Introduction
Corn is the highest-value agronomic crop in Ontario. Weed interference can cause substantial yield losses of 50% if no weed management tactics are implemented (Soltani et al. Reference Soltani, Dille, Burke, Everman, VanGessel, Davis and Sikkema2016). The most common method of weed management is the application of herbicides, with 96% of planted corn acres receiving at least one herbicide application (USDA-NASS 2022).
Encapsulated saflufenacil + pyroxasulfone is a new herbicide premix for weed control in corn. Saflufenacil is a Group 14 protoporphyrinogen oxidase inhibitor and pyroxasulfone is a Group 15 very-long-chain fatty acid elongase inhibitor (Shaner Reference Shaner2014). The encapsulated saflufenacil + pyroxasulfone formulation will expand the herbicide application window and increase weed control options for Ontario corn producers. This new herbicide premix provides residual control of small-seeded annual grass and broadleaf weeds. Pyroxasulfone applied at 200 to 300 g ai ha−1 provides approximately 4 to 6 wk of residual control of select annual grass and broadleaf weeds (Knezevic et al. Reference Knezevic, Datta, Scott and Charvat2009). Saflufenacil at 75 g ha−1 provides residual control of common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and common ragweed (Ambrosia artemisiifolia L.) (Anonymous 2021, 2022; OMAFRA 2021).
Pyroxasulfone and saflufenacil provide primarily annual grass and broadleaf weed control, respectively; therefore, the combination has the potential to control a broader spectrum of weeds (Fillols et al. Reference Fillols, Davis, Lewis and Ward2020). Pyroxasulfone controls many small-seeded grass and broadleaf weeds including barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], foxtail species (Setaria sp.), large crabgrass [Digitaria sanguinalis (L.) Scop.], redroot pigweed, velvetleaf (Abutilon theophrasti Medik.), and waterhemp [Amaranthus tuberculatus (Moq.) J.D. Sauer] (Nurse et al. Reference Nurse, Sikkema and Robinson2011; OMAFRA 2021; Yamaji et al. Reference Yamaji, Honda, Kobayashi, Hanai and Inoue2014). The suspension concentrate formulation of saflufenacil controls many broadleaf weeds such as common lambsquarters, redroot pigweed, Canada fleabane [Conyza canadensis (L.) Cronq.], common ragweed, velvetleaf, wild buckwheat (Polygonum convolvulus L.), wild mustard (Sinapis arvensis L.), and stinkweed (Thlaspi arvense L.) (Boydston et al. Reference Boydston, Felix and Al-Khatib2012; Geier et al. Reference Geier, Stahlman and Charvat2009; OMAFRA 2021). Pyroxasulfone is used to control many small-seeded grasses and some broadleaf weeds, and saflufenacil is used to control many broadleaf weeds, thus this combination has the potential to control a broader spectrum of weeds than either active ingredient alone.
With respect to weed control, the interaction between active ingredients can be antagonistic, additive, or synergistic. Weed control interactions with two herbicides are determined by comparing observed and expected control with each active ingredient applied alone with the control of the combination (Akobundu et al. Reference Akobundu, Sweet and Duke1975; Green Reference Green1989). An antagonistic response is when the observed control is less than expected, an additive response is when the observed control is equal to expected, and a synergistic response is when the observed control is greater than expected. Herbicide interactions are specific to a weed species (Green Reference Green1989; Tidemann et al. Reference Tidemann, Hall, Johnson, Beckie, Sapsford, Willenborg and Raatz2014; Zhang et al. Reference Zhang, Hamill and Weaver1995). In previous research, the co-application of other herbicides in groups 14 and 15 has resulted in improved control of common lambsquarters, common ragweed, and green foxtail [Setaria viridis (L.) P. Beauv.] (Belfry et al. Reference Belfry, McNaughton and Sikkema2015). Research conducted by Tidemann et al. (Reference Tidemann, Hall, Johnson, Beckie, Sapsford, Willenborg and Raatz2014) established that the interaction between pyroxasulfone (Group 15) and sulfentrazone (Group 14) was additive; however, no previous research has been reported on the interaction between pyroxasulfone and saflufenacil.
