Commercial immunoassay-based test kits are widely used for rapid screening of deoxynivalenol (DON) in maize; however, inconsistent results are frequently observed under commercial testing conditions. This study evaluated two distinct contributors to such variability: analytical cross-reactivity of commercial DON immunoassays and between-site variability arising from routine grain elevator testing practices. Under controlled laboratory conditions, all kits accurately measured DON but responded differently to co-occurring DON derivatives. In naturally contaminated maize, immunoassay results reflected the combined presence of DON and co-occurring derivatives, consistent with differences in antibody specificity. An interlaboratory comparison involving multiple grain elevators analyzing identical blinded samples demonstrated substantial between-site variability in reported DON concentrations, with about 16% of results deviating by more than ±20% from the LC–MS/MS reference value. Collectively, these findings show that inconsistent DON test outcomes arise from the combined effects of antibody cross-reactivity and site-specific testing variability, rather than from any unreliability of the analytical methods themselves. This finding highlights the importance of interpreting rapid DON measurements considering these factors.

Context: The impact of nitrogen fertilizer (N) application timing on nitrous oxide (N2O) emissions is inconsistent in the literature. This inconsistency is attributed to year-to-year weather variations, which affect soil conditions around N application time. Planting dates (PD) also vary year-to-year based on weather, and PD can influence N timing decisions. Objective: The study aims to evaluate: i) the long-term effects of different N application timings on N2O emissions and, ii) how variations in PD influence the relative performance of different N timing strategies. Methods: We used the DeNitirifcation-DeComposition (DNDC) model, calibrated with field measurements from Elora, Ontario, Canada, to simulate 39 growing seasons using historical weather data. Three N timing strategies were tested: spring application one day before planting, in-season application at the V6 growth stage, and a splitN strategy with N applied at both times. PDs were either dynamically adjusted each year based on rainfall or fixed to one of three typical corn (Zea mays L.) planting dates in Ontario: April 25, May 5, and May 15. Results: For the first objective, the long-term simulation found that average N2O emissions were greatest when N was applied at V6 (3.2 kg N ha-1) compared to when N was applied pre-plant (2.3 kg N ha-1) or split-applied (2.0 kg N ha-1). This was caused by slightly greater rainfall around V6 than planting. For the second objective, the relative performance of different N-timing strategies was affected by PD. Earlier PDs resulted in lower N2O emissions compared to later PDs, primarily due to lower soil temperatures around the time of N fertilizer application. Earlier PDs also led to the largest differences in N2O emissions among the N timing strategies, with PD delays leading to smaller differences among N timing strategies. Conclusions: Large single N applications, particularly those applied in-season, resulted in greater N2O emissions than split and at-planting N applications in a long-term simulation. Early PDs consistently reduced N2O emissions by creating less favourable conditions for N2O production. Moreover, the relative performance of N timing strategies was mediated by PD. Implications: This study highlights the interconnected nature of cropping systems, where one management practice, PD, can influence a seemingly unrelated outcome, N2O emissions. Long-term climatic, social, economic, and technological changes that influence PD will also influence N2O emissions from spring and summer-applied N fertilizer.

Conservation tillage and crop rotation diversification have been promoted to increase soil C and N storage; however, the interactive effects of tillage and crop rotation on soil C and N dynamics remain contradictory. Using a long-term (24 years) experiment established at a clay loam site (Orthic Humic Gleysol) at Ridgetown, Ontario, Canada, the interactive effects of five crop rotations and two tillage systems were tested on soil organic C (SOC) and total N storage in soil depth increments and in the full soil profile (0-0.6 m) in 2019. While crop rotation influenced SOC and total N concentration in top 0.2 m, these effects were minimized when storage was expressed on an equivalent soil mass basis. Over the 0-0.6 m depth, no-tillage had 24 Mg SOC ha-1 and 4.7 Mg total N ha-1 greater content, respectively, than conventional tillage, supporting the value of no-tillage on increasing soil C and N in the long-term. Interestingly, no interactive effects of crop rotation and tillage on soil C and N storage in 0-0.6 m were observed. While the type of crop species and amount of C and N inputs under different crop rotations are important variables impacting the soil C and N storage, our results suggest that the crop rotation diversity was not a major driver of soil C and N in this study. Future mechanistic investigations exploring the persistence and linkage of soil C and N with crop rotation diversity in the tested production systems are needed.

