and influenced by climatic conditions and management practices (Silva and Bagavathiannan Reference Silva and Bagavathiannan2022). Under low biomass production conditions (e.g., 2,500 kg ha−1), cereal rye has been shown to provide insufficient suppression of Palmer amaranth in peanut systems (Dobrow et al. Reference Dobrow, Ferrell, Faircloth, MacDonald, Brecke and Erickson2011). Furthermore, not all weed species respond uniformly to cereal rye–based suppression (Lowry and Brainard Reference Lowry and Brainard2019; Teasdale et al. Reference Teasdale, Beste and Potts1991). Therefore, cereal rye should be viewed as a component of an integrated weed management approach rather than a stand-alone alternative to preemergence herbicides for early season weed suppression.
Differences in sicklepod density between cereal rye termination timings (early vs. late) were observed only in the absence of a preemergence herbicide application (Table 4). Without preemergence herbicides, sicklepod density was 47% to 50% lower in the late termination treatments, whether cereal rye was rolled or left standing, compared to winter fallow. Sicklepod density did not differ between early cereal rye termination treatments (rolled or left standing) and the winter-fallow control in the absence of preemergence herbicides. Only when cereal rye termination was delayed until 14 DPP did biomass accumulation become sufficient to reduce sicklepod density compared to the winter fallow control without preemergence herbicides. The lack of suppression with early termination may be attributed to the ability of large-seeded weed species such as sicklepod to emerge through mulch layers, as well as their reduced light requirement for germination (Mirsky et al. Reference Mirsky, Curran, Mortensen, Ryan and Shumway2011; Pittman et al. Reference Pittman, Barney and Flessner2020). Previous studies have shown that the need for light to trigger germination decreases as the seed mass increases (Milberg et al. Reference Milberg, Andersson and Thompson2000), which may explain the minimal impact of cereal rye residue on sicklepod. Our findings are consistent with previous research indicating that large-seeded weeds are generally less affected by cover crop residue (Vollmer et al. Reference Vollmer, VanGessel, Johnson and Scott2020).
No significant differences in sicklepod density were observed among cereal rye termination treatments and winter fallow when preemergence herbicides, either fluridone or flumioxazin, were applied. This suggest that cereal rye residue presence did not compromise early season residual control of sicklepod. Although cover crop mulch has the potential to intercept herbicide sprays, this effect appeared negligible in this study, likely due to sufficient rainfall following herbicide application. Rain of at least 9 mm occurred within 1 to 4 d after preemergence treatment in both years, which may have facilitated herbicide activation and movement into the soil. This suggests that under adequate postapplication rainfall conditions, preemergence herbicides applied in the presence of cereal rye residue can remain effective in reducing weed density. Nunes et al. (Reference Nunes, Arneson, DeWerff, Ruark, Conley, Smith and Werle2023) similarly reported that the presence of cereal rye residue did not affect the early season efficacy of flumioxazin or pyroxasulfone in soybeans, even though the concentrations of herbicides were reduced in the soil. Haramoto and Pearce (Reference Haramoto and Pearce2019) also found that the effectiveness of sulfentrazone + carfentrazone-ethyl, was not negatively affected by the presence of cover crop residues.
Mid-Season Weed Density
As with early season weed control, year-by-treatment interactions were not significant (P = 0.3) for mid-season assessments; therefore, data were pooled for both years. A significant interaction (P < 0.001) between cereal rye termination management and herbicide program was observed for mid-season weed density (Table 5). In the absence of cereal rye residue, the combination of preemergence and early postemergence herbicides reduced Palmer amaranth and sicklepod densities by 75% and 70%, respectively, compared to the early postemergence-only program. However, when cereal rye residue was present, no significant differences in weed density were detected among herbicide programs, regardless of termination management. These results suggest that in systems that include a cereal rye cover crop, a more intensive herbicide program may not be necessary to achieve effective mid-season suppression of Palmer amaranth and sicklepod. The cereal rye mulch appeared to provide suppression that was comparable to that of preemergence herbicides prior to early postemergence application, highlighting the additive benefit of cereal rye cover crop in integrated weed management system. These results further support the potential of cereal rye cover crop to complement, or in some cases replace, the weed suppression achieved with preemergence herbicides, depending on weed seedbank density.
