Clethodim is an important herbicide for managing Texas panicum. However, its efficacy is influenced by the weed size and environmental stress during application. Therefore, field and greenhouse studies were conducted in 2023 and 2024 to evaluate clethodim efficacy on various Texas panicum sizes. Clethodim was applied at Texas panicum heights ranging from 5 cm to 60 cm. A sequential application was applied 2 wk after the initial treatment for larger weed sizes (15 to 60 cm). In separate field and greenhouse studies, nonionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), COC + ammonium sulfate (AMS), and MSO + AMS adjuvants were mixed with clethodim to determine efficacy on 10- to 15-cm and 20- to 30-cm Texas panicum. In the weed size study, sequential applications of clethodim increased Texas panicum control compared to a single application. At the 10- to 15-cm growth stage, a single application provided 90% Texas panicum control, whereas the sequential treatment improved control from 76% to 91% at the 15- to 20-cm growth stage. However, clethodim efficacy declined as Texas panicum size increased across single and sequential treatments. In the adjuvant studies, clethodim plus COC, COC + AMS, or MSO + AMS provided 91%, 93%, and 90% control at the 10- to 15-cm growth stage, respectively; however, efficacy decreased for 20- to 30-cm Texas panicum. Texas panicum efficacy was higher for clethodim plus MSO + AMS than clethodim plus MSO; however, AMS did not increase clethodim + COC efficacy. Overall, Texas panicum control with clethodim was most effective when weed height was 15 cm or less. A sequential application of clethodim was required for larger Texas panicum (>15 cm). Clethodim plus COC or MSO + AMS provided the greatest control of Texas panicum. This study demonstrated that successful Texas panicum management depends on applying clethodim at the optimum size and selecting the appropriate oil-based adjuvant especially at larger Texas panicum sizes.

Florpyrauxifen-benzyl is a postemergence rice herbicide that has reduced rice yield in some situations, and producers are concerned that the impact could be even greater with low rice seeding densities. Therefore, research was conducted in Stoneville, MS, from 2019 to 2021, to evaluate the effect of florpyrauxifen-benzyl on rice yield when a hybrid was seeded at reduced densities. Rice cultivar FullPage RT 7521 FP was seeded at 10, 17, 24, 30, and 37 kg ha−1. At the 4-leaf to 1-tiller growth stage, florpyrauxifen-benzyl was applied at 0 or 58 g ai ha−1. Rice injury following application of florpyrauxifen-benzyl was ≤8% across all seeding rates and evaluation intervals. Application of florpyrauxifen-benzyl reduced plant heights by 14% to all seeding rates but did not result in delayed rice maturity. When florpyrauxifen-benzyl was not applied to rice that was seeded at 10 and 17 kg ha−1 seeding rates, rice matured slower than when it was seeded at 24, 30, and 37 kg ha−1. When florpyrauxifen-benzyl was applied, rough rice grain yields were reduced by at the 17 and 37 kg ha−1 seeding rates, but not at any other seeding rate. In conclusion, application of florpyrauxifen-benzyl at a 2× rate can cause a loss of yield resulting from variation in rice densities.

In plasticulture production, smart-spray technology can detect weeds and apply herbicides only where needed in the area between raised, plastic-covered beds (row middle). This technology has the potential to reduce herbicide use and lower input costs. A prototype smart-spray system was developed at the Gulf Coast Research and Education Center in Wimauma, FL, that uses YOLO-V3 convolutional neural networks to differentiate broadleaf, grass, and nutsedge weeds in row middles. Two sets of field experiments were conducted to determine the efficacy of smart-spray technology using a combination of preemergence and postemergence herbicides. Weed density was reduced after all treatments, and targeted applications were as effective as banded treatments. Overall, including a preemergence herbicide tended to lower weed density compared to postemergence herbicides alone, regardless of application technique. Two banded preemergence herbicide applications and two targeted postemergence applications reduced herbicide use by 52% and 13% compared to banded preemergence and postemergence applications in Experiments 1 and 2, respectively. The reduction from two to one preemergence herbicide application did not result in an overall reduction in herbicide use or cost in Experiment 1 because the decrease in preemergence herbicides resulted in increased postemergence herbicide usage. In the absence of a banded preemergence application, with targeted postemergence applications compared to banded applications, herbicide usage was reduced by 40% to 67% in Experiment 1 and by 79% to 84% in Experiment 2. Smart-spray technology is an effective weed management tool for row middles in plasticulture production systems with or without preemergence-herbicide applications.