Low-temperature flooding and ice encasement (LTFIE) cause variable survival of winter wheat ( Triticum aestivum L.) in Ontario, which limits the adoption of wheat into crop rotations by growers. The development of novel cultivars capable of withstanding LTFIE is a promising avenue for improvement, but the methods used to assess the survival of winter wheat under LTFIE are restricted. This study developed updated methods to determine the survival of wheat cultivars under LTFIE using controlled environments and, to our knowledge, is the first method since the 1980s to use Canadian eastern soft red winter wheat (CESRW) to conduct cold tolerance studies. Chamber-acclimated plants of AC Carberry (spring wheat control), Branson (CESRW), CM614 (CESRW), and Norstar (hardy Canadian western red winter control) cultivars were used to estimate the days (LD50) and temperature (LT50) to reach 50% mortality under ice and without ice treatments. Norstar had the longest LD50 at 33 days, Branson and CM614 had similar LD50 of 18 and 20 days, and AC Carberry did not reach an LD50 as it died early in both treatments. The LT50 of each cultivar was different; Norstar had the lowest LT50 (−13.6 °C day 0 and −13.2 °C day 7), and AC Carberry had the highest LT50 (−6.6 °C day 0 and −2.7 °C day 7). The detailed methods developed in this study were more reliable compared to older methods based on the more accurate reported LD50 and LT50 of the cultivars, therefore, these methods can be used to screen winter cereals for LTFIE in the future.

In agricultural ecosystems, soil organic carbon (SOC) which is affected by management practices, is important for soil health, food security, and climate change mitigation. However, accurately assessing the influence of agricultural management practices on SOC storage is a challenge, due in part to the uncertainty of calculation approaches used to estimate SOC stocks. Although equivalent soil mass (ESM) is widely recommended over the fixed depth (FD) approach, few field studies directly compare FD with different ESM approaches. Hence, the magnitude of potential difference in estimated SOC stocks among different approaches is not well known. Here, we collected soil cores (0–60 cm depth) from a 24-yr experiment (Ridgetown, Ontario, Canada) to investigate (1) the effect of two tillage systems (conventional tillage: CT, moldboard plowing to ∼20 cm deep; no-tillage with zone tillage: NT/ZT) on different SOC estimates (n=448), including concentration and stocks estimated by FD and ESM (cubic spline interpolation model: ESMcubic_spline, linear interpolation model: ESMlinear, and non-modeling fit: ESMnon_model); and (2) the relative difference of SOC stocks estimated by FD and ESM under NT/ZT system. The tillage effect on SOC stock was more pronounced than SOC concentration (P<0.05; except for 0–5 cm depth), indicating that using SOC concentration alone appears to be unreliable for evaluating tillage system effects on carbon sequestration. Furthermore, FD overestimated SOC stocks under NT/ZT (P<0.05), mainly due to greater soil bulk density than CT (P<0.05). Specifically, in the 0–60 cm depth, FD overestimated about 15% (or 30.6 Mg ha−1) of cumulative SOC stocks than ESMcubic_spline. However, the differences in SOC stocks estimated among three ESM approaches (ESMcubic_spline, ESMlinear, and ESMnon_model) were negligible (P>0.05; Cohen’s d<0.2), suggesting that these approaches may work equally well when soil depth increment is small (< 10 cm). Overall, we recommend using the ESM approach to calculate SOC stock, especially when comparing treatments where soil bulk density varies. Our findings may help to guide policy decision-making towards more accurately quantifying SOC stock when considering climate change mitigation practices.

Growing multiple crops in rotation can increase the sustainability of agricultural systems and reduce risks from increasingly adverse weather. However, widespread adoption of diverse rotations is limited by economic uncertainty, lack of incentives, and limited information about long-term outcomes. Here, we combined 36,000 yield observations from 20 North American long-term cropping experiments (434 site-years) to assess how greater crop diversity impacts productivity of complete rotations and their component crops under varying growing conditions. Maize and soybean output increased as the number of species and rotation length increased, while results for complete rotations varied by site depending on which crops were present. Diverse rotations reduced rotation-level output at eight sites due to the addition of lower-output crops such as small grains, illustrating trade-offs. Diverse rotations positively impacted rotation-level output under poor growing conditions, which illustrates how diverse cropping systems can reduce the risk of crop loss in a changing climate.

