Study locations and conditions

Experiments were conducted from early Jul 2023 to late Sep 2024 at the West Florida Research and Education Center (WFREC) in Jay, FL, USA (lat. 30.77°N, long. 87.14°W), and the Plant Science Research and Education Unit (PSREU) in Citra, FL, USA (lat. 29.41°N, long. 82.17°W). These experiments were repeated in time/space for a total of 2 site–years. The turf was ‘CR-01’ and ‘Tifway’ (also colloquially referred to as ‘Tifway 419’) hybrid bermudagrass at WFREC, and ‘Floratam’ and ‘Seville’ St. Augustinegrass at WFREC and PSREU, respectively. In hybrid bermudagrass, standard cultural practices for golf course fairway/athletic field maintenance were used, including mowing 3 times·wk⁻¹ at 0.5 inches and fertility of 5.0 lb N·1000 ft⁻²·yr⁻¹. In St. Augustinegrass, standard cultural practices for a home lawn maintenance were used, including mowing weekly at 3.5 inches and fertility of 5.0 lb N·1000 ft⁻²·yr⁻¹. At both hybrid bermudagrass sites, established and mature (tillering) doveweed populations were present, allowing evaluations of both weed control and hybrid bermudagrass safety response. In contrast, St. Augustinegrass sites were weed-free and served only to assess St. Augustinegrass safety response.

Herbicide treatments

Herbicide treatments, rates, and application intervals were the same across all individual experiments (Tables 3-6). Individual plots were 5 ft × 5 ft. Herbicides tested included combinations of mesotrione (Tenacity; Syngenta Crop Protection, LLC, Greensboro, NC, USA), simazine (Princep Liquid; Syngenta Crop Protection, LLC, Greensboro, NC, USA), and a premix of trifloxysulfuron and metcamifen (Recognition; Syngenta Crop Protection, LLC, Greensboro, NC, USA). Metcamifen is a proprietary safener and an inert compound with no specified load on the product label; therefore, its exact rate was unknown and depended on the product rate. As a result, only the rate of trifloxysulfuron is provided. Nonionic surfactant (Induce; Helena Agri-Enterprises, LLC, Collierville, TN, USA) was included at 0.25% v/v with all herbicide treatments. All herbicide applications were made using a CO₂-powered backpack sprayer (R&D Sprayers, Bellspray, Inc., Opelousas, LA, USA) equipped with four TeeJet 8003VS flat-fan spray tips (TeeJet Technologies, Spraying Systems Co., Glendale Heights, IL, USA) calibrated to deliver 2 gal·1000 ft⁻² of spray solution to enhance canopy penetration and promote root absorption.

Assessments and data collection

All evaluations were conducted at study initiation, 1 week after the initial treatment (WAIT), 2 WAIT, and biweekly thereafter; evaluations concluded at 10 WAIT. To assess herbicide efficacy, plots were visually evaluated for doveweed pressure expressed as weed cover (0%–100%) and doveweed control expressed as the percentage of the ratio between the initial weed cover and weed cover at the time of the evaluation [0%–100% scale; 0% = no control; 80% = minimum acceptable control (i.e., acceptability threshold); 100% = complete control]. To assess hybrid bermudagrass and St. Augustinegrass safety responses, plots were visually evaluated for turfgrass injury [0%–100% scale; 0% = no damage; 20% = maximum acceptable injury (i.e., acceptability threshold); 100% = dead turfgrass]. The threshold values used in this study were selected as practical benchmarks widely adopted in turfgrass and weed science research efficacy: 80% of minimum acceptable weed control defined commercially acceptable herbicide (Askew et al. 2025; Brewer and Askew 2021; Gawron et al. 2025) and 20% turfgrass injury defined tolerable temporary phytotoxicity (Boeri et al. 2021; Patton et al. 2021; Peppers et al. 2024). To account for repeated observations over time and clearly illustrate the duration of effective control and/or severity of injury in a practical way, the durations (in days) when doveweed control was >80% (DOT_80%) and when turfgrass injury was >20% (DOT_20%) were calculated using the approach of Cox et al. (2017). Furthermore, the highest recorded turfgrass injury (turfgrass injury maxima) for each plot was determined as the maximum observed injury rating across all data collection timings (Brewer and Askew 2021). These measurements are becoming more widely used in scientific literature offering turf managers essential information for making informed herbicide decisions (Askew et al. 2013; Brewer and Askew 2021; Brewer et al. 2022a, 2022b; Cox et al. 2017; Gawron et al. 2025; Peppers and Askew 2023; Petelewicz et al. 2025).