Encapsulated saflufenacil + pyroxasulfone is a new herbicide premix, but limited data exist on it its ability to control problematic weeds in southwestern Ontario. The goal of this study was to ascertain the interaction between pyroxasulfone and encapsulated saflufenacil on visible weed control, density, and biomass of common weed species in southwestern Ontario as well as corn injury and yield.
Materials and Methods
A total of six field trials were conducted over a 2-yr period (2022 and 2023) in southwestern Ontario, Canada. Each year, two trials were established at the University of Guelph Ridgetown Campus, and one at the BASF research farm near Belmont. Trials consisted of 12 treatments set up as a randomized complete block design with four replicated blocks with 2- × 8-m plots. The trials were established using conventional tillage consisting of chisel ploughing in the fall and seedbed preparation in the spring using an S-tine cultivator with rolling basket harrows. Fertilizer was applied based on soil test results and Ontario Ministry of Agriculture, Food and Rural Affairs recommendations. Corn was planted at approximately 80,000 seeds ha−1, approximately 5 cm deep, in rows spaced 75 cm apart. Table 1 contains additional soil and crop information. Herbicide treatments consisted of three rates of pyroxasulfone (90, 120, and 150 g ai ha−1), saflufenacil (56, 75, and 95 g ai ha−1), encapsulated saflufenacil + pyroxasulfone (146, 195, and 245 g ai ha−1), and an industry-standard, S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1). Treatments were applied preemergence using a CO2-pressurized backpack sprayer calibrated to deliver 200 L ha−1.
Table 1. Year; location; soil characteristics; corn hybrid; planting, emergence, harvest, and herbicide application dates. a,b
a Abbreviations: CEC, cation exchange capacity; OM, organic matter.
b Six trials were conducted in Ontario, Canada, in 2022 and 2023.
Visible corn injury and weed control ratings were completed on a 0% to 100% scale, with 0% being no visible symptoms and 100% being complete plant death. Visible crop injury assessments were completed at 1, 2, and 4 wk after corn emergence (WAE) and visible weed control at 4 and 8 WAE. Weed density and aboveground biomass data were determined at 8 WAE by counting and collecting each weed species in two 0.25-m2 quadrats placed at two random locations in each plot. Each weed within the quadrat was cut at the soil surface and placed into separate paper bags by species. The weed biomass was dried in a kiln and the weights were recorded. The natural weeds included common lambsquarters, redroot pigweed, and foxtail species. Corn yield data were collected at harvest maturity using a mechanical small plot combine, and weight and moisture were recorded for each plot. Corn yield was then adjusted to 15.5% moisture before statistical analysis.
Data were analyzed using the GLIMMIX procedure, a mixed model analysis of variance, with SAS software (v.9.4; SAS Institute Inc, Cary, NC). Data from all six site-years were combined for analysis to allow for interpretation across multiple environments. The fixed effect was herbicide treatment and random effects were environment, treatments in different environments, and replications in each environment. One environment was removed for redroot pigweed analysis and three were removed for foxtail species analysis due to low weed density. One outlier, likely due to human error, was removed. Analysis for normality and determination of the best transformation for the data to fit a normal distribution was assessed through distribution plot, residual plots, and a Shapiro-Wilk test. Weed control data used an arcsine transformation, while weed density and biomass used a lognormal transformation. Corn yield was normal, and no transformation was necessary. Least square means and Tukey-Kramer tests were used to establish significance and treatment differences with a P-value of 0.05. All data were back-transformed for presentation of results. Expected visible weed control values were calculated using Colby’s equation:
$${\rm E = (X + Y) - (XY)/100} $$
where E is the expected percent control of the herbicide combination, X is the percent control of herbicide 1 at a particular rate, and Y is the percent control of herbicide 2 at a particular rate. A modified version of Colby’s equation was used to calculate expected values for density, biomass, and yield data, E = X*Y/untreated control, which are not on a 0 to 100 scale. Expected values were subject to the same transformations according to evaluation type. A t-test was performed to establish significance (P < 0.05) between observed and expected values.