Fusarium graminearum is the most important pathogen of maize and winter wheat in Canada, resulting in yield loss and mycotoxin contamination. Fungicides are essential to manage F. graminearum in cereal crops. Until pydiflumetofen became commercial, the only available fungicides were triazoles, limiting the potential to manage fungicide resistance. Fusarium graminearum isolates were surveyed from wheat, grain maize and overwintering maize stalks in southern Ontario. Chemotype and the baseline sensitivity to pydiflumetofen were determined in addition to sensitivity to common fungicides used to control F. graminearum. Fusarium graminearum has several strains producing different trichothecenes called chemotypes. In Ontario, 73.3% of the F. graminearum isolates were 3ANX chemotypes producing 7 alpha-hydroxy, 15-deacetylcalonectrin, in addition to 15-acetyldeoxynivalenol and deoxynivalenol; the remaining isolates were 15ADON chemotypes producing only 15-acetyldeoxynivalenol and deoxynivalenol. Chemotype was not affected by isolate source (wheat grain, maize grain, maize stalks) nor by location. All isolates were sensitive to pydiflumetofen and fungicide products containing pydiflumetofen. The mean EC50 for isolates exposed to pydiflumetofen was 0.05 mu g mL-1 (range 0.01-0.10 mu g mL-1). The mean EC50 for isolates exposed to Miravis (R) Ace (containing pydiflumetofen and propiconazole), Miravis (R) Neo 300SE (containing pydiflumetofen, azoxystrobin and propiconazole), Caramba (R) (containing metconazole), Proline (R) (containing prothioconazole) and Prosaro (containing prothioconazole and tebuconazole) was 0.06, 0.13, 0.18, 0.05, 3.75 and 0.30 mu g mL-1, respectively. These data will be useful in monitoring the development of fungicide resistance.

Waterhemp is a summer annual, broadleaf weed with high fecundity, short seed longevity in the soil, and wide genetic diversity. Populations have evolved resistance to five herbicide modes of action (Groups 2, 5, 9, 14, and 27), which are present across southern Ontario; this has increased the challenge of controlling this competitive weed species in corn, the most important grain crop produced worldwide and the highest-value agronomic crop in Ontario. Acetochlor is a Group 15 soil-applied residual herbicide that has activity on many grass and broadleaf weeds but has yet to be registered in Canada. The objective of this study was to ascertain whether mixtures of acetochlor with flumetsulam, dicamba, atrazine, isoxaflutole/diflufenican, or mesotrione + atrazine applied preemergence would increase the control of multiple-herbicide-resistant (MHR) waterhemp in corn. Five field trials were conducted between 2022 and 2023. No corn injury was observed. Acetochlor applied alone controlled MHR waterhemp 97% 12 wk after application (WAA). All herbicide mixtures controlled MHR waterhemp similarly at >= 98% 12 WAA; there were no differences among herbicide mixtures. Flumetsulam, dicamba, and atrazine provided lower MHR waterhemp control than all other herbicide treatments and did not reduce density or biomass. Acetochlor reduced waterhemp density 98%, while the acetochlor mixtures reduced density similarly at 99% to 100%. This study concludes that the acetochlor mixtures evaluated provide excellent waterhemp control; however, control was not greater than acetochlor alone. Herbicide mixtures should be used as a best management practice to mitigate the evolution of herbicide resistance.

