Several Elaeagnus species (autumn olive [E. umbellata (Thunb.)], Russian olive [E. angustifolia (L.)], and thorny olive [E. pungens (Thunb.)]) are invasive in North America. Elaeagnus pungens is prevalent throughout much of the southeastern United States, commonly overtaking wooded and natural areas, bottomlands, and roadsides. While many management methods including several herbicide treatments have been evaluated, efficacy of these methods can vary based on the size and density of the target plants. Further, personal communication with land managers revealed a lack of information that incorporated application effort, duration and associated cost into treatment efficacy and usefulness. We evaluated three herbicide application methods using the free acid formulation of triclopyr in an E. pungens infested forest in South Carolina, United States to determine the effectiveness of each application method. We estimated pre-treatment E. pungens biomass and destructively harvested all live material post treatment to obtain actual biomass values. Foliar herbicide application was ineffective, but both cut stump and basal bark application nearly eliminated E. pungens in the treatment plots. The basal bark application took slightly more time to complete than cut stump treatments but was described as less physically demanding by applicators. Based on treatment efficacy and time required, the basal bark application method seems most prudent for controlling E. pungens in these areas. These results will help land managers more effectively use their resources for invasive woody plant control.

We evaluated herbicides for controlling the annual grass ventenata [Ventenata dubia (Leers) Coss.], with particular interest in indaziflam, a preemergence cellulose biosynthesis inhibitor. In 2016, indaziflam was applied postemergence alone and in mixture with glyphosate, imazapic, propoxycarbazone-sodium, or rimsulfuron to an improved pasture in southwestern Montana. A non-sprayed control was included for comparison purposes. Canopy cover of each species was assessed annually for 7 yr; cover was grouped by life-form and longevity, and species richness was calculated. Five years (2021) after treatment, the seedbank was assessed. Our results indicated that treatments including indaziflam reduced V. dubia cover 1 to 3 yr and even up to 6 yr after application, with V. dubia cover being zero or close to zero. However, at 7 yr (2023) after treatment, V. dubia was low across all treatments, including the non-sprayed control. Perennial grasses and forbs and annual forbs were generally unaffected by any treatment and did not increase in cover over the 7 yr, even though V. dubia decreased. Two years after treatment, species richness was lowest in treatments that included indaziflam, but at 7 yr, species richness was similar across all treatments. Indaziflam depleted the monocot and dicot seedbank, with fewer than 5 seedlings of any species emerging from treatments that included indaziflam, while other treatments resulted in 60 to 165 seedlings per sample (40 cm3 of soil). In summary, at our study site, a single application of indaziflam controlled V. dubia for 6 yr, appeared to deplete the seedbank at 5 yr, and cover of perennial and annual vegetation and species richness was unaffected. By the end of the study, though, V. dubia cover appeared to be influenced by factors other than herbicide treatments, possibly variable precipitation over time, an exclusion of grazing, and competitive perennial grasses dominating the site.

Tetflupyrolimet (Dodhylex™ Active, FMC Corporation) is a novel herbicide inhibiting de novo pyrimidine biosynthesis that controls grassy weeds preemergence in rice (Oryza sativa L.) production. Field trials were conducted from 2021 to 2024 to evaluate turfgrass tolerance to tetflupyrolimet applications for annual bluegrass (Poa annua L.) and smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] control. Tolerance was evaluated on seven turfgrass species, including creeping bentgrass (Agrostis stolonifera L.), Kentucky bluegrass (Poa pratensis L.), tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.; syn.: Festuca arundinacea Schreb.], hybrid bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy], and manilagrass [Zoysia matrella (L.) Merr.] at various mowing heights ranging from 3.8 to 12.5 mm. Separate experiments were conducted on each turfgrass species to evaluate tolerance in both fall and spring. Tetflupyrolimet was applied at rates of 0, 25, 50, 100, 200, 400, 800, 1600, 3200, or 6400 g ai ha−1. No injury was observed on any warm-season turfgrass species in either season, whereas cool-season grass tolerance varied among species each season; however, cool-season turfgrass tolerance for all species was greater in spring than fall. While efficacy of tetflupyrolimet (400 g ha−1) for preemergence D. ischaemum control varied among years, mixtures of tetflupyrolimet (400 g ha−1), pyroxasulfone (128 g ai ha−1), and rimsulfuron (35 g ai ha−1) applied preemergence or early postemergence effectively controlled multiple-resistant P. annua in both seasons. Overall, these findings highlight that warm-season turfgrasses are highly tolerant of tetflupyrolimet applications for P. annua or D. ischaemum control.

