Introduction
Conservation tillage systems offer producers numerous benefits that can maximize crop production and result in positive environmental impacts. Derpsch et al. (Reference Derpsch, Friedrich, Kassam and Li2010) reported that no-tillage and reduced-tillage systems can result in improvement in soil structure, increased organic matter content, and greater water retention. Additionally, implementation of minimum tillage production practices can also positively impact greenhouse gas emissions and promotion of carbon sequestration as well as overall agriculture sustainability (Lal Reference Lal2018; Srivastava Reference Srivastava2025). Such benefits have resulted in adoption of on-farm conservation practices. In 2024, a Conservation Effects Assessment Project (CEAP) survey of 6,245 producers across the United States conducted by the National Agricultural Statistics Service (NASS) and USDA Natural Resources Conservation Services (NRCS) indicated that almost 81% of respondents utilized conservation practices on their cropland (USDA 2024). Also, 83.3% reported utilizing no-till or minimum tillage to manage pests applied to almost 73% of the cropland surveyed. These findings continued a trend based on results from a CEAP II survey conducted from 2013 through 2016, which indicated that almost 87% of U.S. cultivated cropland acres utilized some form of conservation tillage for at least one crop in a crop rotation (USDA 2022).
Elimination or reduction of tillage operations in conservation systems require additional inputs of herbicides before planting to effectively manage winter weed species present to eliminate early-season competition. Numerous herbicide options are currently available that provide effective control of these weed populations in corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] (Anonymous 2026a, 2026b, 2026c, 2026d). Limitations to the effectiveness of preplant “burndown” herbicide programs in these crops include presence of resistant and/or hard to control weed species and often require a programs approach with varying strategies to maximize control (Salas et al. Reference Salas, Burgos, Tranel, Singh, Glasglow, Scott and Nichols2016; Varanasi et al. Reference Varanasi, Brabham, Norsworthy, Nie, Young, Houston, Barber and Scott2018; Westerveld et al. Reference Westerveld, Soltari, Hooker, Robinson and Sikkema2021).
Trifludimoxazin, a new protoporphyrinogen oxidase (PPO)-inhibiting herbicide developed by BASF that is awaiting registration by the U.S. Environmental Protection Agency (USEPA), has demonstrated preemergence and postemergence activity on a number of grass and broadleaf weeds including annual ryegrass [Lolium perenne (L.) ssp. multiflorum (Lam.) Husnot], giant foxtail [Setaria faberi Herrm.], junglerice (Echinochloa colona (L.)), johnsongrass [Sorghum halepense (L.) Pers.], green foxtail [Setaria viridis (L.) P. Beauv.], large crabgrass [Digitaria sanguinalis (L.) Scop.], horseweed [Erigeron canadensis L.; syn.: Conyza canadensis (L.) Cronquist], redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.), and kochia [Bassia scoparia (L.) A.J. Scott] (Rapado et al. Reference Rapado, Kolpin, Zeyer, Anders, Piccard, Porri and Asher2025). Additionally, the herbicide has been reported to be a potent PPO-inhibiting herbicide that inhibits the PPO2 enzyme that carries target-site mutations that could be utilized to mitigate widespread occurrence of PPO target-site resistance and resistance to other modes of action (Porri et al. Reference Porri, Betz, Seebruk, Knapp, Johen, Witschel, Aponte, Liebl, Tranel and Lerchl2023). Saflufenacil, also a PPO-inhibiting herbicide commercialized by BASF, is labeled for preplant application in crops including soybean, corn, cotton, and rice (Oryza sativa L.) and exhibits good activity on a number of common winter annual weeds (Anonymous 2024, 2026a, 2026b. 2026c. 2026d). Improved burndown weed control and longer soil residual activity have been reported with combinations of trifludimoxazin and saflufenacil (Findley Reference Findley2020; Grey et al. Reference Grey, Newsome and Findley2020; Rapado et al. Reference Rapado, Kolpin, Zeyer, Anders, Piccard, Porri and Asher2025). Registration is pending by USEPA for a premix herbicide containing both trifludimoxazin and saflufenacil for burndown application ahead of planting corn, soybean, grain sorghum [Sorghum bicolor (L.) Moench ], and wheat (Triticum aestivum L.).