Introducing new herbicides requires a comprehensive understanding of how crops respond to various herbicide-related factors. Fluridone was registered for use in rice production in 2023, but research on rice tolerance to this herbicide is lacking. Hence, field research aimed to 1) evaluate the effect of fluridone application timing on rice tolerance and 2) assess rice response to fluridone in a mixture with standard rice herbicides applied to 3-leaf rice. Both experiments were conducted in a delay-flooded dry-seeded system using a randomized complete block design, with four replications. Treatments in the first experiment included a nontreated control and 10 application timings, ranging from 20 d preplant to postflood. The second experiment had a two-factor factorial structure, with factor A being the presence/absence of fluridone, and factor B being herbicide partners, including bispyribac-sodium, fenoxaprop, penoxsulam, propanil, quinclorac, quizalofop, and saflufenacil. In the first experiment, the maximum injury in 2022 was 28%, caused by the preemergence treatment. In 2023, fluridone applied preemergence caused the greatest injury (42%) 2 wk after flood establishment, declining to 37% in late season (13 d before rice reached 50% heading). Yield reductions of 21% occurred with the delayed preemergence treatment in 2022 and 42% with the preemergence treatment in 2023. Mixing fluridone with standard herbicides increased rice injury by no more than eight percentage points compared with the herbicides applied alone. Additionally, no adverse effects on rice groundcover or grain yield resulted from fluridone in the mixture. These results indicate a need to avoid fluridone applications near planting because of negative impacts on rice. Furthermore, fluridone can be mixed with commonly used rice herbicides, offering minimal risk to rice.

Commercial targeted sprayer systems allow producers to reduce herbicide inputs but risks the possibility of not treating emerging weeds. Currently, targeted applications with the John Deere system have five spray sensitivity settings, and no published literature discusses the effects of these settings on detecting and spraying weeds of varying species, sizes, and positions in crops. Research was conducted in Arkansas, Illinois, Indiana, Mississippi, and North Carolina on plantings of corn, cotton, and soybean to determine how various factors might influence the ability of targeted applications to treat weeds. These data included 21 weed species aggregated to six classes with height, width, and densities ranging from 25 to 0.25 cm, 25 to 0.25 cm, and 14.3 to 0.04 plants m−2, respectively. Crop and weed density did not influence the likelihood of treating the weeds. As expected, the sensitivity setting alters the ability to treat weeds. Targeted applications (across sensitivity settings, median weed height and width, and density of 2.4 plants m−2) resulted in a treatment success of 99.6% to 84.4% for Convolvulaceae, 99.1% to 68.8% for decumbent broadleaf weeds, 98.9% to 62.9% for Malvaceae, 99.1% to 70.3% for Poaceae, 98.0% to 48.3% for Amaranthaceae, and 98.5% to 55.8% for yellow nutsedge. Reducing the sensitivity setting reduced the ability to treat weeds. The size of weeds aided targeted application success, with larger weeds being more readily treated through easier detection. Based on these findings, various conditions can affect the outcome of targeted multinozzle applications. Additionally, the analyses highlight some of the parameters to consider when using these technologies.

Glufosinate serves as both a primary herbicide option and a complement to glyphosate and other postemergence herbicides for managing herbicide-resistant weed species. Enhancing broadleaf weed control with glufosinate through effective mixtures may mitigate further herbicide resistance evolution in soybean and other glufosinate-resistant cropping systems. Two field experiments were conducted in 2020 and 2021 at four locations in Wisconsin (Arlington, Brooklyn, Janesville, and Lancaster) and one in Illinois (Macomb) to evaluate the effects of postemergence-applied glufosinate mixed with inhibitors of protoporphyrinogen oxidase (PPO) (flumiclorac-pentyl, fluthiacet-methyl, fomesafen, and lactofen; Group 14 herbicides), bentazon (a Group 6 herbicide), and 2,4-D (a Group 4 herbicide) on waterhemp control, soybean phytotoxicity, and yield. The experiments were established in a randomized, complete block design with four replications. The first experiment focused on soybean phytotoxicity 14 d after treatment (DAT) and yield in the absence of weed competition. All treatments received a preemergence herbicide, with postemergence herbicide applications occurring between the V3 and V6 soybean growth stages, depending on the site-year. The second experiment evaluated the effect of herbicide treatments on waterhemp control 14 DAT and on soybean yield. Lactofen, applied alone or with glufosinate, produced the greatest phytotoxicity to soybean at 14 DAT, but this injury did not translate into yield loss. Mixing glufosinate with 2,4-D, bentazon, and PPO-inhibitor herbicides did not increase waterhemp control, nor did it affect soybean yield compared to when glufosinate was applied alone, but it may be an effective practice to reduce selection pressure for glufosinate-resistant waterhemp.