This study assessed the potential of using dichlobenil to manage hair fescue in lowbush blueberry crops when targeted or broadcast-applied (7,000 g ai ha−1) as justification for developing a precision-targeted applicator. A randomized complete block design was used to assess both application methods, and results were compared with industry-standard propanamide (2,240 g ai ha−1). Targeted and broadcast-applied dichlobenil in fall 2020 significantly reduced average total tuft density in the nonbearing year (2021) by 75% and 67%, respectively, and in the bearing year (2022) by 61% and 59%, respectively. Broadcast pronamide applications in fall 2020 significantly reduced total tuft density by 84% in the nonbearing year (2021) and 81% in the bearing year (2022). These reductions in total tuft density resulted in average lowbush blueberry yields of 416, 557, 573, and 617 g m−2 for the control, pronamide applications, and targeted and broadcast-applied dichlobenil, respectively. Increases in yield were not significant, though the large variation within the sample is the probable cause. The similarities between targeted and broadcast-applied treatments demonstrate the potential of using targeted dichlobenil. Given the high product cost of dichlobenil at Can$1,873 ha−1, hair fescue’s non-uniform distribution in lowbush blueberry fields and the lowbush blueberry industry’s overreliance on pronamide, targeted application of dichlobenil has significant potential. This work justifies the development of a mechanized precision-targeted applicator for use in lowbush blueberry cropping systems.

Italian ryegrass control is one of the most significant limitations in wheat production in the United States today. Resistance to Herbicide Resistance Action Committee (HRAC)/Weed Science Society of America (WSSA) Groups 1, 2, and 9 in Arkansas have further complicated postemergence control, whereas residual herbicides still show effective weed control. One problem is the potential of HRAC/WSSA Group 15 herbicides to injure wheat when applied preemergence, indicating the need for a herbicide safener. A series of experiments were conducted in Fayetteville, AR, to evaluate crop tolerance and Italian ryegrass control using a capsule suspension (CS) formulation of S-metolachlor in conjunction with fenclorim-treated wheat. Experiments were conducted as a two-factor factorial with S-metolachlor applied at three rates (0.37, 0.74, and 1.12 kg ai ha–1) and a microencapsulated formulation of acetochlor at 1.05 kg ai ha–1, and three rates of a fenclorim seed treatment at 0, 0.5, and 2.0 g ai kg–1 of seed. Separate experiments utilized either a preemergence (PRE) or a delayed-preemergence (DPRE) application timing. In both experiments, S-metolachlor at 0.74 and 1.12 kg ai ha–1 provided 77% to 96% control of Italian ryegrass by preharvest, whereas acetochlor only provided 49% to 72% control. Visible wheat injury from PRE applications ranged from 7% to 49% for all treatments 21 d after treatment (DAT), with a reduction in injury when fenclorim-treated wheat was used for both the 0.74 and 1.12 kg ai ha–1 rate of S-metolachlor. In the DPRE experiments, wheat injury ranged from 5% to 16% 21 DAT with no noticeable safening from the presence of fenclorim at any herbicide rate. The results of these experiments indicate that a DPRE application using a CS formulation of S-metolachlor would be more favorable for producers to mitigate the potential for injury to wheat while providing Italian ryegrass control. Additionally, at the DPRE application timing, fenclorim is unnecessary for S-metolachlor to be safely applied at the rates evaluated.