Statistical design and analysis

All experiments used a complete randomized block design with four replications. Doveweed control and turfgrass injury data were analyzed using linear mixed models with repeated measurements, with site–year, treatment, data collection timing (term), and their interactions included as fixed effects. Replication was included in the model as a random intercept, and term was modeled with a first-order autoregressive residual correlation grouped within each plot. Transformed variables (DOT_80% doveweed control; DOT_20% turfgrass injury; and turfgrass injury maxima) were analyzed using linear models with site–year, treatment, and their interactions as fixed effects. Assumptions for the analysis of variance were checked for each variable, and no transformation was applied. All data were presented based on the significance levels of interaction. Analyses of variance were conducted in R using the tidyverse, emmeans, multicomp, and nlme packages (Hothorn et al. 2008; Lenth 2023; Pinheiro 2023; R Core Team 2020; Wickham et al. 2019). When appropriate, means were compared using Fisher’s protected least significant difference (LSD) test, with significance considered at P = 0.05 (Bates et al. 2015; Lenth 2023; R Core Team 2020; Wickham et al. 2019).

Doveweed control

The site–year × treatment × term interaction was significant for doveweed control (Table 2); therefore, data were analyzed separately by site–year and within each site–year by timing (Table 3). The site–year × treatment interaction was significant for DOT_80% doveweed control (Table 2); therefore, data were separated by site–year (Table 4).

Table 2. Results of the analysis of variance (ANOVA) of the effects of treatment, data collection timing (term), site–year, and their interactions on doveweed control, bermudagrass injury, and St. Augustinegrass injury as well as of treatment, site–year, and their interactions on days over threshold of 80% (DOT_80%) doveweed control, days over threshold of 20% (DOT_20%) turfgrass injury, and turfgrass injury maxima in ‘CR-01’, ‘Tifway’ hybrid bermudagrass golf course fairway/athletic field and ‘Floratam’, ‘Seville’ St. Augustinegrass home lawn at the West Florida Research and Education Center (WFREC) in Jay, FL, USA, and the Plant Science Research and Education Unit (PSREU) in Citra, FL, USA, 2023–24. Main effects and interactions that were significant for at least one measured parameter are presented.

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Table 3. Herbicide effects on doveweed control in ‘CR-01’ and ‘Tifway’ hybrid bermudagrass golf course fairway/athletic field at West Florida Research and Education Center, Jay, FL, USA 2023–24.

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Table 4. Herbicide effects on days over threshold of 80% (DOT_80%) doveweed control, turfgrass injury maxima, and days over threshold of 20% (DOT_20%) turfgrass injury in ‘CR-01’ and ‘Tifway’ hybrid bermudagrass golf course fairway/athletic field at West Florida Research and Education Center (WFREC), Jay, FL, USA, and ‘Floratam’ and ‘Seville’ St. Augustinegrass home lawn at WFREC and Plant Science Research and Education Unit (PSREU), Citra, FL, USA, 2023–24.