Table 5. Effect of cereal rye termination management and herbicide program interaction on mid-season weed density at 28 d after early postemergence herbicide application, averaged over 2 yr, 2023 and 2024.a–e
a Abbreviations: EPOST, early postemergence; PRE, preemergence.
b Means within a column followed by a different letter are significantly different at α ≤ 0.05. Standard errors are presented in parentheses
c PRE + EPOST indicates a PRE application of fluridone followed by an EPOST application of paraquat + S-metolachlor + bentazon at 30 d after planting.
d PRE only indicates a PRE application of flumioxazin.
e EPOST only indicates an EPOST application of imazapic + dimethenamid-P + 2,4-DB at 30 d after planting.
The preemergence-only herbicide trial resulted in four to seven more Palmer amaranth plants per square meter and four to 10 more sicklepod plants per square meter compared to the preemergence + early postemergence treatment, across cereal rye termination management treatments. These results indicate that cereal rye residue alone is insufficient to eliminate the need for early postemergence herbicides to achieve optimal weed suppression. While cereal rye residue can provide effective control early in the season, its gradual degradation allows later-emerging weeds to establish (Mirsky et al. Reference Mirsky, Curran, Mortensen, Ryan and Shumway2011). This finding is consistent with previous studies demonstrating that cereal rye residue alone rarely provides season-long weed suppression (Osipitan et al. Reference Osipitan, Dille, Assefa and Knezevic2018; Schramski et al. Reference Schramski, Sprague and Renner2021), highlighting the importance of timely early postemergence herbicide applications. In the current study, when cereal rye was planted, application of early postemergence herbicides alone resulted in a 57% to 71% reduction in sicklepod density compared to cereal rye treated with preemergence herbicides only. When cereal rye has been terminated late, rolled cereal rye reduced sicklepod density by 43% more than standing rye when only preemergence herbicides were used, likely due to reduction in light and physical barrier.
Late-Season Weed Density and Biomass
Interactions between year and treatments were not significant for late-season Palmer amaranth and sicklepod densities or biomass (P > 0.05); therefore, data were pooled for both years. No significant interaction was observed between cereal rye termination management and herbicide program for either species (P > 0.05). At 28 d after mid-postemergence herbicide application, the presence of cereal rye residue did not significantly affect sicklepod density (P = 0.1), regardless of termination management (Table 6). In contrast, Palmer amaranth density was 40% to 53% lower in treatments that included cereal rye compared to the winter fallow control. The lack of cereal rye residue effect on late-season sicklepod density may be attributed to the progressive decomposition of cereal rye mulch over the season and the ability of sicklepod to emerge through decomposing residue. Unlike Palmer amaranth, large-seeded weed species such as sicklepod (seed weight 23–28 mg) possess sufficient seed reserves to produce elongated shoots capable of penetrating dense mulch layers (Clay and Griffin Reference Clay and Griffin2000; Leishman and Westoby Reference Leishman and Westoby1994). Despite differences in density responses, both Palmer amaranth and sicklepod exhibited significantly reduced biomass in cereal rye treatments compared with the winter fallow control (Table 6). Across herbicide programs, treatments that included cereal rye reduced late-season Palmer amaranth biomass by 63% to 67% and sicklepod biomass by 63% to 65% compared with programs that did not include cereal rye. These results align with those of Pittman et al. (2019), who reported that cereal rye cover crop with 7,671 kg ha−1 of biomass reduced horseweed [Conyza canadensis (L.) Cronquist] biomass by 50% at soybean harvest. However, the results contrast with findings by Price et al. (Reference Price, Reeves, Patterson, Gamble, Balkcom, Arriaga and Monks2007), who reported that a cereal rye biomass of 6,550 kg ha−1 did not persist long enough to significantly reduce weed biomass later in the season in a high-residue conservation-tillage peanut production system.
Table 6. Effect of cereal rye termination management and herbicide programs on late-season weed density and biomass at 28 d after mid-postemergence herbicide application, averaged over 2 yr, 2023 and 2024a–e.
a Abbreviations: EPOST, early postemergence; MPOST, mid-postemergence; PRE, preemergence.
b Means within a column followed by a different letter are significantly different at α ≤ 0.05. Standard errors are presented in parentheses.
c PRE + EPOST + MPOST indicates a PRE application of fluridone followed by an EPOST application of paraquat + S-metolachlor + bentazon at 30 d after planting followed by an MPOST application of imazapic + dimethenamid-P + 2,4-DB at 60 d after planting.
d PRE + MPOST indicates a PRE application of flumioxazin followed by an MPOST application of acifluorfen + dimethenamid-P + 2,4-DB at 60 d after planting.
e EPOST + MPOST indicates an EPOST application of imazapic + dimethenamid-P + 2,4-DB followed by an MPOST application of premixed bentazon + acifluorfen + S-metolachlor + 2,4-DB.