Commercialization of florpyrauxifen-benzyl as Loyant® in 2018 as a synthetic auxin herbicide in rice was followed by soybean injury due to off-target movement of spray applications in the mid-southern United States. Concerns surrounding off-target movement led to the exploration of an alternative application method to help alleviate the issue. Field experiments were conducted in 2020 and 2021 to explore the likelihood of a reduction in soybean injury following applications of florpyrauxifen-benzyl coated on urea in narrow- and wide-row soybean systems and to determine the likelihood of volatilization from this novel application method. Florpyrauxifen-benzyl spray-applied at 0.18 g ai ha−1 caused greater than 60% injury, whereas coating the herbicide on urea at 5.63 g ai ha−1 never exceeded 30% injury in narrow-row soybean. Similarly, florpyrauxifen-benzyl spray-applied at 0.18 g ai ha−1 caused greater than 50% injury, whereas coating the herbicide on urea at 5.63 g ai ha−1 never exceeded 30% injury in wide-row soybean. As soybean injury increased, relative yield decreased in both narrow- and wide-row soybean. Spray-applied florpyrauxifen-benzyl decreased relative soybean groundcover, yield components, and soybean survival rate as the herbicide rate increased, whereas coating the herbicide on urea resulted in little to no decrease in both narrow- and wide-row soybean assessments. No negative impacts on relative yield and yield components of soybean from florpyrauxifen-benzyl coated on urea indicates that even though visible injury may persist, there is a low likelihood of any yield losses associated with the herbicide exposure using this application method. Additionally, coating the florpyrauxifen-benzyl on urea did not increase the likelihood of volatilization under any of the evaluated soil moisture conditions. Overall, applying florpyrauxifen-benzyl coated on urea is likely to be a safer application method and can reduce soybean injury compared to spray-applying the herbicide when favorable off-target movement conditions exist.

Yellow and knotroot foxtail are two common weed species infesting turfgrass and pastures in the southeastern region of the United States. Yellow and knotroot foxtail share morphological similarities and are frequently misidentified by weed managers, thus leading to confusion in herbicide selection. Greenhouse research was conducted to evaluate the response of yellow and knotroot foxtail to several turfgrass herbicides: pinoxaden (35 and 70 g ai ha−1), sethoxydim (316 and 520 g ai ha−1), thiencarbazone + dicamba + iodosulfuron (230 g ai ha−1), nicosulfuron + rimsulfuron (562.8 g ai ha−1), metribuzin (395 g ha−1), sulfentrazone (330 g ai ha−1), sulfentrazone + imazethapyr (504 g ai ha−1), and imazaquin (550 g ai ha−1). All treatments controlled yellow foxtail >87% with more than 90% reduction of the biomass. By comparison, only sulfentrazone alone controlled knotroot foxtail 90% and completely reduced aboveground biomass. Sethoxydim (520 g ai ha−1), metribuzin, and imazaquin controlled knotroot foxtail >70% at 28 d after application. In a rate response evaluation, nonlinear regression showed that yellow foxtail was approximately 8 times more susceptible to pinoxaden and 2 times more susceptible to sethoxydim than knotroot foxtail based on log (WR50) values, which were 50% reduction in fresh weight. Our research indicates that knotroot foxtail is more difficult to control across a range of herbicides, making differentiation of these two species important before herbicides are applied.