The stability of a trait refers to the extent to which its expression in a given genotype varies across environments. The more stable a trait, the less variable its expression. Grain yield stability is a central consideration in corn production to ensure that hybrids perform consistently across environments and is frequently quantified given its importance. Little attention has been paid to the stability of corn yield components, kernel number per m2 (KN), and kernel weight (KW). Our hypothesis is that while previous research suggests that yield stability of commercial corn hybrids is generally consistent, the stabilities of KN and KW may exhibit significant differences, even when overall yield stability remains constant. This study evaluated the yield and yield component stabilities of 23 commercial corn hybrids conducted on-farm at five location-years in Ontario, Canada, using Finlay-Wilkinson regression. Most (61%) hybrids exhibited average yield stability with beta 1-values close to 1.0. But seven hybrids displaying average yield stability had KN and/or KW stabilities significantly different than average. While in absolute terms, KW was always more stable than KN across environments, the data indicate that hybrids have different mechanisms to achieve stable yields in terms of relative yield component adjustments. Overall, 14 hybrids had yield component beta 1-values significantly more or less stable than average. The instances where yield component beta 1-values differed significantly from 1.0 were almost equally divided between KN and KW. These findings support the potential for hybrid-specific corn management, that is, tailoring management practices to take advantage of hybrid variation in yield component stabilities. The stability of yield components (kernel number per m2 [KN] and kernel weight [KW]) are not commonly studied. For hybrids with similar yield stability values, stabilities of yield components (KN and KW) could differ. Differences in yield component stabilities may explain existing findings of hybrid-specific response to management. Larger datasets with replications within sites should be used to validate these findings in a wider range of hybrids.

Waterhemp has evolved resistance to seven herbicide modes of action in the United States and to five in Canada, which limits weed control options for producers. The objective of this research was to quantify the level and duration of residual control of multiple herbicide-resistant (MHR) waterhemp with five Group 15 herbicides (acetochlor, dimethenamid-p, flufenacet, pyroxasulfone, and S-metolachlor) applied preemergence in a non-crop area. Four field trials were conducted over a 2-yr period (2021, 2022) in southwestern Ontario, Canada. By 4 wk after application (WAA) 91% of waterhemp had emerged in the nontreated control area. The numerical control of waterhemp with all Group 15 herbicides, with the exception of pyroxasulfone, was greatest at 4 WAA, then control declined. Flufenacet provided the lowest waterhemp control; dimethenamid-p and S-metolachlor provided intermediate control, and acetochlor and pyroxasulfone provided the highest control. Waterhemp control with pyroxasulfone peaked at 6 WAA with 99% and declined to 77% at 12 WAA. Flufenacet (low and high rates) was predicted to reduce waterhemp emergence by 50% for 42 to 44 d after application (DAA). Dimethenamid-p, S-metolachlor, and acetochlor (both formulations and three rates) were predicted to reduce waterhemp emergence by 80% for 36, 43, and 33 to 51 DAA, respectively; in contrast, pyroxasulfone was predicted to reduce waterhemp emergence by 80% for 82 DAA. This study concludes that of the Group 15 herbicides evaluated, flufenacet provides the lowest and shortest residual control of waterhemp, and pyroxasulfone provides the highest and longest residual control of waterhemp.

Documented 6-way (Groups 2, 4, 5, 9, 14, and 27) and 5-way (Groups 2, 5, 9, 14, and 27) multiple-herbicide-resistant (MHR) waterhemp have been confirmed in the US and Canada, respectively causing corn and soybean yield losses > 70%. The objective of this study was to determine the effect of acetochlor application timing and rate on non-emerged MHR waterhemp control in corn and soybean. Acetochlor is not yet registered in Canada, but it could be useful component of an integrated MHR waterhemp control program. Two studies, one in corn and one in soybean, were conducted in southwestern Ontario, Canada from 2020 to 2022. Three rates of acetochlor were applied preplant (PP), preemergence (PRE) and postemergence (POST) to non-emerged waterhemp. In corn, acetochlor [Emulsifiable Concentrate (EC)] applied at 1,225, 2,100 and 2,950 g ai ha-1 controlled MHR waterhemp 81, 85, and 90%, respectively, at 8 weeks after POST application (WAC). Acetochlor EC applied POST or PRE provided better control than when applied PP at 4, 8, and 12 WAC. In soybean, acetochlor [Capsule suspension (CS)] applied at 1,050, 1,375, and 1,700 g ai ha-1 controlled MHR waterhemp 63, 70, and 74%, respectively, at 8 WAC. The timing of acetochlor CS application did not affect MHR waterhemp control. Acetochlor applied at the low, medium, and high rate reduced waterhemp density by 87, 89, and 92% in corn, and by 82, 84, and 87% in soybean, respectively. The high rate of acetochlor provides acceptable control of MHR waterhemp in corn; control in soybean was inadequate.