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Considering standalone applications first, only mesotrione in 2024 controlled doveweed satisfactorily (>80%) beginning at 6 WAIT (Table 3), resulting in DOT_80% doveweed control ranging from 25 to 32 (Table 4), with no significant difference between rates (Tables 3 and 4). No other standalone treatment exceeded doveweed control of 50% in either year (Table 3), resulting in negligible DOT_80% doveweed control throughout the study (Table 4). In 2023, both tank mixes applied at higher rates (with or without trifloxysulfuron and metcamifen) achieved acceptable control starting at 2 WAIT. While both lower-rate tank mixes lagged behind initially, only the mix containing trifloxysulfuron and metcamifen provided significantly lower control than the best-performing treatment at 2 and 4 WAIT. However, both lower-rate tank mixes achieved satisfactory control by 6 WAIT (Table 3). Ultimately, mesotrione and simazine tank mixes applied without trifloxysulfuron and metcamifen in 2023 achieved comparable DOT_80% doveweed control, ranging from approximately 7.5 to 8.5 weeks out of the 10-week observation period (Table 4). While the addition of trifloxysulfuron and metcamifen numerically reduced DOT_80% doveweed control across equivalent-rate tank mixes, the difference was only significant in the lower-rate mix, where control persistence was nearly halved (Table 4). In 2024, all tank mixes achieved satisfactory control beginning at 2 WAIT and exceeded 90% in all cases (Table 3); no significant differences in persistence were observed among tank mixes, with all achieving DOT_80% doveweed control of 8 to 8.5 weeks throughout the 10-week evaluation, which was nearly twice the persistence of mesotrione alone (Table 4). Additionally, in 2024, the inclusion of trifloxysulfuron and metcamifen had no impact on tank mix performance (Tables 3 and 4).

Mesotrione has demonstrated efficacy against various weeds, including both grassy (Beam et al. 2006; Brewer et al. 2017; Elmore et al. 2012, 2013a, 2022; Goddard et al. 2010; Johnson and Young 2002; Jones and Christians 2007; Mitchell et al. 2001; Petelewicz et al. 2025; Skelton et al. 2012) and broadleaf weeds (Brewer et al. 2017; Johnson and Young 2002; Mitchell et al. 2001; Sutton et al. 2002). However, when used alone, weed control with mesotrione has often been deemed inconsistent or insufficient (Brewer et al. 2017; Elmore et al. 2012, 2013a, 2022; Petelewicz et al. 2025; Reicher et al. 2011; Sousek and Reicher 2019). To our knowledge, this study is the first peer-reviewed investigation to explore its use against doveweed. Only Yu and McCullough (2016a) tested simazine against doveweed and found that when applied alone in a controlled environment, it produced 69% injury with foliar applications and ≥97% with soil only or foliar plus soil treatments. In this study, under field conditions, neither standalone treatment provided consistent satisfactory control (Tables 3 and 4, Fig. 1). This may have been expected for trifloxysulfuron and metcamifen because Sharpe and Boyd (2020) previously showed low (approximately 0%) to erratic (53%–98% depending on the run) doveweed control with trifloxysulfuron-sodium applied alone in a greenhouse study. Because herbicide placement plays a role in both doveweed control (Yu and McCullough 2016a) and mesotrione/simazine efficacy (Goddard et al. 2010; Yu and McCullough 2016a), their poor performance when used alone (Tables 3 and 4) may be partly attributable to limited root accessibility despite using higher carrier volume to enhance canopy penetration and facilitate soil absorption. Another potential justification is the excessive maturity level of the target weed at the time of application (Yu and McCullough 2016a, 2016b). Although earlier application to smaller weeds or strategies such as irrigation to enhance soil activity may potentially improve efficacy, further research is needed. Nevertheless, the results from this study (Tables 3 and 4), particularly those of DOT_80% doveweed control (Table 4), suggest that mesotrione, simazine, and trifloxysulfuron and metcamifen alone are not viable options for controlling established doveweed infestations.