Native aquatic macrophytes such as American eelgrass (Vallisneria americana Michx.) are often desirable in aquatic ecosystems due to the ecological benefits they provide but are threatened by competition from invasive taxa including non-native Vallisneria taxa and hydrilla [Hydrilla verticillata (L. f.) Royle]. Identifying potential selective herbicide management options can provide tools to minimize impacts to native taxa in restoration and aquatic invasive plant management programs. Greenhouse mesocosm experiments were conducted in 2023 to investigate herbicide efficacy on two native eelgrass species (V. americana and Vallisneria neotropicalis Vict.), two non-native taxa (Vallisneria australis S.W.L. Jacobs & Les and Vallisneria spiralis L. × Vallisneria denseserrulata Makino), and H. verticillata. Herbicide applications included endothall, diquat, florpyrauxifen-benzyl, fluridone, and flumioxazin and select combinations of these herbicides used in H. verticillata management. Endothall alone provided 90% to 100% aboveground biomass reduction at 3,000 µg L−1 with at least 24 h of continuous or intermittent exposure to all native and invasive species at 6 wk after exposure, whereas florpyrauxifen-benzyl applied alone resulted in minimal aboveground biomass reduction. A 45-d of exposure of fluridone (10 µg L−1) resulted in 95% biomass reduction of V. americana and 7% to 48% of other tested taxa. The combination of flumioxazin and florpyrauxifen-benzyl resulted in 90% to 100% aboveground biomass reduction, and endothall combined with florpyrauxifen-benzyl resulted in 93% to 100% aboveground biomass reduction across taxa. Reductions in belowground biomass mirrored trends observed in aboveground biomass. No treatments selectively controlled invasive Vallisneria without injury to native Vallisneria, although efficacy was observed on H. verticillata. These insights provide an understanding for differences between these Vallisneria for researchers moving forward with selectively targeting H. verticillata in the presence of native Vallisneria species and two new aquatic invasive plants. Future research should expand treatment scenarios, increase the study period, and identify potential integrated plant management strategies for field scenarios.

Adsorption studies indicate that paraquat, diquat, and thionine are bound on bentonite by amounts greater than the measured cation-exchange capacity (CEC) of the clay. Methylene blue, new methylene blue, and malachite green are bound by amounts equal to the CEC. The unipositive organocations form aggregates on the clay surface. Aggregation increases with ionic strength and increases the apparent adsorption capacity by 25%. The aggregates are removed by washing with distilled water. Desorption studies show that the dyes are irreversibly bound, whereas the dipositive organocations are reversibly bound. Ionic strength variation reduces adsorption by 15 and 36% in the monovalent and divalent organocation-clay systems, respectively. In the clay-divalent organocation systems adsorption is greater on Na-saturated clay than on K-saturated clay. Adsorption is unchanged over the pH range 4.5–8.5 and decreases steadily below pH 4.0. Changes in adsorption due to changes in temperature are small. The study indicates that ionic strength is the most important variable in clay-organocation interactions.

The adsorption mechanism of iso-propylammonium (PAH+), the cationic component of Roundup, by various homoionic montmorillonites and the structures of the associations obtained in the interlayer space were investigated, using infrared, X-ray, and carbon analysis methods. Adsorption from aqueous and ethanol solutions of Roundup was studied. The infrared spectra were compared with those obtained by the treatment of montmorillonites with ethanol and CCl4 solutions of the free iso-propylamine (PA). The adsorption of PA from ethanol gives rise to protonation of the amine. PA sorbed from CCl4 solution forms an ammonium-amine association. Adsorption of PAH+ from alcohol solution of Roundup occurs by the mechanism of cation exchange. With transition metal exchangeable cations, PAH+ is sorbed in excess, forming hydrogen bonds between NH3+ groups and hydroxyls resulting from dissociation of water molecules. The process of adsorption of PAH+ from aqueous solutions of Roundup depends on the concentration of the solution. If montmorillonite is reacted with 0.5% solution of Roundup, PAH+ is adsorbed by exchanging metal cations and the adsorption capacity of the clay does not exceed the c.e.c. If the montmorillonite is reacted with 5.0% solution of Roundup, the PAH+ exchanges protons originating from the hydrolysis of the interlayer water. Protons which are transferred from the interlayer space to the water solution are accepted by the anion component of Roundup. The amounts of PAH+ adsorbed from concentrated Roundup solutions are much higher than the cation exchange capacity of montmorillonite. Hydrogen bonds are formed between the ammonium and water or hydroxyl groups on the interlayer space. With the trivalent exchange ions Al and Fe, which tend to polymerize in the interlayer space, excess sorption gives rise to hydrogen bonding of NH3+ to oxygen of the polymer.