At 28 d after mid-postemergence herbicide application, Palmer amaranth and sicklepod densities and biomass did not differ between the preemergence + early postemergence + mid-postemergence program and the early postemergence + mid-postemergence program (Table 1). Both of these herbicide programs provided at least 43% and 44% greater reductions in Palmer amaranth and sicklepod densities, respectively, compared to the preemergence (flumioxazin) + mid-postemergence (acifluorfen + dimethenamid-P + 2,4-DB) program. Similarly, the preemergence + early postemergence + mid-postemergence and early postemergence + mid-postemergence programs reduced Palmer amaranth and sicklepod biomass by at least 36% and 15%, respectively, relative to the preemergence + mid-postemergence program (Table 6). These results indicate that residual herbicides alone are insufficient to maximize control of Palmer amaranth and sicklepod in peanut production systems. Due to the rapid growth and prolonged emergence periods of these weed species, timely early postemergence applications are critical to target small, susceptible weed cohorts, regardless of the presence of a cereal rye cover crop.
Peanut Yield
Peanut yield was significantly affected by cereal rye termination management (P = 0.03), herbicide program (P = 0.01), and their interaction (P < 0.001). In the absence of herbicide application, standing cereal rye residue reduced yield by 14% to 17% compared to the winter fallow control, regardless of termination timing. In contrast, peanut yield increased by 15% to 23% relative to the untreated winter fallow control when rolled cereal rye residue remained (Table 7). These yield gains are likely attributable to reductions in weed density and biomass, along with the well-documented agronomic benefits of rolled cereal rye residue, such as improved water infiltration, decreased soil moisture loss through evaporation, and enhanced soil quality (Scavo et al. Reference Scavo, Fontanazza, Restuccia, Pesce, Abbate and Mauromicale2020; Silva and Bagavathiannan Reference Silva and Bagavathiannan2022). Across all termination timings and herbicide programs, there was a consistent trend of reduced yield in the standing cereal rye residue treatments. Peanut yield decreased by 8% to 33% relative to rolled cereal rye and winter fallow control, for both early and late termination timings, when standing cereal rye residue was present. The reduced yield observed in the standing cereal rye treatments may be attributed to increased peanut plant height (data not shown) or etiolation, potentially induced by shading from the standing cereal rye residue. This response could have led to reduced flower retention and lower belowground resource acquisition (Barbour et al. Reference Barbour, Bridges, Scott and Nesmith1994). Similar findings have been reported previously, where shading-induced etiolation in peanut reduced light-use efficiency, pod formation, and yield (Adjhahossou et al. 2008; Stirling et al. Reference Stirling, Williams, Black and Ong1990).
Table 7. Effect of cereal rye termination management and herbicide program interaction on peanut yielda–e.
a Abbreviations: EPOST, early postemergence; MPOST, mid-postemergence; PRE, preemergence.
b Means within a column followed by a different letter are significantly different at α ≤ 0.05. Standard errors are presented in parentheses.
c PRE + EPOST + MPOST indicates a PRE application of fluridone followed by an EPOST application of paraquat + S-metolachlor + bentazon at 30 d after planting followed by an MPOST application of imazapic + dimethenamid-P + 2,4-DB at 60 d after planting.
d PRE + MPOST indicates a PRE application of flumioxazin followed by an MPOST application of acifluorfen + dimethenamid-P + 2,4-DB at 60 d after planting.
e EPOST + MPOST indicates an EPOST application of imazapic + dimethenamid-P + 2,4-DB at 30 d after planting followed by an MPOST application of premixed bentazon + acifluorfen + S-metolachlor + 2,4-DB at 60 d after planting.