Soybean was planted on more than 33 million ha in the United States in 2025 (USDA 2025). With early-season soybean growth often occurring simultaneously with preplant burndown of fields in later-planted soybean and grain sorghum, odds of negative impacts associated with off-target herbicide movement to the crop increase. Previous surveys of agronomic crop producers in multiple states identified drift or off-target movement as the largest herbicide application challenge (Butts et al. Reference Butts, Barber, Norsworthy and Davis2021; Virk and Prostko Reference Virk and Prostko2022). Previous research has also documented the characterization and negative impacts associated with herbicide drift to non-target species (Moore et al. Reference Moore, Priest, Brayden, Hanzas, Arpino, Richardson, Stryker, Banman, Rodney, Chapple, Hall, Isemer, Ortego, Rodea-Palomares and Tang2022; Perkins et al. Reference Perkins, Abi-Akar, Goodwin and Brain2022; Strandberg et al. Reference Strandberg, Sørensen, Bruus, Bossi, Dupont, Link and Damgaard2021). Therefore, it is critical to have a good understanding of the implications on crop development and subsequent yield should exposure to an off-target herbicide event occur.
Most commercially available PPO-inhibiting herbicides, including saflufenacil, are labeled for use in soybean (Anonymous 2026a, 2026b, 2026c, 2026d). Although well tolerated by soybean, postemergence application of labeled PPO-inhibiting herbicides can result in initial crop injury. Priess et al. (Reference Priess, Norsworthy, Roberts and Gbur2020) reported that acifluorfen and fomesafen resulted in 14% to 15% phytotoxic response at 14 d after treatment (DAT) to 2-leaf soybean. Additionally, these treatments resulted in a minimum 4-d delay in achieving 80% canopy formation. Thes early-season impacts did not result in significant yield decrease, however. Saflufenacil applied postemergence at rates ranging from 1.09 to 70 g ha−1 to simulate tank contamination injured V3 to V4 soybean 13% to 90% at 2 WAT and 4% to 85% at 5 WAT (Galon et al. Reference Galon, Tedesco, Tonin, Ribeiro dos Anjos, Giacomolli, Dassoler, Ortiz and Perin2025). Additionally, soybean yield was reduced at saflufenacil rates of 4.4 g ha−1 or greater. The PPO-inhibiting herbicide tiafenacil is labeled for use preplant burndown before soybean planting (Anonymous 2026a, 2026b, 2026c, 2026d). Also, previous published and unpublished research has indicated that tiafenacil can injure soybean foliage and provide very effective defoliation of soybean before harvest (Miller et al. Reference Miller, Stephenson, Barber, Doherty and Mize2021; DKM, personal observation).
To our knowledge, there exists no published information documenting susceptibility of early vegetative stage soybean to foliar-applied trifludimoxazin + saflufenacil at rates encountered in off-target/drift events. Therefore, the objective of this research was to document any negative impacts of foliar application of trifludimoxazin + saflufenacil to soybean growth and yield.
Materials and Methods
Field Trial Establishment
Field experiments were conducted in 2024 at the LSU AgCenter Northeast Research Station near St Joseph, LA (31.9184°N, 91.2335°W), the LSU AgCenter Doyle Chambers Central Research Station near Baton Rouge, LA (30.3756°N, 91.1712°W), the University of Arkansas System Division of Agriculture Lonoke Extension Center in Lonoke, AR (34.7843°N, 91.9001°W), the University of Tennessee AgResearch and Education Center in Milan, TN (35.9198°N, 88.7589°W), the University of Missouri Fisher Delta Research Center in Portageville, MO (36.411°N, 89.697°W), the Kansas State University Agricultural Research Center–Hays (38.857485°N, 99.3328492°W), and the North Carolina State University Upper Coastal Plain Research Station in Rocky Mount, NC (35.89295°N, 77.67996°W) to determine the impact of reduced rates of trifludimoxazin + saflufenacil (BASF, Research Triangle Park, NC) on soybean growth and yield. Experiments were conducted in a randomized complete block design with treatments replicated three to four times. Treatments were applied via compressed air or CO2-pressurized backpack sprayer at 140 L ha−1. Treatments included reduced rates of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× rate applied to 1- to 2-leaf soybean. The growth stage chosen is representative as most likely to coincide when burndown of later-planted grain sorghum or soybean ground occurs. The 1× rate basis for reduced rate calculation was 38.3 g ai ha−1. Previous unpublished research has indicated that this rate in combination with glyphosate provides effective control of most common winter annual weed species before planting (DKM, personal observation). Methylated seed oil (MSO) was added at 1% v/v to all treatments. A comparison 1% MSO-alone treatment was included but resulted in no impacts on parameters measured in comparison to the 0× rate and therefore was excluded from statistical analysis. Trifludimoxazin + saflufenacil at designated rates was applied to 1- to 2- leaf soybean variety ‘P48Z70BLX’ near St Joseph on May 20, variety ‘P48Z70BLX’ near Baton Rouge on May 26, variety ‘P48A14E’ in Lonoke on June 14, variety ‘AG47xF2’’ in Milan on June 6, variety ‘Progeny 4604’ in Portageville on July 8, variety ‘3821R2X/SR in Hays, and variety ‘AG53x52’ in Rocky Mount on June 28. Herbicide application timing was determined as the most likely growth stage to be present when burndown of delayed planted soybean and grain sorghum production fields occur in Midsouth production areas (authors’ personal observations). As-needed application of glyphosate (Roundup PowerMax® 3, Monsanto, St Louis, MO) at 1,120 g ha−1 plus glufosinate (Liberty® 280 SL, BASF) at 420 g ha−1 was applied to eliminate any weed competition or interference impacts on results. Parameter measurements to assess treatment impacts included visual phytotoxicity on a scale of 0% equals no injury and 100% equals plant death at 1, 2, and 4 WAT; plant height at 2 and 4 WAT; and yield.