Herbicides are often used to terminate cover crops. Producers would like to use herbicides that work quickly, are effective, and do not increase the risk of selecting herbicide-resistant weeds. Eight experiments were conducted to determine whether mixing glyphosate (900 g a.e. ha(-1)) with rimsulfuron (15 g a.i. ha(-1)), mesotrione (100 g a.i. ha(-1)), or rimsulfuron + mesotrione enhances winter rye control and to ascertain whether using urea ammonium nitrate (UAN) as the herbicide carrier improves and accelerates herbicide efficacy. Winter rye control was assessed 1, 2, 3, and 4 wk after application (WAA) and biomass was measured 4 WAA. The addition of rimsulfuron, mesotrione, or rimsulfuron + mesotrione to glyphosate did not enhance winter rye control. Similarly, using UAN as the herbicide carrier did not improve or accelerate herbicide efficacy. Glyphosate alone provided the greatest level of winter rye control. The addition of rimsulfuron, mesotrione, or rimsulfuron + mesotrione to glyphosate did not increase the level or speed of control. However, mixing glyphosate with rimsulfuron, mesotrione, or rimsulfuron + mesotrione adds other modes of action without compromising winter rye control.

Physical fractions of soil organic matter (SOM) are established indicators of management-induced change and have been used to estimate the soil carbon storage capacity and storage potential. Here, we use SOM physical fractions and soil textures to identify management practices that maintain or enhance soil health and carbon storage in agricultural soils in Ontario. Metadata from the National Soil Database were used to estimate carbon storage potentials and calculate carbon deficits. A map was created showing carbon deficits in Ontario's agricultural soils and indicates that these soils have the potential to store an additional 0 to 2 kgm(-2) in the top 20cm of the soil. Tillage system generally had no effect on the size of the carbon deficit at four long-term agricultural experiments (Delhi, Elora, Ottawa, and Ridgetown). There was only a significant tillage effect at Ridgetown and only in the maize-soybean crop rotation, where the carbon deficit was 2.95 g C kg soil(-1) under conventional tillage compared to 8.97 g C kg soil(-1) with no tillage. A statistically significant effect of crop rotation was detected in Elora and Ridgetown. In Elora, continuous alfalfa had the smallest carbon deficit (7.25 g C kg soil(-1)) and maize-soybean rotation had the largest deficit (12.07 g C kg soil(-1)). In Ridgetown, themaize-soybean rotation had the smallest carbon deficit (2.95 g C kg soil(-1)). Regression analysis showed a weak negative relationship (R-2= 0.11; P < 0.001) between carbon storage deficits and soil health scores. This suggests that increasing SOM levels alone may not improve soil health.

Weed interference from glyphosate/glufosinate-resistant (GGR) volunteer corn can reduce soybean yield and quality. The recent release of glyphosate/glufosinate/2,4-D choline (GG2)-resistant soybean will allow for expanded POST herbicide mixture options for broad-spectrum weed control. Herbicide antagonism between ACCase-inhibiting graminicides and synthetic auxin herbicides has been confirmed for various grass weed species, including volunteer corn. Field experiments (total of 4) were carried out in 2021 and 2022 in southwestern Ontario to assess volunteer corn control with combinations of glufosinate, 2,4-D choline, or dicamba plus clethodim or quizalofop-p-ethyl applied POST to GG2-resistant soybean. Quizalofop-p-ethyl and quizalofop-p-ethyl + glufosinate controlled GGR volunteer corn 95 and 98%, respectively, 6 weeks after application (WAA); adding 2,4-D choline or dicamba to quizalofop-p-ethyl reduced control to ≤ 15%. Clethodim controlled GGR volunteer corn 81%, and the addition of glufosinate increased control to 97%; the co-application of 2,4-D choline or dicamba with clethodim reduced GGR volunteer corn control to 58 and 45%, respectively at 6 WAA. ACCase-inhibiting herbicides co-applied with glufosinate resulted in a synergistic improvement in GGR volunteer corn control while co-applications with synthetic auxin herbicides resulted in an antagonistic decrease in GGR volunteer corn control. Greater antagonism occurred when the synthetic auxin herbicides were co-applied with quizalofop-p-ethyl than clethodim. All mixtures of quizalofop-p-ethyl or clethodim with 2,4-D or dicamba resulted in unacceptable control of GGR volunteer corn.