Results and Discussion
Corn Injury
Pyroxasulfone (90, 120, and 150 g ai ha−1), saflufenacil (56, 75, and 95 g ai ha−1), and encapsulated saflufenacil + pyroxasulfone (146, 195, and 245 g ai ha−1) applied preemergence caused no visible corn injury at 1, 2, and 4 WAE (data not presented). This was not surprising since pyroxasulfone and the suspension concentrate formulation of saflufenacil are registered for application to corn before it emerges (OMAFRA 2021). Previous research on saflufenacil applied preemergence to corn reported minimal corn injury (Soltani et al. Reference Soltani, Shropshire and Sikkema2009) and field corn has excellent tolerance to pyroxasulfone with no, low, or transient corn injury (Geier et al. Reference Geier, Stahlman and Charvat2009; Knezevic et al. Reference Knezevic, Datta, Scott and Charvat2009; Stephenson et al. Reference Stephenson, Bond, Griffin, Landry, Wollam, Edwards and Hardwick2017).
Common Lambsquarters Control
When assessed at 8 WAE, pyroxasulfone applied at 90, 120, and 150 g ai ha−1 controlled common lambsquarters by 22%, 23%, and 30%, respectively; while saflufenacil applied at 56, 75, and 95 g ai ha−1 controlled the weed by 21%, 31%, and 35%, respectively (Table 2). The premixture of encapsulated saflufenacil + pyroxasulfone applied at 146, 195, and 245 g ai ha−1 provided 44%, 52%, and 60% control, respectively. Control at 4 WAE followed a similar trend. Encapsulated saflufenacil + pyroxasulfone at 245 g ai ha−1 provided greater common lambsquarters compared to pyroxasulfone (150 g ai ha−1) or saflufenacil (95 g ai ha−1) applied alone. Encapsulated saflufenacil + pyroxasulfone at 195 or 245 g ai ha−1 provided greater common lambsquarters control than pyroxasulfone (120 or 150 g ai ha−1) applied alone but similar to that of saflufenacil (75 or 95 g ai ha−1) applied alone at 8 WAE. S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1) controlled common lambsquarters by 95% and 94% at 4 and 8 WAE, respectively, which is greater than that provided by encapsulated saflufenacil + pyroxasulfone.
Table 2. Influence of encapsulated saflufenacil + pyroxasulfone on common lambsquarters control at 4 and 8 wk after application, and density and biomass of corn from six trials conducted in Ontario, Canada in 2022 and 2023. a – e
a Abbreviation: WAE, weeks after emergence.
b Means followed by the same letter are not significantly different according to the Tukey-Kramer multiple range test (P < 0.05).
c Expected values were calculated using Colby’s equation.
d Control data were back-transformed from arcsine transformation; density and biomass data were back-transformed from log transformation.
e Values in bold indicate a significant interaction of P < 0.05 (synergism when observed > expected; antagonism when observed < expected).
Common lambsquarters density and biomass data were variable due to uneven population counts. Pyroxasulfone applied at 90, 120, and 150 g ai ha−1 reduced common lambsquarters density by 43%, 59%, and 57%, respectively; while saflufenacil applied at 56, 75, and 95 g ai ha−1 reduced common lambsquarters density by 49%, 67%, and 65%, respectively (Table 2). Density was reduced by 80%, 78%, and 80% when encapsulated saflufenacil + pyroxasulfone was applied at 146, 195, and 245 g ai ha−1, respectively. Pyroxasulfone applied at 90, 120, and 150 g ai ha−1 reduced common lambsquarters biomass by 0%, 0%, and 19%, respectively; while biomass was reduced by 0%, 22%, and 25%, when saflufenacil was applied at 56, 75, and 95 g ai ha−1, respectively. Encapsulated saflufenacil + pyroxasulfone applied at 146, 195, and 245 g ai ha−1 reduced the weed biomass by 24%, 51%, and 8%, respectively. S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1) reduced common lambsquarters density and biomass by 98% and 97%, respectively, which was greater than all evaluated rates of encapsulated saflufenacil + pyroxasulfone.