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However, when mesotrione and simazine were combined in a tank mix (regardless of their rate), doveweed control was substantially enhanced in both response time and persistence, with documented improved DOT_80% doveweed control (Tables 3 and 4). This combination effectively mitigated the limitations of standalone applications despite targeting well-developed plants and without requiring modifications to the application strategy, thus making tank mixes the best-performing treatments in this research (Fig. 1). A similar response from combining these active ingredients (a.i.) was previously observed by Petelewicz et al. (2025), who reported that the tank mix of the two molecules enhanced goosegrass [Eleusine indica (L.) Gaertn.] control, thus extending DOT_80% goosegrass control persistence by two- to three-times compared with the best-performing components alone. Elmore et al. (2013a, 2022) reported improved control of annual bluegrass (Poa annua L.) with tank mixes of mesotrione and amicarbazone, another PS II inhibitor, compared with standalone applications of both. The additive relationship between mesotrione and other PS II inhibitors in cropping systems other than those with turfgrass has been well-documented (Abendroth et al. 2006). Because no difference in overall efficacy was observed between tank mix rates (Tables 3 and 4), turf managers should initially consider the lower rate and make adjustments as needed if control proves inadequate. Trifloxysulfuron and metcamifen inconsistently affected tank mix performance, reduced efficacy of the lower rate tank mix in 2023 (Tables 3 and 4), suggesting that higher mesotrione/simazine rates may be necessary when trifloxysulfuron and metcamifen are included.

Hybrid bermudagrass safety

The site–year × treatment × term interaction was significant for hybrid bermudagrass injury (Table 2); therefore, data were analyzed separately by site–year and within each site–year by timing (Table 5). The site–year × treatment interaction was not significant for DOT_20% hybrid bermudagrass injury, but it was significant for hybrid bermudagrass injury maxima (Table 2). Therefore, DOT_20% hybrid bermudagrass injury data were pooled across site–years (Table 4), whereas hybrid bermudagrass injury maxima were analyzed separately by site–year (Table 4).

Table 5. Herbicide effects on turfgrass injury in ‘CR-01’ and ‘Tifway’ hybrid bermudagrass golf course fairway/athletic field at West Florida Research and Education Center, Jay, FL, USA, 2023–24.

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Considering nonherbicidal injury to hybrid bermudagrass, no observable damage to nontreated plots from either biotic or abiotic factors occurred (Table 5, Fig. 2), resulting in no DOT_20% turfgrass injury throughout the study (Table 4). Simazine and trifloxysulfuron and metcamifen, when applied alone, caused minimal to no observable injury and did not differ from the nontreated control throughout the study, except for the higher simazine rate, which caused approximately 17% injury at 6 WAIT (Table 5, Fig. 2). Despite this, neither treatment differed from the control in turfgrass injury maxima or DOT_20% turfgrass injury (Table 4). In both years, all other treatments caused unacceptable (>20%) hybrid bermudagrass injury that followed a consistent pattern: peak injury occurred within the first 2 weeks after each application, followed by complete to near-complete recovery to levels not different from those of the control within 4 weeks (Table 5). The primary difference between years was that peak injury from tank mixes containing trifloxysulfuron and metcamifen for the initial application was delayed from 1 WAIT in 2023 to 2 WAIT in 2024; however, complete recovery still occurred by 4 WAIT (Table 5). Among those treatments that caused injury, the main differences were those in symptomology, which directly translated to varying phytotoxicity severity (Table 5), that were best reflected by the turfgrass injury maxima, and those in the total duration of unacceptable injury, which were measured by DOT_20% turfgrass (Table 4). Both mesotrione rates alone caused white discoloration (foliar bleaching) to hybrid bermudagrass canopy (Fig. 2), with turfgrass injury maxima of approximately 30% to 60% in 2023, where the higher rate caused more severe injury, and 35% to 40% in 2024, with no differences between rates (Table 4). However, only the higher rate produced greater DOT_20% turfgrass injury than the nontreated control, which persisted for approximately 3.5 weeks (Table 4). All tank mixes produced bleaching symptoms, which often progressed to straw-colored necrotic turf (Fig. 2), following the previously described timeline (Table 5), with turfgrass injury maxima typically ranging from 50% to 80% in both years (Table 4). In 2023, lower-rate tank mixes had lower injury maxima than higher-rate mixes of the same composition and were comparable to the higher mesotrione-alone rate, whereas adding trifloxysulfuron and metcamifen to the tank mix had no effect on the injury severity (Table 4). In 2024, only the lower-rate mix containing trifloxysulfuron and metcamifen had lower turfgrass injury maxima than all other tank mixes and was comparable to mesotrione alone (Table 4, Fig. 2). Overall, unacceptable conditions, as indicated by DOT_20% turfgrass injury, persisted for 4 to 6 weeks, with lower rates reducing persistence by nearly one-quarter and trifloxysulfuron and metcamifen showing no effect (Table 4).