During the 2019 growing season, seeds of Palmer amaranth and common waterhemp were collected from 141 and 133 agricultural sites, respectively, from across the southeastern and midwestern United States. These accessions were screened with a new protoporphyrinogen oxidase (PPO) inhibitor, epyrifenacil, using a whole-plant bioassay at 20 g ai ha−1 in controlled environmental conditions to estimate its efficacy on these two agronomically important weeds. In addition, the coding sequence of the PPX2 gene was determined for plants from each accession through short-read sequencing of cDNA fragments amplified via polymerase chain reaction. Results showed that nearly all accessions were completely controlled by epyrifenacil, with average survival rates of less than 2% for both species. Target site resistance mutations toward PPO inhibitors were lower in Palmer amaranth (<20%) compared to waterhemp, with nearly half of all waterhemp samples (42%) possessing the ΔG210 allele, which is shown to cause high-level resistance to other commercially available PPO-inhibiting herbicides. Follow-up testing of accessions with high frequency (≥50%) of the ΔG210 allele of PPX2 compared the efficacy of epyrifenacil, saflufenacil, and saflufenacil + trifludimoxazin and showed that of the herbicides tested, epyrifenacil at 20 g ha−1 provided the best control, averaging 85% mortality across these accessions. Same-plant association study of molecular data and whole-plant assay correlated all detected variants of PPX2 with visual injury following epyrifenacil treatment and found that the ΔG210 mutation was associated with a reduction in relative efficacy of epyrifenacil in some accessions. All other known target site resistance mutations appeared to have no significant effect on epyrifenacil efficacy.

Smooth scouringrush is an herbaceous perennial with an extensive underground rhizome system that has invaded no-till dryland production fields in the inland Pacific Northwest. The objective of this field study was to determine whether there were any short- or long-term benefits to tank-mixing chlorsulfuron + metsulfuron with glyphosate for smooth scouringrush control. Field studies were conducted at three sites across eastern Washington from 2020 to 2024. Glyphosate was applied during fallow periods at 0, 1,260, 2,520, and 3,780 g ae ha−1 with and without chlorsulfuron + metsulfuron applied at 21.9 + 4.4 g ai ha−1. Smooth scouringrush stem density was evaluated 1, 2, and 3 yr after treatment. Chlorsulfuron + metsulfuron provided excellent control of smooth scouringrush (<5 plants m−2) for the first 2 yr at all three sites, and there was no observed benefit of tank-mixing with glyphosate. This continued to be the case 3 yr after treatment at two of the sites, but at one site, adding glyphosate at 2,520 or 3,780 g ha−1 to chlorsulfuron + metsulfuron decreased stem density compared to chlorsulfuron + metsulfuron applied alone. For treatments containing glyphosate only, the greatest efficacy 3 yr after treatment was achieved at the highest application rate of 3,780 g ha−1. Although no short-term benefit was observed in adding glyphosate to chlorsulfuron + metsulfuron for smooth scouringrush control, at one of three sites the duration of control was increased by at least 1 yr with the addition of glyphosate at a rate of 2,520 g ha−1 or more and an organosilicone surfactant as tank-mix partners.