The low level of common lambsquarters control obtained with pyroxasulfone in this study is similar to the 7% reported by Belfry et al. (Reference Belfry, McNaughton and Sikkema2015) at 4 wk after an application of pyroxasulfone at 150 g ai ha−1. Similarly, Yamaji et al. (Reference Yamaji, Honda, Kobayashi, Hanai and Inoue2014) reported lower common lambsquarters control with pyroxasulfone compared to other small-seeded broadleaf weeds such as redroot pigweed and black nightshade (Solanum nigrum L.). Common lambsquarters control with saflufenacil in this study was low, but Boydston et al. (Reference Boydston, Felix and Al-Khatib2012), Geier et al. (Reference Geier, Stahlman and Charvat2009), and OMAFRA (2021) reported control of common lambsquarters with saflufenacil. The encapsulated formulation used in this study may have resulted in reduced control. Control was low with the encapsulated form of saflufenacil + pyroxasulfone used in this study, but previous research with other Group 15 and Group 14 herbicide mixtures reported >80% control (Belfry et al. Reference Belfry, McNaughton and Sikkema2015; Mahoney et al. Reference Mahoney, Shropshire and Sikkema2014). Mahoney et al. (Reference Mahoney, Shropshire and Sikkema2014) studied pyroxasulfone applied preemergence in a mixture with flumioxazin (Group 14) and observed >95% control of common lambsquarters. Another mixture of Group 15 + 14 herbicides, pyroxasulfone + sulfentrazone, applied preemergence, provided 83% to 95% control of the weed (Belfry et al. Reference Belfry, McNaughton and Sikkema2015).
Redroot Pigweed Control
When assessed 4 WAE, pyroxasulfone applied at 90, 120, and 150 g ai ha−1 controlled redroot pigweed by 55%, 66%, and 71%, respectively; while saflufenacil applied at 56, 75, and 95 g ai ha−1 provided 24%, 33%, and 41% control, respectively (Table 3). Encapsulated saflufenacil + pyroxasulfone applied at 146, 195, 245 g ai ha−1 provided 75%, 78%, and 87% control, respectively, at 4 WAE. For all herbicide treatments evaluated, a numeric decrease in redroot pigweed control was observed at 8 WAE. Encapsulated saflufenacil + pyroxasulfone and pyroxasulfone at the three rates evaluated provided similar redroot pigweed control; however, control with the premix was greater than with saflufenacil applied alone at 4 and 8 WAE. S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1) provided 98% and 92% control at 4 and 8 WAE, respectively which is similar to that provided by encapsulated saflufenacil + pyroxasulfone at 195 and 245 g ai ha−1.
Table 3. Influence of encapsulated saflufenacil + pyroxasulfone on redroot pigweed control (4 and 8 wk after application) and density and biomass of corn from six trials conducted in Ontario, Canada in 2022 and 2023. a – e
a Abbreviations: WAE, weeks after emergence.
b Means followed by the same letter are not significantly different according to the Tukey-Kramer multiple range test (P<0.05).
c Expected values calculated with Colby’s equation.
d Control data presented was back-transformed from arcsine transformation; density and biomass data presented was back-transformed from log transformation.
e Values in bold indicate a significant interaction of P < 0.05 (synergism when observed > expected; antagonism when observed < expected).