Statistical Analysis
The four-parameter log-logistic model was fit to soybean injury (1, 2, and 4 WAT), soybean height injury (2 and 4 WAT), and yield data.
\begin{equation} Y = c + {\rm{ }}{{d - c} \over {1 + \exp\left[ {b\left( {\ln\left( x \right) - \ln\;\left( e \right)} \right)} \right]}} \end{equation}
where Y is injury (%), height (cm), and yield (kg ha−1); b is the slope at the inflection point; c is the lower limit; d is the upper limit; e is the dose of herbicide corresponding to the midpoint of plant injury response observed between the upper and lower limits; and x is the fraction of the labeled rate of the premixture of trifludimoxazin + saflufenacil tested (Tables 1, 2, and 3). Data were analyzed by location and model parameters compared (Ritz et al. 2015) with no statistical differences detected between parameters of locations (data not shown). Therefore, data were pooled across location for curve fitting. All curve fittings were accomplished using the nonlinear least-squares regression (nls) function in R v. 4.1.2 (R Core Team 2024). Before fitting the equation, we assessed model assumptions using different statistical tests. A lack-of-fit test was used to compare the chosen nonlinear regression model to a more general ANOVA model (Ritz and Streibig Reference Ritz and Streibig2008). Variance homogeneity was evaluated using Levene’s test. The Shapiro-Wilk test was used to assess whether residuals were normally distributed. The four-parameter log-logistic model was fit to all parameters measured averaged across locations.
Nonlinear regression parameters for soybean visual injury at 1, 2, and 4 wk after treatment (WAT). a
a Trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
The four-parameter log-logistic model was fit where Y is injury (%), b is the slope at the inflection point, c is the lower limit, d is the upper limit, e is the dose of herbicide corresponding to the midpoint of plant injury response observed between the upper and lower limits, and x is the fraction of the labeled rate of the premixture of trifludimoxazin + saflufenacil tested.
Nonlinear regression parameters for soybean height at 2 and 4 wk after treatment (WAT). a
a Trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC. The four-parameter log-logistic model was fit where Y is height (cm), b is the slope at the inflection point, c is the lower limit, d is the upper limit, e is the dose of herbicide corresponding to the midpoint of plant injury response observed between the upper and lower limits, and x is the fraction of the labeled rate of the premixture of trifludimoxazin + saflufenacil tested.
Nonlinear regression parameters for soybean yield. a
a Trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC. The four-parameter log-logistic model was fit where Y is yield (kg ha−1), b is the slope at the inflection point, c is the lower limit, d is the upper limit, e is the dose of herbicide corresponding to the midpoint of plant injury response observed between the upper and lower limits, and x is the fraction of the labeled rate of the premixture of trifludimoxazin + saflufenacil tested.
Results and Discussion
Soybean Phytotoxicity
Soybean phytotoxicity manifested primarily as necrotic leaf speckling and lower plant population as a result of plant death at higher rates. Each successive reduced rate of trifludimoxazin + saflufenacil applied resulted in 53%, 43%, 32%, 21%, 13%, and 8% soybean phytotoxicity at 1 WAT (Figure 1). Plant response was 31%, 23%, 17%, 12%, 8%, and 5% at these same rates at 2 WAT (Figure 2). By 4 WAT, visual phytotoxicity for the three highest rates applied averaged 14%, 11%, and 7%, while lower rates resulted in no greater than 4% (Figure 3). Previous research with saflufenacil applied postemergence at rates ranging from 1.09 to 70 g ha−1 to simulate tank contamination injured V3 to V4 soybean 13% to 90% at 2 WAT and 4% to 85% at 5 WAT (Galon et al. Reference Galon, Tedesco, Tonin, Ribeiro dos Anjos, Giacomolli, Dassoler, Ortiz and Perin2025). This range represents a 1/66× to 1× rate of the amount of saflufenacil in a 1× rate of trifludimoxazin + saflufenacil. In addition, Miller et al. (Reference Miller, Bond, Butts, Steckel, Stephenson and Kouame2024) reported that at 1 WAT, tiafenacil applied at 1/8×, 1/16×, 1/32×, and 1/64× rates to 1- to 2-leaf soybean exhibited 80%, 61%, 39%, and 21% visual injury, while at 4 WAT, these respective rates resulted in visual injury of 67%, 33%, 14%, and 4%.