This study evaluated the impact of four cover crop species and their termination timings on cover crop biomass, weed control, and corn yield. A field experiment was arranged in a split-plot design in which cover crop species (wheat, cereal rye, hairy vetch, and rapeseed) were the main plot factor, and termination timings [4, 2, 1, and 0 wk before planting corn (WBP)] was the subplot factor. In both years (2021 and 2022), hairy vetch produced the most biomass (5,021 kg ha–1) among cover crop species, followed by cereal rye (4,387 kg ha–1), wheat (3,876 kg ha–1), and rapeseed (2,575 kg ha–1). Regression analysis of cover crop biomass with accumulated growing degree days (AGDDs) indicated that for every 100 AGDD increase, the biomass of cereal rye, wheat, hairy vetch, and rapeseed increased by 880, 670, 780, and 620 kg ha–1, respectively. The density of grass and small-seeded broadleaf (SSB) weeds at 4 wk after preemergence herbicide (WAPR) application varied significantly across termination timings. The grass and SSB weed densities were 56% and 36% less at 0 WBP compared with 2 WBP, and 67% and 61% less compared with 4 WBP. The sole use of a roller-crimper did not affect the termination of rapeseed at 0 WBP and resulted in the least corn yield (3,046 kg ha–1), whereas several different combinations of cover crops and termination timings resulted in greater corn yield. In conclusion, allowing cover crops to grow longer in the spring offers more biomass for weed suppression and impacts corn yield.

Herbicide-resistant weeds demand particular attention in the selection of management strategies, considering the characteristics and fitness differences between susceptible and resistant plants. This study aimed to analyze two heterogeneous junglerice populations, glyphosate-susceptible (EC-S) and glyphosate-resistant (EC-R), derived from field-collected seeds, to quantify the productivity of EC-S and EC-R, to analyze the impact of soybean plants, and to evaluate density dependence. Experiments were conducted in a growth chamber using plastic pots, combining three factors: junglerice density (2, 4, and 8 plants pot−1), the proportion of EC-S and EC-R (100% EC-S, 50% EC-S:50% EC-R, 100% EC-R), and soybean density (0 and 1 plants pot−1). One-leaf junglerice seedling and soybean seeds were planted in plastic pots. After 65 d, plant height (PLH), total number of tillers (TIL), seed number (SEN), seed weight (SEW) per plant, weight of 100 seeds (HSW), and aboveground dry matter (ADM) were measured. The variables measured were affected primarily by junglerice density and the presence of soybean. Vegetative and reproductive structures of EC-S and EC-R exhibited strongly density-dependent patterns. One soybean plant increased (P < 0.05) junglerice productivity at low densities but had no effect at high densities (8 plants pot−1). Mostly EC-S and EC-R showed the same competitive ability. However, EC-S presented a higher index of competitive ability than EC-R in SEN and SEW at lower densities with a soybean plant. A resource complementarity (RYT ∼ 1) between EC-S and EC-R was observed (P < 0.05), regardless of the presence of the crop. These results demonstrate that, even in the absence of glyphosate, fitness differences favor heterogeneous resistant populations. This highlights the inherent adaptive advantage of resistant populations and, considering the extensive reliance on glyphosate in current production systems, underscores the urgent need for integrated weed management strategies to mitigate the evolution and spread of resistant populations.

Liverwort (Marchantia polymorpha L.) is a problematic weed for nurseries and greenhouses, and currently, no effective method exists for controlling it in greenhouses. This study assessed liverwort growth, reproduction, and its competitiveness with ornamental plants in response to the strategic placement of controlled-release fertilizers (CRFs). CRFs were top dressed, incorporated, subdressed, and dibbled on liverwort growth and reproduction. CRFs were subdressed or dibbled at depths of 2.5, 5.1, or 7.6 cm. In each container, the top of the growing medium was inoculated with liverwort gemmae, and the percentage of the container surface covered by liverwort thalli was visually estimated after 2, 4, 6, 8, 10, and 12 wk. At 12wk, gemma cups were counted and after 28 wk, the number of sexual reproductive structures (antheridiophores and archegoniophores) and total fresh biomass of liverwort were recorded. Liverwort growth, gemmae formation, and number of archegoniophores were lowest when CRFs were dibbled or subdressed at depths of 7.6 cm. We also investigated the effects of CRF placement on liverwort competitiveness with a dicot wax begonia (Begonia semperflorens-cultorum L.) and a monocot dracaena (Cordyline indivisa L.). One week after planting the ornamentals and gemmae application, liverwort was thinned to contain 0, 3, or 9 gemmalings per container. The percent increase in growth index of the ornamental plants, and the fresh mass of liverwort and ornamental plants were recorded at the end of the experiment. Results indicated that CRF subdressing and dibbling applied at 7.6 cm were the most effective in reducing liverwort coverage and biomass while improving the growth of both begonia and dracaena. The highest liverwort coverage was measured in containers in which CRF was incorporated. Therefore, strategic fertilizer placement can be an effective method of managing liverwort growth in ornamental container production both in terms of the quality of the ornamentals and their competitiveness with liverwort.