Redroot pigweed density was reduced by 55%, 70%, and 75%, when pyroxasulfone was applied at 90, 120, and 150 g ai ha−1, respectively; while density was reduced by 55%, 65%, and 80% when saflufenacil was applied at 56, 75, and 95 g ai ha−1, respectively (Table 3). The encapsulated form of saflufenacil + pyroxasulfone applied at 146, 195, and 245 g ai ha−1 reduced redroot pigweed density by 85%, 90%, and 95%, respectively. Encapsulated saflufenacil + pyroxasulfone and corresponding rates of pyroxasulfone and saflufenacil applied alone produced similar results in pigweed density. Redroot pigweed biomass was reduced by 31%, 79%, and 85% with applications of pyroxasulfone at 90, 120, and 150 g ai ha−1, respectively; while it was reduced by 43%, 24%, and 49% with applications of saflufenacil at 56, 75, and 95 g ai ha−1, respectively. Encapsulated saflufenacil + pyroxasulfone at 146, 195, and 245 g ai ha−1 reduced the weed’s biomass by 86%, 90%, and 94%, respectively. S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1) reduced both density and biomass by 95% and 99%, respectively, which was similar to that of all rates of encapsulated saflufenacil + pyroxasulfone.
There are numerous reports that pyroxasulfone provides control of redroot pigweed (Nurse et al. Reference Nurse, Sikkema and Robinson2011; OMAFRA 2021; Yamaji et al. Reference Yamaji, Honda, Kobayashi, Hanai and Inoue2014). Yamaji et al. (Reference Yamaji, Honda, Kobayashi, Hanai and Inoue2014) reported ≥95% redroot pigweed control at rates ≥32 g ai ha−1, while the results of this study demonstrated much lower levels of control. Nurse et al. (Reference Nurse, Sikkema and Robinson2011) reported that the required dose of pyroxasulfone to achieve a 90% reduction in redroot pigweed biomass was 93 g ai ha−1. At the highest rate of pyroxasulfone (150 g ai ha−1) evaluated in this study a 90% reduction in redroot pigweed biomass was not achieved. Saflufenacil also controls redroot pigweed (Boydston et al. Reference Boydston, Felix and Al-Khatib2012; Geier et al. Reference Geier, Stahlman and Charvat2009; OMAFRA 2021), but in this study, the encapsulated formulation may have reduced its activity. Pigweed species control provided by saflufenacil + pyroxasulfone applied preemergence at ≥80 g ai ha−1 was 100% at 4 wk after application (Mahoney et al. Reference Mahoney, Shropshire and Sikkema2014). In this study, encapsulated saflufenacil + pyroxasulfone provided 75% to 87% redroot pigweed control 4 WAE.
Foxtail Species Control
When assessed at 4 WAE, pyroxasulfone applied at 90, 120, and 150 g ai ha−1 controlled foxtail species by 28%, 33%, and 51%, respectively; while saflufenacil applied at 56, 75, and 95 g ai ha−1 provided 10%, 12%, and 12% control, respectively (Table 4). Encapsulated saflufenacil + pyroxasulfone applied at 146, 195, 245 g ai ha−1 provided 35%, 43%, and 45% control, respectively. There was a numeric decrease in foxtail species control at 8 WAE with all herbicide treatments. Encapsulated saflufenacil + pyroxasulfone and pyroxasulfone at the three corresponding rates provided similar foxtail species control; however, control with the premix was generally greater both at 4 and 8 WAE than with saflufenacil applied alone. S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1) provided 47% and 25% control of foxtail species at 4 and 8 WAE, respectively, which was similar to that of encapsulated saflufenacil + pyroxasulfone at all rates.
Table 4. Influence of encapsulated saflufenacil + pyroxasulfone applied preemergence on foxtail species control (4 and 8 weeks after application), density, and biomass in corn from six trials conducted in Ontario, Canada in 2022 and 2023.
a Abbreviations: WAE, weeks after emergence.
b Means followed by the same letter are not significantly different according to the Tukey-Kramer multiple range test (P<0.05).
c Expected values calculated with Colby’s equation.
d Control data presented was back-transformed from arcsine transformation; density and biomass data presented were back-transformed from log transformation.
e Values in bold indicate a significant interaction of P < 0.05 (synergism when observed > expected; antagonism when observed < expected).