Glyphosate-resistant (GR) biotypes of horseweed were first confirmed in southern Ontario in 2010 and have spread across southern Ontario. A total of four field experiments were conducted between 2021 and 2022 to determine GR horseweed control with one-and two-pass herbicide programs in glyphosate/glufosinate/2,4-D-resistant (GG2R) soybean. 2,4-D choline/glyphosate DMA, halauxifen-methyl, and saflufenacil applied preplant (PP) controlled GR horseweed by 59%, 72%, and 78% 8 wk after postemergence (POST) application (WAA-POST); there was no improvement of GR horseweed control when 2,4-D choline/glyphosate DMA was added to saflufenacil; in contrast, there was improved GR horseweed control when saflufenacil was added to 2,4-D choline/glyphosate DMA. Glufosinate and 2,4-D choline/glyphosate DMA applied POST controlled glyphosate-resistant horseweed by 71% and 86%, respectively, 8 WAA-POST. Two-pass herbicide programs of a PP followed by POST application provided greater GR horseweed control than a PP or POST herbicide applied alone. Glufosinate or 2,4-D choline/glyphosate DMA applied POST following 2,4-D choline/glyphosate DMA or halauxifen-methyl applied PP improved GR horseweed control by 29% to 38% and 24%, respectively at 8 WAA-POST. The application of 2,4-D choline/glyphosate DMA applied POST following saflufenacil applied PP improved control by 20% 8 WAA-POST; there was no improvement of GR horseweed control when glufosinate was applied POST following saflufenacil applied PP or when either POST herbicide was applied following saflufenacil + 2,4-D choline/glyphosate DMA applied PP. When used in a two-pass program, 2,4-D choline/glyphosate DMA POST provided 2% to 3% greater control of GR horseweed than glufosinate.

Objectives This report provides information about the public release of the 2018–2019 Maize G X E project of the Genomes to Fields (G2F) Initiative datasets. G2F is an umbrella initiative that evaluates maize hybrids and inbred lines across multiple environments and makes available phenotypic, genotypic, environmental, and metadata information. The initiative understands the necessity to characterize and deploy public sources of genetic diversity to face the challenges for more sustainable agriculture in the context of variable environmental conditions. Data description Datasets include phenotypic, climatic, and soil measurements, metadata information, and inbred genotypic information for each combination of location and year. Collaborators in the G2F initiative collected data for each location and year; members of the group responsible for coordination and data processing combined all the collected information and removed obvious erroneous data. The collaborators received the data before the DOI release to verify and declare that the data generated in their own locations was accurate. ReadMe and description files are available for each dataset. Previous years of evaluation are already publicly available, with common hybrids present to connect across all locations and years evaluated since this project’s inception.

Weed control efficacy with contact herbicides can depend on weed height at application. Four field experiments were conducted at sites with multiple weed species at different heights to determine the effect of weed height, glufosinate rate, and the addition of ammonium sulfate (AMS) on annual broadleaf weed control in soybean in southwestern Ontario, Canada, during 2021 and 2022. Glufosinate was applied at 300 or 500 g ai ha-1 without or with 6.50 L ha-1 of AMS to 5, 10, and 15 cm tall common lambsquarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.), velvetleaf (Abutilon theophrasti Medik.), and redroot pigweed (Amaranthus retroflexus L.). Glufosinate provided excellent common ragweed control (> 98%) at both rates, without and with AMS, and at all three heights 4 weeks application (WAA). In contrast, glufosinate efficacy declined when applied to common lambsquarters, velvetleaf, and redroot pigweed > 5 cm in height. The addition of AMS to glufosinate improved common lambsquarters control. Increasing the rate of glufosinate to 500 g ai ha-1 and the addition of AMS improved control of velvetleaf and redroot pigweed. The results of this study demonstrate that the effect of glufosinate rate, AMS addition, and weed height at application timing is weed species-specific. In general, glufosinate (300 g ai ha-1) controlled common annual broadleaf weeds if weeds were < 5 cm in height; otherwise, glufosinate needed to be applied at 500 g ai ha-1 with AMS for control of annual broadleaf weeds, especially common lambsquarters, velvetleaf and redroot pigweed.