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The response of hybrid bermudagrass to herbicides in this study (Tables 4 and 5) largely aligns with previous literature. Foliar bleaching from mesotrione alone (Fig. 2) persisted between 1 and 4 weeks after each application, with both its duration and severity being primarily rate-dependent (Tables 4 and 5). Brewer et al. (2022a) similarly reported turfgrass injury maxima to hybrid bermudagrass that ranged from 68% to 84%, with white discoloration persisting over 3 weeks. Kerr et al. (2019) observed mesotrione-induced discoloration that peaked at 29% at 1 WAIT before recovering to acceptable levels from 2 WAIT onward. Petelewicz et al. (2025) documented mesotrione-related injury, with unacceptable symptoms lasting from 2 to 3 weeks to more than 6 weeks, depending on the year; however, their study focused on a more susceptible putting green setting. Contrary to these findings, Lindsey et al. (2019) reported no bermudagrass discoloration or clipping yield reduction following mesotrione application. Regarding simazine, minimal to no injury observed in this study (Tables 4 and 5, Fig. 2) was consistent with that reported by Kerr et al. (2019), Singh et al. (2015), and Lawson et al. (2002). Petelewicz et al. (2025) reported simazine injury; however, again, it was observed in a putting green scenario where turf tolerance was lower compared with the fairway-height setting of this study. Additionally, Petelewicz et al. (2025) observed substantially greater injury from mesotrione/simazine tank mixes compared with standalone applications, which is a trend that was mirrored in this study (Tables 4 and 5, Fig. 2) and in the study by Kerr et al. (2019), who documented peak injury increasing from 29% with mesotrione alone and 13% with simazine alone to 42% when combined. These findings suggest that turfgrass managers should anticipate significant, but transient, phytotoxicity when using mesotrione/simazine tank mixes for effective doveweed control. Such combinations comprise a final-line approach for severe and persistent infestations. Strategies like immediate postapplication irrigation could help minimize damage while maintaining or enhancing control; therefore, they should be further explored (Kerr et al. 2019; Petelewicz et al. 2025).

St. Augustinegrass safety

The site–year × treatment × term interaction was significant for St. Augustinegrass injury (Table 2); therefore, data were analyzed separately by site–year and within each site–year by timing (Table 6). The site–year × treatment interaction was significant for both DOT_20% St. Augustinegrass injury and turfgrass injury maxima (Table 2); therefore, both were analyzed separately by site–year (Table 4).

Table 6. Herbicide effects on turfgrass injury in ‘Floratam’ and ‘Seville’ St. Augustinegrass home lawn at West Florida Research and Education Center (WFREC), Jay, FL, USA, and Plant Science Research and Education Unit (PSREU), Citra, FL, USA, 2024.

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At WFREC, St. Augustinegrass exhibited minimal to no observable injury in both nontreated and herbicide-treated plots, except for slight foliage yellowing from the higher rate of mesotrione alone and tank mixes lacking trifloxysulfuron and metcamifen (Table 6, Fig. 3). Discoloration or injury in all cases followed a consistent pattern similar to hybrid bermudagrass: peak injury occurred within the first 2 weeks after each application, followed by complete recovery within 4 weeks. The only exception was the higher mesotrione rate, which at 4 WAIT remained greater than the control but was still below 5% and, thus, negligible (Table 6). The higher rate of mesotrione alone and tank mixes lacking trifloxysulfuron and metcamifen were the only treatments in which turfgrass injury maxima was significantly higher than that in nontreated plots, with the tank mix containing a higher mesotrione rate and producing greater injury compared with the other two (Table 4). Ultimately, only the higher-rate mesotrione/simazine tank mix resulted in unacceptable injury, with nearly 10 DOT_20% turfgrass injury recorded (Table 4). Including trifloxysulfuron and metcamifen in the tank mix reduced injury overall to levels nondifferent from those of the control plots (Table 6, Fig. 3) and resulted in lower turfgrass injury maxima and DOT_20% turfgrass injury with the higher-rate tank mix to levels comparable to those of the nontreated plots (Table 4).