The reaction between the herbicide “Roundup,” (PAH)3G, which is the commercial name of the iso-propylammonium salt of glyphosate (H3G, N-phosphonomethyl glycine), and montmorillonite was studied. The adsorption of the anionic component of Roundup glyphosate anion, G−3, from an ethanol solution is achieved by repeated immersion of the clay film in the alcohol solution followed by drying for 6–12 hr after each immersion. During the adsorption process the surface acidity of the interlayer space must be sufficiently high to protonate the anion. A zwitterion glyphosate is thereby formed in the interlayer space. Association forms are obtained in the interlayer space in which the COOH and the PO3H groups are linked to the exchangeable cations through water bridges. Adsorption of the glyphosate anion from aqueous solution of Roundup occurs when this anion forms a neutrally or positively charged complex with the exchangeable cation. This may occur with Al- and Fe-montmorillonite, when the molar ratio glyphosate:metal is such that a complex with a 1:1 ratio can be formed in the interlayer space. To clarify the reaction mechanism, adsorption of glycine by montmorillonite from ethanol solution was also studied. The associations obtained between glyphosate and exchangeable cations are less variable than those obtained between glycine and exchangeable cations in the interlayer space of montmorillonite. The following species of adsorbed glycine were identified: glycinium cation, zwitterion glycine, glycine complexed with metal cations either as a monodentate or as a bidentate ligand. In the latter case a chelate is formed.

Off-target movement of growth regulator herbicides can cause severe injury to susceptible plants. Apart from not spraying on windy days or at excessive boom heights, making herbicide applications using nozzles that produce large droplets is the preferred method for reducing herbicide drift. Although large droplets maintain a higher velocity and are more likely to reach the leaf surface in windy conditions, their ability to remain on the leaf surface is poorly understood. Upon impact with the leaf surface, droplets may shatter, bounce, roll off, or be retained on the leaf surface. We examined how different nozzles, pressures, and adjuvants impact spray droplet adsorption on the leaf surface of common lambsquarters and soybean. Plants were grown in a greenhouse and sprayed in a spray chamber. Three nozzles (XR, AIXR, and TTI) were evaluated at 138, 259, and 379 kPa, respectively. Dicamba (0.14 kg ae ha−1) was applied alone and with methylated seed oil (MSO), a non-ionic surfactant, silicone-based adjuvant, crop oil concentrate, or a drift reduction adjuvant. A 1,3,6,8-pyrene tetra sulfonic acid tetra sodium salt was added as a tracer. Dicamba spray droplet adsorption when using the XR nozzle, which produced the smallest spray droplets, was 1.75 times greater than when applied with the TTI nozzle with the largest spray droplets. Applying dicamba with MSO increased adsorption on leaf surfaces nearly 4 times the amount achieved without an adjuvant. The lowest application pressure (138 kPa) increased dicamba spray volume adsorbed more than 10% compared to the higher pressures of 259 and 379 kPa. By understanding the impacts of these application parameters on dicamba spray droplet adsorption, applicators can select application parameters, equipment, and adjuvants that will maximize the amount of dicamba spray volume retained on the target leaf surface while minimizing dicamba spray drift.

Two separate field studies were conducted at two locations near Crowley, Louisiana, to evaluate early season applications of florpyrauxifen and a prepackaged mixture of halosulfuron plus prosulfuron in water-seeded rice production. In each study, florpyrauxifen and halosulfuron plus prosulfuron were applied at two rates and either applied to the soil surface 48 h before the seeding flooding and seeding, directly onto the pregerminated seed 24 h following seeding and immediately after removal of the seeding flood (SEED), and at pegging. Data suggest that both florpyrauxifen and halosulfuron plus prosulfuron have a role to play in water-seeded rice production. Crop injury of 19% was observed from applications of florpyrauxifen applied directly to pregerminated SEED. Additionally, 28% crop injury was observed when halosulfuron plus prosulfuron was applied directly to SEED. Due to crop injury observations, both herbicides should be avoided when the pregerminated seed is exposed to the soil surface after removing the seeding flood. These data suggest that florpyrauxifen may be a better option for postemergence application, whereas halosulfuron plus prosulfuron may be a better preemergence option in water-seeded rice production. Overall, the findings show that both herbicide technologies will provide adequate early-season weed control in water-seeded rice production.