The development of glufosinate-resistant soybean cultivars has created opportunities for use of glufosinate applied postemergence for weed control. Four field experiments were conducted in 2021 and 2022 to ascertain the effect of glufosinate rate and the addition of ammonium sulfate on annual weed control in glyphosate/glufosinate/2,4-D-resistant soybean. An increased glufosinate rate of 500 from 300 g ai ha(-1) improved control of common ragweed, common lambsquarters, redroot pigweed, and foxtail species and resulted in decreased density and dry biomass of common lambsquarters and foxtail species. The addition of ammonium sulfate to glufosinate increased control of common lambsquarters, 2 and 8 wk after application (WAA), and of foxtail species, 2, 4, and 8 WAA, but did not improve control of common ragweed and redroot pigweed. Increasing the dose of glufosinate from 300 to 500 g ai ha(-1) improves control of common ragweed, redroot pigweed, common lambsquarters, and foxtail species; however, the benefit of the addition of ammonium sulfate to glufosinate is weed species-specific.

Glyphosate + dicamba has provided variable glyphosate-resistant Canada fleabane (GRCF) control in glyphosate/dicamba-resistant (GDR) soybean. Previous research has indicated improved GRCF control when a third herbicide was added to glyphosate + dicamba, though research is limited. The objective of this research was to ascertain if the level and consistency of GRCF control can be improved when adding tiafenacil, metribuzin, bromoxynil, pyraflufen-ethyl/2,4-D, 2,4-D ester, halauxifen-methyl or saflufenacil to glyphosate + dicamba applied preplant (PP) in GDR soybean. Four field trials were conducted in 2020 and 2021 in commercial fields in southwestern Ontario, Canada. Glyphosate + dicamba controlled GRCF 57, 93 and 94% at 2, 4 and 8 WAA, respectively. Adding bromoxynil to glyphosate + dicamba improved GRCF control from 57 to 77% at 2 WAA; adding saflufenacil to glyphosate + dicamba improved GRCF control from 57 to 92, 93 to 99, and 94 to 99% at 2, 4 and 8 WAA, respectively. All three-way tank-mixtures improved the consistency of GRCF control, except for glyphosate + dicamba + 2,4-D ester at 2 WAA, glyphosate + dicamba + 2,4-D ester, tiafenacil or metribuzin at 4 WAA, and glyphosate + dicamba + tiafenacil or bromoxynil at 8 WAA. This study concludes that the level and consistency of GRCF control was improved when saflufenacil was added to a PP application of glyphosate + dicamba in soybean.

Glyphosate-resistant (GR) horseweed interference in soybean can reduce soybean yield up to 93%. Glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl or pyraflufen-ethyl/2,4-D applied preplant (PP) provide variable GR horseweed control in soybean. The objective of this study was to determine if the addition of saflufenacil or metribuzin to glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl, or pyraflufen-ethyl/2,4-D will improve the level and consistency of GR horseweed control. Four trials were conducted over the 2020 and 2021 field seasons in fields with GR horseweed populations. Glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl, or pyraflufen-ethyl/2,4-D controlled GR horseweed 96%, 77%, 71%, and 52%, respectively, at 8 wk after application (WAA). When saflufenacil or metribuzin was added to glyphosate plus dicamba or 2,4-D ester, GR horseweed control was not improved at 8 WAA. When saflufenacil or metribuzin was added to glyphosate plus halauxifen-methyl, GR horseweed control improved by 27% and 25%, respectively, at 8 WAA. When saflufenacil or metribuzin was added to glyphosate plus pyraflufen-ethyl/2,4-D, GR horseweed control was improved by 47% and 37%, respectively, at 8 WAA. The consistency of GR horseweed control was improved when saflufenacil or metribuzin was added to glyphosate plus dicamba, 2,4-D ester, halauxifen-methyl, or pyraflufen-ethyl/2,4-D compared to each herbicide applied alone. Synergism was observed when metribuzin was added to glyphosate plus halauxifen-methyl and when saflufenacil or metribuzin was added to glyphosate plus pyraflufen-ethyl/2,4-D at 8 WAA. Though GR horseweed control was improved with the addition of saflufenacil or metribuzin to glyphosate plus halauxifen-methyl or pyraflufen-ethyl/2,4-D, all treatments including saflufenacil resulted in the highest level and most consistent control.