Soybean visual injury at 1 wk after treatment (WAT) as impacted by reduced rate of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
Soybean visual injury at 2 wk after treatment (WAT) as impacted by reduced rate of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
Soybean visual injury at 4 wk after treatment (WAT) as impacted by reduced rate of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
Soybean Height
The three highest rates of trifludimoxazin + saflufenacil applied resulted in height reduction of 30% to 13% and 7% by the 1/64× rate at 2 WAT (Figure 4). The lowest rates applied reduced height no greater than 2%. At 4 WAT, height was reduced 18% to 7% by the three highest trifludimoxazin + saflufenacil rates and 4% by the 1/64× rate, while the lowest rates applied reduced height no greater than 2% (Figure 5). Tiafenacil applied at 1/8×, 1/16×, 1/32×, and 1/64× reduced soybean height 55% to 2% and 53% to 5% at 1 and 4 WAT, respectively (Miller et al. Reference Miller, Bond, Butts, Steckel, Stephenson and Kouame2024). These results and results from the current research indicate greater sensitivity of early-season soybean growth to off-target movement of tiafenacil compared with trifludimoxazin + saflufenacil at higher rates evaluated.
Soybean height at 2 wk after treatment (WAT) as impacted by reduced rate of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
Soybean height at 4 wk after treatment (WAT) as impacted by reduced rate of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
Soybean Yield
Soybean yield following exposure to trifludimoxazin + saflufenacil at the 1/8× rate was reduced 8% (Figure 6). Trifludimoxazin + saflufenacil applied at the 1/16× rate resulted in reduced yield of 5%, while lower rates reduced yield no greater than 2%. Previous research with saflufenacil applied postemergence to V3 to V4 soybean at rates greater than 4.4 g ha−1 to simulate tank contamination resulted in at least an 8% reduction in yield, while lower rates did not. This rate corresponds to a 1/16× rate of saflufenacil in the trifludimoxazin + saflufenacil compound. Conversely, the 1/8×, 1/16×, 1/32×, and 1/64× rates of tiafenacil reduced soybean yield 53%, 24%, 5%, and 1% (Miller et al. Reference Miller, Bond, Butts, Steckel, Stephenson and Kouame2024). These results and results from the current research indicate greater sensitivity of soybean to tiafenacil compared with other PPO-inhibiting herbicides, including trifludimoxazin + saflufenacil.
Soybean yield as impacted by reduced rate of trifludimoxazin + saflufenacil at 0×, 1/8×, 1/16×, 1/32×, 1/64×, 1/128×, and 1/256× of a 38.3 g ai ha−1 use rate applied to 1- to 2-leaf soybean for data collected in 2024 at St Joseph, LA; Baton Rouge, LA; Lonoke, AR; Milan, TN; Portageville, MO; Hays, KS; and Rocky Mount, NC.
In summary, substantial soybean visual phytotoxicity including plant death was observed early season in response to trifludimoxazin + saflufenacil rates ranging from 12.5% to 1.6% of a 1× use rate (38.3 g ai ha−1) that did lessen over time. This visual injury resulted in significant height reduction, especially at the four highest rates applied; however, yield was reduced no greater 2% at rates below 1/16x. In comparison to previous research conducted on PPO-inhibiting herbicides labeled for use in crop (Priess et al. Reference Priess, Norsworthy, Roberts and Gbur2020), soybean season-long response to off-target application of trifludimoxazin + saflufenacil would be greater but less so than to the PPO-inhibiting herbicide tiafenacil (Miller et al. Reference Miller, Bond, Butts, Steckel, Stephenson and Kouame2024). Still, application of trifludimoxazin + saflufenacil to soybean in early vegetative stages of growth should be avoided. Off-target movement of trifludimoxazin + saflufenacil to soybean in early vegetative growth will result in severe phytotoxicity and height reduction, especially with exposure at the three highest rates evaluated. Soybean should not be expected to completely recover, and significant negative impact on yield (5% or greater) will be observed at the two highest rates evaluated in this research.
Funding statement
The authors wish to thank the Louisiana Soybean and Feed-grain Research and Promotion Board for providing partial funding of this project.
Competing interests
The authors declare no conflicts of interest.
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