In Oklahoma, downy brome and cheat are difficult-to-control winter annual grasses. In the past, cheat infested most of the winter wheat hectares harvested in Oklahoma. Biotypes that are cross-resistant to acetolactate synthase–inhibiting herbicides have left growers with minimal management options for conventional and herbicide-tolerant systems. Field trials near Lahoma, Oklahoma, in 2019–2020 and 2020–2021 evaluated integrated management of cheat and downy brome using three strategies: planting date (optimal, delayed, and late), cultivar selection (high and low competitiveness), and herbicide choice (no herbicide, sulfosulfuron at 35.2 g ai ha−1 and pyroxsulam at 18.4 g ai ha−1). Visual control, weed species present, wheat biomass at heading, and grain yield data were collected. In 2019–2020, 8 to 9 wk after treatment, visual control increased by 15% with the delayed planting compared with the optimal planting date and 14% with the late planting date. In 2020–2021, similar control (∼99%) was recorded for delayed and late plantings with 23% greater control than the optimal timing. Due to a lack of weed coverage, weed biomass in 2019–2020 had no response to planting date, cultivar, or herbicide treatment. Downy brome biomass during 2020–2021 was approximately 90% lower with delayed to late planting dates than the optimal planting date. In the same year, downy brome and cheat biomass were low (≤0.4 and 0.2 g m−2) and 98% less after an herbicide application than a nontreated area. Wheat grain yield at the optimal planting date was greater than yields from delayed and late plantings in 2019–2020. A delay in planting from the optimal date to delayed or late timings decreased wheat yield by 14% and 21%, respectively. In 2020–2021, wheat yield from the late planting was reduced by 57% compared with the optimal planting yield. Delaying the planting date and the use of a common herbicide can suppress cheat and downy brome, but a decline in wheat yield may occur.

The adsorption and degradation on montmorillonite of s-triazine, the parent compound of a major group of triazine-based herbicides, were studied by Fourier-transform infrared spectroscopy. The original s-triazine appeared to hydrolyze with residual bound water in montmorillonite at 20°C to produce formamide, which formed an intercalate with the clay. A mechanism for the conversion of s-triazine to formamide was proposed which does not support earlier reports that formic acid and ammonia are the reaction products. The infrared spectrum of the formamide-Na-montmorillonite intercalate suggests that formamide reacted with the exchangeable Na cation and that the NH2 group hydrogen bonded with the clay. Assuming the intercalated formamide molecule to be planar, the molecular plane was found to be inclined at ~33° with respect to the plane of the silicate sheet. C-N and C-O bonds were also found to be tilted at the same angle with respect to the clay surface. The proposed orientation is in good agreement with the measured value of d(001) for the formamide-Na-montmorillonite complex. The proposed model of the formamide-montmorillonite complex serves as a basis for comparison of other clay-amide complexes that are important in protein-clay interactions.

Adsorption and catalytic decomposition of 4-nitrobenzenesulphonylmethylcarbamate (herbicide Nisulam) on Upton, Wyoming, bentonite saturated with different cations was studied using thin-layer chromatography and infrared spectroscopy. Nisulam is adsorbed at room temperature by coordination through the NO2 group to the exchange cation regardless of the cation's nature. On moderate heating (75°–90°C) this molecule decomposes to 4-nitrobenzenesulphonamide whereas a similar compound (herbicide Asulam) containing the NH2 functional group instead of NO2 is adsorbed by protonation at room temperature and decomposes into different products. For cations having a high polarizing power, a coordination bond between the Asulam molecule's C=O group and the exchange cation is established, and the molecule decomposes to sulphanilic and carbamic acid. In contrast, for cations having a low polarizing power there is no coordination, and the molecule decomposes mainly into sulphanilamide. Nisulam's coordination to the exchange cation through the NO2 group instead of C=O is ascribed to inductive and conjugation effects, typical of the nitro group.