Pyroxasulfone applied at 90, 120, and 150 g ai ha−1 reduced foxtail species density by 70%, 85%, and 81%, respectively; while saflufenacil applied at 56, 75, and 95 g ai ha−1 reduced foxtail species density by 55%, 59%, and 47%, respectively (Table 4). Encapsulated saflufenacil + pyroxasulfone applied at 146, 195, and 245 g ai ha−1 reduced density by 74%, 62%, and 78%, respectively. Pyroxasulfone applied at 90, 120, and 150 g ai ha−1 provided biomass reductions of 27%, 68%, and 55%, respectively; while saflufenacil applied at 56, 75, and 95 g ai ha−1 provided reductions of 23%, 12%, and 4%, respectively. Encapsulated saflufenacil + pyroxasulfone applied at 146, 195, and 245 g ai ha−1 reduced biomass by 20%, 4%, and 58%, respectively. S-metolachlor/atrazine/mesotrione/bicyclopyrone (2,026 g ai ha−1) reduced density and biomass 64% and 11%, respectively. All rates of encapsulated saflufenacil + pyroxasulfone provided reductions in density and biomass that were similar to those of S-metolachlor/atrazine/mesotrione/bicyclopyrone.
Control of foxtail species at 8 WAE in this study was 15% to 36% when pyroxasulfone was used (Table 4); in contrast, Nurse et al. (Reference Nurse, Sikkema and Robinson2011), Yamaji et al. (Reference Yamaji, Honda, Kobayashi, Hanai and Inoue2014), and OMAFRA (2021) reported >80% control when pyroxasulfone was applied at similar rates. This may be due to rainfall and weed density variability between the two experimental sites in this study. Saflufenacil is known to provide limited control of grass weeds, including foxtail species (Boydston et al. Reference Boydston, Felix and Al-Khatib2012; Jhala et al. Reference Jhala, Ramirez and Singh2013; OMAFRA 2021), which supports the data reported in this study. Saflufenacil + pyroxasulfone applied preemergence at 240 g ai ha−1 provided 98% control of green foxtail control at 4 wk after application (Mahoney et al. Reference Mahoney, Shropshire and Sikkema2014), whereas encapsulated saflufenacil + pyroxasulfone applied at a similar rate (245 g ai ha−1) provided 44% control at 4 WAE in the current study (Table 4).
Corn Yield
Weed interference reduced corn yield by 45% in this study (Table 5). Corn yield was reduced by 30% to 38% and by 34% to 37%, with pyroxasulfone and saflufenacil, respectively, similar to that of the untreated control. Corn yield was also reduced by 24%, 22%, and 18% after preemergence applications of encapsulated saflufenacil + pyroxasulfone at 146, 195, and 245 g ai ha−1, respectively, compared with the weed-free control. Applications of S-metolachlor/atrazine/mesotrione/bicyclopyrone to reduce weed interference resulted in a 6% decrease in corn yield. Corn yields after applications of pyroxasulfone, saflufenacil, and encapsulated saflufenacil + pyroxasulfone were similar, and corn yields were similar after applications of encapsulated saflufenacil + pyroxasulfone and S-metolachlor/atrazine/mesotrione/bicyclopyrone. Corn yields were similar to that of the untreated control with applications of pyroxasulfone (90, 120, and 15 g ai ha−1), saflufenacil (56, 75, and 95 g ai ha−1), and encapsulated saflufenacil + pyroxasulfone (146 and 195 g ai ha−1). Reduced weed interference after applications of encapsulated saflufenacil + pyroxasulfone (195 and 245 g ai ha−1) and S-metolachlor/atrazine/mesotrione/bicyclopyrone resulted in corn yields that were similar to the weed-free control.
Table 5. Influence of encapsulated saflufenacil + pyroxasulfone herbicide mixtures on corn yield. a,b,c
a Means followed by the same letter are not significantly different according to the Tukey-Kramer multiple range test (P < 0.05).
b Expected values calculated using Colby’s equation.
c Values in bold indicate a significant interaction of P < 0.05 (synergism when observed > expected; antagonism when observed < expected).