Regardless of cereal rye residue management (rolled or standing), peanut yield did not differ between the early and late cereal rye termination timings when an intensive herbicide program (preemergence + early postemergence + mid-postemergence) was used. However, herbicide input was reduced (either a preemergence + mid-postemergence or an early postemergence + mid-postemergence application), late-terminated cereal rye residue resulted in 9% to 27% higher peanut yields than when cereal rye was terminated early (Table 7). Notably, when cereal rye was terminated late and rolled flat, yield under the reduced herbicide program (early postemergence + mid-postemergence; 4,373 kg ha−1) was comparable to that of the highest-yielding treatments that included intensive herbicide input with rolled cereal rye residue or winter fallow control (4,225 to 4,406 kg ha−1). These results suggest that late-terminated, rolled cereal rye can supplement weed management and reduce one’s reliance on preemergence herbicides in peanut production without compromising yield. Nonetheless, preemergence herbicides remain essential for consistent Amaranthus management, particularly given the limited and resistance-prone postemergence options available in peanut production. The observed yield improvements are likely due to the synergistic effects of greater cereal rye biomass at late termination and timely application of early postemergence and mid-postemergence herbicides, which provided weed control levels similar to those achieved with intensive herbicide programs. These findings are most relevant to peanut production in the southern United States, where herbicide options are limited and longer seasons allow greater rye biomass accumulation. In contrast, cropping systems such as corn and soybean have broader herbicide options and, in cooler northern regions, less cover crop biomass.
Regardless of termination management, treatments that included a reduced herbicide input (preemergence + mid-postemergence) produced 8% to 42% lower peanut yields compared with the highest-yielding treatments that included intensive herbicide input. This underscores the critical role of early postemergence herbicide applications in maximizing peanut yield, regardless of the presence of cereal rye cover crop. Since cereal rye residue did not persist throughout the season, treatments that lacked an early postemergence application had higher mid- and late-season weed densities and biomass, which likely contributed to the observed yield losses. Although a mid-postemergence herbicide application improved late-season weed control, it is probable that the crop suffered irrevocable yield losses due to weed competition during the critical weed-free period of 3 to 8 wk after crop emergence.
Practical implications
This study affirms the value of planting cereal rye cover crops for early season weed suppression in peanut production systems. The results suggest that rolled cereal rye with sufficient biomass accumulation can help the reduce on reliance herbicides without compromising peanut yield. However, the effectiveness of cereal rye residue for weed suppression is species-specific: while early cereal rye termination at 14 DPP suppressed Palmer amaranth, it did not adequately suppress sicklepod. Based on the rapid growth and extended emergence window of sicklepod, late termination of cereal rye is necessary to ensure adequate biomass for effective early season suppression in the absence of preemergence herbicides. However, cereal rye cover crop should not be considered a stand-alone replacement for preemergence herbicides but rather a complementary tool within an integrated weed management strategy.
Beyond weed suppression, high-biomass cereal rye residue also has implications for peanut establishment and harvest. Peanut yields were reduced when residue remained standing, likely due to interference with seedling emergence and early growth, whereas rolling the biomass at termination improved peanut establishment and yield outcomes. Importantly, when managed properly, rolled rye residue did not interfere with digging or inversion at harvest, indicating compatibility with conventional peanut harvesting practices. When cereal rye was terminated late and rolled flat, a reduced-input herbicide program (early postemergence + mid-postemergence) resulted in yields that were comparable to those achieved with intensive herbicide applications (preemergence + early postemergence + mid-postemergence) in the absence of cereal rye residue. This indicates that the potential exists to reduce herbicide inputs when cereal rye cover crops are properly managed. However, effective mid- and late-season weed control and consequently high yields could not be achieved without early postemergence applications, regardless of cereal rye presence. The rapid growth and season-long emergence of Palmer amaranth and sicklepod underscore the critical role of timely early postemergence herbicide applications. In conclusion, cereal rye cover crops can effectively complement or partially substitute preemergence herbicides depending on weed seedbank density, but they do not eliminate the need for early postemergence applications. Based on our results, we recommend terminating cereal rye cover crop 14 DPP and rolling the residue to optimize weed suppression and peanut yield. Timely early postemergence applications should remain a priority in any herbicide program, with or without a cereal rye cover crop.
Acknowledgment
We thank the field technical support team at West Florida Research and Education Center, in Jay, Florida, for their technical support.
Funding
This research is supported by the U.S. Department of Agriculture–National Institute of Food and Agriculture, through Hatch Project FLAWFC-005843, and by Florida peanut producers/check off fund G000430-2200-60820000-209-P0177604.
Competing Interests
The authors declare the have no competing interests.
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