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At PSREU, unacceptable turf damage was observed throughout the study, including in the control plots (Tables 4 and 6, Fig. 4). Severity increased over time, became significant from 4 WAIT onward, peaked across all treatments at 8 WAIT (Table 6, Fig. 4), and dissipated to acceptable levels by 10 WAIT (Table 6). Initially, the damage in nontreated plots was unnoticed because of the unbiased data collection approach and differential injury across treatments. Although a review of records revealed that pest activity may have occurred, retrospective identification was not possible. This resulted in a turfgrass injury maxima of nearly 30% in nontreated plots (Tables 4 and 6), leading to an unacceptable level of injury persisting for nearly 1 week, as indicated by DOT_20% turfgrass injury (Table 4). Mesotrione and simazine, whether applied alone or in tank mixes without trifloxysulfuron and metcamifen, produced inconsistent effects across all measured metrics, with no clear pattern and generally no significant differences from the nontreated plots (Tables 4 and 6). Exceptions with St. Augustinegrass injury exceeding that of the nontreated included both mesotrione alone rates at 4 WAIT, the higher simazine alone rate at 8 WAIT, the lower-rate tank mix at 8 WAIT, and the higher-rate tank mix at both 4 and 8 WAIT (Table 6). Among these, the higher-rate simazine alone treatment and both tank mixes without trifloxysulfuron and metcamifen nearly doubled turfgrass injury maxima compared with that of the nontreated, while the higher-rate tank mix also caused a four-fold increase in DOT_20% turfgrass injury relative to the control (Table 4). Trifloxysulfuron and metcamifen, whether applied alone or in tank mixes with mesotrione/simazine, produced the greatest phytotoxicity at 6 and 8 WAIT (Table 6, Fig. 4), resulting in turfgrass injury maxima that exceeded nontreated values by four-fold and three-fold, respectively (Table 4). Treatments containing trifloxysulfuron and metcamifen also extended DOT_20% turfgrass injury nearly six-fold compared with the nontreated (Table 4). No differences were observed among treatments containing trifloxysulfuron and metcamifen across any measured metrics (Tables 4 and 6), except at 10 WAIT, when injury from the lower-rate tank mix exceeded that of the higher-rate tank mix (Table 6). However, as with other treatments, the injury at this stage was already within an acceptable range (Table 6).

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The St. Augustinegrass response to the tested herbicides varied between the two locations (Tables 4 and 6, Figs. 3 and 4), offering important insights. At WFREC, the turf response appeared directly herbicide-dependent and followed an intuitive trajectory under optimal conditions. While minor injury occurred, it quickly recovered, and no treatment, except for the higher-rate tank mix, caused lasting unacceptable damage at any time. However, the inclusion of trifloxysulfuron and metcamifen successfully mitigated this injury as intended (Tables 4 and 6, Fig. 3). Trifloxysulfuron and metcamifen are specifically formulated for St. Augustinegrass safety and to alleviate injury when combined with certain herbicides in tank mixes. Its safening effect has been documented (Begitschke et al. 2022; Gawron et al. 2025; McFadden et al. 2023; Petelewicz, 2022; Rogers et al. 2023; Stoudemayer and McCarty, 2023; Wilber et al. 2022, 2023), and its performance in ‘Floratam’ at WFREC further supports these findings (Tables 4 and 6, Fig. 3). Notably, no peer-reviewed studies have examined the use of mesotrione or simazine, either alone or in tank mixes, in established St. Augustinegrass, thus making this the first report of such application. Mesotrione is labeled as only marginally safe for St. Augustinegrass; its use is prohibited in residential turf but permitted on sod farms only at a maximum rate of 175 g a.i.·ha⁻¹ (Syngenta 2022). This rate, which is the lower of the two tested in this study, was the only rate that did not differ from the nontreated in terms of turfgrass injury maxima at WFREC (Table 4). Simazine is labeled as safe for St. Augustinegrass when applied according to the directions (Syngenta 2021).