Interaction of Pyroxasulfone and Encapsulated Saflufenacil
When assessing the interaction between pyroxasulfone and saflufenacil, nonsignificant results indicate an additive interaction, while significant results indicate a synergistic response if the observed value is greater than expected, or antagonistic if the observed value is less than expected. Visible control data showed the interaction of encapsulated saflufenacil + pyroxasulfone was additive for controlling common lambsquarters, redroot pigweed, and foxtail species with two exceptions. Redroot pigweed control at 8 WAE had a synergistic response when encapsulated saflufenacil + pyroxasulfone was applied at 146 g ai ha−1 (Table 3) and one instance of antagonism was recorded at 4 WAE for visible foxtail species control when encapsulated saflufenacil + pyroxasulfone was applied at 245 g ai ha−1 (Table 4). Density and biomass data indicated an additive interaction with only one exception, an antagonistic response by foxtail species when encapsulated saflufenacil + pyroxasulfone was applied at 195 g ai ha−1. The interaction of pyroxasulfone and saflufenacil on yield was additive at all rates (146, 195, and 245 g ai ha−1) of encapsulated saflufenacil + pyroxasulfone (Table 5).
Even though there were some contradictions, the overall interaction between encapsulated saflufenacil + pyroxasulfone is additive. All synergistic or antagonistic responses for density and biomass can be attributed to experimental variability. Previous research conducted by Tidemann et al. (Reference Tidemann, Hall, Johnson, Beckie, Sapsford, Willenborg and Raatz2014) and Ferrier et al. (Reference Ferrier, Soltani, Hooker, Robinson and Sikkema2022) established the interaction between the Group 15 + 14 herbicide combinations of pyroxasulfone + sulfentrazone and pyroxasulfone + flumioxazin, respectively was additive, thereby supporting the findings of this study.
In conclusion, differences in control of weeds with pyroxasulfone, saflufenacil, and encapsulated saflufenacil + pyroxasulfone were specific to the weed species and herbicide rate. Common lambsquarters control was improved when encapsulated saflufenacil + pyroxasulfone was applied at 245 g ai ha−1 over either pyroxasulfone (150 g ai ha−1) or saflufenacil (95 g ai ha−1) applied alone. Redroot pigweed and foxtail species control was improved with applications of encapsulated saflufenacil + pyroxasulfone (146, 195, 245 g ai ha−1) compared to corresponding rates of saflufenacil (56, 75, 95 g ai ha−1). Corn yields were similar for each active ingredient, pyroxasulfone and saflufenacil, applied alone and in combination. Weed control, density, biomass, and corn yield data indicated an additive interaction between pyroxasulfone and saflufenacil, with a few indications of synergism and antagonism.
Practical Implications
Weed control differences with pyroxasulfone, saflufenacil, and the encapsulated saflufenacil + pyroxasulfone formulation were dependent on the weed species and herbicide application rates. Data on weed control, density, and biomass, and corn yield showed an additive interaction between pyroxasulfone and saflufenacil, with occasional indications of synergistic and antagonistic effects. The new formulation of encapsulated saflufenacil + pyroxasulfone offers another weed option in corn production. The combination of these two herbicides provides control of a broader spectrum of weeds without causing corn injury. Additionally, the additive interaction between saflufenacil and pyroxasulfone suggests that the co-application of these herbicides can enhance weed control, resulting in corn yields that are comparable to those when the current industry standard herbicide is used. This formulation could be a valuable tool for farmers seeking to improve weed management while maintaining high crop productivity, especially in areas with diverse weed populations.
Acknowledgments
We thank Kris McNaughton for providing technical assistance.
Funding statement
This project was funded in part by BASF Canada Inc.
Competing Interests
Chris Budd is senior biologist with BASF Canada Inc. The other authors declare they have no conflicts of interest.
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