Geyer larkspur is a native perennial forb that is toxic to cattle. Herbicide control of Geyer larkspur is variable and depends on the growth stage of the plant when the herbicide is applied. The objectives of this study were to 1) evaluate aminopyralid, aminopyralid + florpyrauxifen-benzyl, aminopyralid + 2,4-D, aminopyralid + metsulfuron-methyl, metsulfuron-methyl, triclopyr, and triclopyr + 2,4-D for efficacy in controlling Geyer larkspur; 2) determine whether plant growth stage (vegetative or flowering) at the time of herbicide application influences herbicide effectiveness; and 3) determine whether herbicide treatment alters the norditerpenoid alkaloid content of Geyer larkspur. Plots were established in eastern Wyoming in 2021 and northern Colorado in 2022. Herbicide application at the different phenological stages did not affect Geyer larkspur density at the Wyoming site (P = 0.1065; data not shown). Geyer larkspur density at the Wyoming site was reduced by all herbicide treatments 1 yr after treatment (YAT) at the vegetative stage and by all herbicides except triclopyr 2 YAT (P = 0.0249). Geyer larkspur density at the flowering stage was reduced by all herbicides except metsulfuron-methyl, triclopyr, and triclopyr + 2,4-D at 1 YAT and by triclopyr and triclopyr + 2,4-D at 2 YAT. In contrast, there were no differences in Geyer larkspur density across treatments at the Colorado site (P = 0.9621). Precipitation was below average several months prior to herbicide application, which may have affected herbicide effectiveness. The metsulfuron-methyl treatment resulted in the highest total alkaloid concentrations of Geyer larkspur at the vegetative stage and the lowest concentrations at the flowering stage at the Wyoming site. Efforts to control Geyer larkspur in semiarid rangelands can be effectively accomplished by applying aminopyralid herbicides at either the vegetative or flowering growth stage provided environmental conditions prior to herbicide application are sufficient for plant growth and uptake of the herbicide.

Enlist E3® soybean is resistant to 2,4-D, glyphosate, and glufosinate, allowing postemergence applications of these herbicides sequentially or as tank mixes. The objectives of this experiment were to evaluate the effect of postemergence herbicide application timing and sequence with or without a preemergence application of micro-encapsulated acetochlor on waterhemp and common lambsquarters control, soybean yield, and economic returns. Field experiments were conducted in Rosemount and Franklin, Minnesota, in 2021 and 2022. Site, herbicide application timing, and sequence influenced weed control, yield, and profitability. In Rosemount, preemergence followed by (fb) two-pass postemergence programs, including 2,4-D + glyphosate applied at mid-postemergence with or without S-metolachlor, resulted in ≥95% waterhemp control at 28 d after late postemergence application. In Franklin, where weed density was lower, two-pass postemergence programs, regardless of preemergence application that included at least one application of 2,4-D + glyphosate (with or without S-metolachlor), provided ≥97% control of waterhemp and common lambsquarters at 28 d after late postemergence. The level of control was comparable to that of a preemergence herbicide fb a mid-postemergence application of 2,4-D + glyphosate + S-metolachlor at that site. In Rosemount, including acetochlor as the preemergence herbicide in the preemergence fb postemergence programs improved soybean yield by 32% and partial returns by US$384.50 ha−1 compared to postemergence herbicides–only programs. In contrast, the preemergence application did not affect yield or profitability in Franklin. The highest soybean yield (2,925.7 kg ha−1) in Rosemount resulted after glufosinate was applied early postemergence fb 2,4-D + glyphosate applied mid-postemergence. This yield was comparable to that of glufosinate applied early postemergence fb 2,4-D + glyphosate + S-metolachlor applied mid-postemergence and the two-pass glufosinate (early postemergence fb mid-postemergence) program, highlighting the importance of early season weed control. In Franklin, 2,4-D + glyphosate + S-metolachlor (applied mid-postemergence) fb glufosinate (applied late postemergence) provided a yield that was similar to the aforementioned programs at that site.