Unlike WFREC, the turf response at PSREU (Tables 4 and 6, Fig. 4) deviated from projections, likely influenced by external factors, and differed markedly from most existing literature (Begitschke et al. 2022; McFadden et al. 2023; Petelewicz 2022; Rogers et al. 2023; Stoudemayer and McCarty 2023; Wilber et al. 2022, 2023). Minimal to no unacceptable injury within the first 4 weeks (Table 6) suggested that the elevated damage observed in herbicide-treated plots, especially those containing trifloxysulfuron and metcamifen, was not a direct herbicidal effect, but rather a consequence of increased turf susceptibility to biotic and/or abiotic stressors following the second application. This ultimately led to a severe pest outbreak, although the specific disease could not be confirmed retroactively (Harmon P, personal communication). These findings, although attributed to different mechanisms (pest activity vs. potential growth regulation, seasonal timing, and/or cultivar sensitivity), align with the observations of Gawron et al. (2025), who also observed injury from trifloxysulfuron and metcamifen-based applications in ‘Seville’ St. Augustinegrass. Further research is needed to elucidate the factors behind this unforeseen response. Nevertheless, the results from WFREC suggest that mesotrione/simazine/trifloxysulfuron and metcamifen-based tank mixes may hold promise for late-season doveweed control in St. Augustinegrass and for label expansion to include residential uses.

Practical implications

Doveweed presents a significant challenge for turfgrass managers across the southeastern United States and Florida, especially once it becomes established, because most POST herbicides show reduced efficacy. Our results indicate that tank mixes of mesotrione and simazine deliver fast and effective control of mature doveweed under such circumstances. However, given the potential for temporary (up to 4 weeks) but severe injury to hybrid bermudagrass, these tank mixes may be better-suited as remedial approaches when infestations become unmanageable with other solutions. In such cases, these tank mixtures can help reduce weed pressure to levels that can be maintained with less injurious herbicide programs. Future research will explore such scenarios as well as safening strategies to minimize hybrid bermudagrass injury. In ‘Floratam’ St. Augustinegrass, injury was limited to slight yellowing, which was further reduced to levels comparable to those of untreated plots with the addition of trifloxysulfuron and metcamifen. Importantly, trifloxysulfuron and metcamifen did not compromise doveweed control, suggesting that these treatments may be suitable for lawn care. However, ‘Seville’ St. Augustinegrass grown at a north-central site exhibited severe damage throughout the study, particularly with treatments containing trifloxysulfuron and metcamifen. While this response was likely driven by nonherbicidal environmental stress, it underscores the need for additional cultivar-specific safety evaluations and highlights the practical value of conducting small-scale trials with trifloxysulfuron and metcamifen-based treatments, where injury is acceptable, before full broadcast applications are made. Finally, while this study focused on efficacy under worst-case conditions, real-world applications must account for label restrictions, especially those that limit simazine use during the summer. The simazine label section for turfgrass on fairways, lawns, and similar areas specifies that follow-up treatments for summer annual weeds must not be made after Jun 1, and that fall or winter treatments may begin after Sep 1 (Syngenta 2021), likely minimizing turf injury during periods of high temperature and drought stress. However, the results from this study do not suggest that turfgrass phytotoxicity from simazine alone during the summer months is a concern. From this perspective, future amendments to the label for warm-season turfgrass could be pursued if additional evidence supports its safety under those conditions.

Beyond efficacy against doveweed and turfgrass safety considerations, practical adoption of these treatments will depend on their economic feasibility. Based on currently available retail pricing (DoMyOwn, n.d.a, n.d.b; SiteOne, n.d.a, n.d.b), using original formulations as the reference, the estimated cost of mesotrione applied at 5.0 to 8.0 oz·acre⁻¹ ranges from approximately $34 to $93 acre⁻¹ and $55 to $149 acre⁻¹, respectively, while the cost of simazine applied at 15.0 to 25.0 oz·acre⁻¹ ranges from approximately $6 to $8 acre⁻¹ and $10 to $13 acre⁻¹, respectively. When combined in tank mixes, total treatment costs are estimated at approximately $40 to $101 acre⁻¹ for the 5.0 plus 15.0 oz·acre⁻¹ mixture and $65 to $161 acre⁻¹ for the 8.0 plus 25.0 oz·acre⁻¹ mixture, reflecting that mesotrione remains the primary driver of total cost across all combinations. The addition of trifloxysulfuron and metcamifen at 1.29 oz·acre⁻¹ would raise the cost of each tank mix by an additional approximately $145 acre⁻¹. Thus, from an economic standpoint, tank mixes of mesotrione and simazine increase the cost per application compared with standalone programs; however, given the minimal to no efficacy of either product applied alone and the drastically improved control achieved with tank mixes under worst-case scenarios, namely, late-season applications targeting mature doveweed populations, the added cost is justified.

Finally, while outside of the scope of this research, the environmental implications of the proposed treatments should also be considered. Generally speaking, both herbicides are considered low-toxicity herbicides to mammals or fish with low bioconcentration potential (Pfeuffer 2014; Sun et al. 2013); however, some persistence and potential off-site contamination implications exist. Mesotrione degrades relatively quickly under aerobic conditions, with a reported soil half-life ranging from 4 to 32 d under laboratory conditions and approximately 3 to 5 d or even 15 d in-field, depending on soil type and environmental conditions (Dyson et al. 2002; Gillespie et al. 2011; Sun et al. 2012). Although highly soluble, because of limited persistence and moderate adsorption, it exhibits low to moderate leaching potential (higher in sandy or high-pH soils), resulting in a relatively low risk of groundwater contamination when used according to label directions. However, its photolysis half-life in water is approximately 84 d, indicating that runoff to shallow ponds may pose an environmental concern (Food and Agriculture Corporation 2014; MDACF 2022; Sun et al. 2012; Williams 2008). In contrast, simazine is substantially more persistent, with a soil half-life of 46 to 174 d and moderate to high mobility in sandy soils with low organic matter, which are common in Florida (Pfeuffer 2014; World Health Organization 2003). While its persistence may extend residual soil activity and enhance PRE weed suppression, such specific effects on doveweed have not been documented. Despite low water solubility, simazine is classified as a leacher and has moderate potential for surface runoff, thus posing a greater long-term risk of groundwater contamination, particularly in Florida’s sandy soils (Choquette 2014; Pfeuffer 2014; World Health Organization 2003). Therefore, compliance with stewardship practices to minimize such environmental risk is required. However, because this information is primarily derived from, and therefore most applicable to, agronomic contexts, future studies should evaluate the environmental impacts regarding stormwater runoff and the leaching of pesticides and nutrients resulting from late-season herbicide applications on turfgrass systems. Nevertheless, considering these environmental implications and previously discussed injury potential of the mesotrione plus simazine combination for certain warm-season turfgrasses such as bermudagrass, it is important to reemphasize that this tank mix should serve as a last-resort cleanup treatment for severe doveweed infestations that helps reduce them to levels manageable with other herbicide options rather than a primary method for doveweed control.

In the near future, a mesotrione plus simazine-based strategy could also be integrated with modern ground-based targeted herbicide application systems equipped with artificial intelligence to detect weeds and activate individual nozzles with narrow spray bands along a broadcast-type boom. These systems enable herbicide delivery only where weeds occur, potentially reducing the treated area and corresponding environmental load by up to 80% (Joseph et al. 2025; McCurdy et al. 2025; Petelewicz et al. 2024). Integrating this technology with effective but injury-prone or environmentally sensitive herbicide strategies, such as those involving simazine, would help maintain efficacy while reducing turf injury, off-target risk, and environmental impact.