Monitoring herbicide-resistant weeds makes it possible to study the evolution and spread of resistance, which provides important information for their management. The objective of this study was to map fleabane accessions in the states of Paraná (PR) and Mato Grosso do Sul (MS), Brazil, to identify herbicide-resistant accessions and their response to soybean preplant chemical burndown management strategies. Fleabane seeds were collected in agricultural areas in PR and MS in 2018, 2019, and 2020. Initial screening was performed for glyphosate, chlorimuron, paraquat, 2,4-D, saflufenacil, and glufosinate efficacy. Subsequently, dose-response experiments were conducted. Field experiments were carried out in three locations, where accessions of multiple herbicide–resistant Sumatran fleabane were identified. Herbicides were used in single or sequential applications at three plant heights (<5 cm, 5 to 10 cm, and >10 cm). After preliminary screening, accessions were classified as putative resistant (<80% control for all four replicates), segregated (<80% control for one to three replicates), or susceptible (>80% control for all four replicates). There was no evidence of resistance to glufosinate or saflufenacil in any of the 461 accessions, while 65 demonstrated possible resistance or segregation to glyphosate only, 235 to glyphosate + chlorimuron, 79 to glyphosate + chlorimuron + paraquat, 59 to glyphosate + chlorimuron + 2,4-D, and 23 with four-way resistance (glyphosate, chlorimuron, paraquat, and 2,4-D). Of these 23 accessions, seven were analyzed using dose-response curves (F2 generation), all from PR, confirming four-way resistance to glyphosate, chlorimuron, paraquat, and 2,4-D. To control resistant Sumatran fleabane, an application should prioritize smaller plants. Despite resistance to 2,4-D, double mixtures containing this herbicide were among the most effective treatments in plants <5 cm in height. If a sequential application is needed for plants >5 cm in height, we recommend glyphosate + synthetic auxin followed by glufosinate or glyphosate + saflufenacil.

The prolific seed production and polyploidy of annual bluegrass allow for the rapid development of herbicide resistance. Ethofumesate-resistant annual bluegrass plants were identified in the 1990s in grass seed production in Oregon, but their prevalence and distribution are not well documented. Therefore a dose–response experiment was initiated to determine the potential level of ethofumesate resistance in seed production systems. Seeds from 55 annual bluegrass populations were obtained from three sources: seed production fields (31 populations), the seed cleaning process (6 populations), and seed testing lots prior to retail distribution (18 populations). Additionally, two populations, one with known ethofumesate resistance and one with known susceptibility, were identified in preliminary testing and used as controls in this experiment. Seed from each collected population was increased. Individual seedlings were then transplanted into separate cone-tainers, grown to a size of 2 to 3 tillers in the greenhouse, and then sprayed using a compressed air track spray chamber with 10 doses of ethofumesate at 0, 0.56, 1.1, 2.8, 5.6, 8.4, 11.2, 16.8, 22.4, and 44.8 kg ai ha−1, with 0.84 to 2.2 kg ha−1 as the label application rate for perennial ryegrass. The resistant to susceptible ratio of populations across all sources ranged from 0.5 to 5.5. The most resistant populations found in production fields, seed cleaning, and seed testing lots had the effective dose necessary to kill 50% of the population (ED50) of 12.1, 9.4, and 13.1 kg ha−1, respectively. Furthermore, 68% of the populations found in production fields had ED50 higher than 6 kg ha−1, indicating common annual bluegrass resistance in grass seed production. As such, growers should implement integrated weed management strategies, as herbicides alone will likely be ineffective at controlling annual bluegrass.

Few herbicides are registered for goosegrass control in creeping bentgrass turfgrass. Topramezone controls goosegrass and is labeled for use on creeping bentgrass, but potential injury risks lead many turf managers to frequently apply it at a low-dose. This application practice increases the likelihood that topramezone treatments will be mixed with fungicide treatments. Previous research found that fungicides can reduce the activity of some herbicides, but their effects on topramezone efficacy are unknown. Four studies were established between Blacksburg, VA, and North Brunswick, NJ, in 2021 to determine whether chlorothalonil reduces goosegrass control from topramezone. In controlled environment dose-response studies the amount of topramezone needed to reduce goosegrass biomass by 50% increased from 3.04 g ha−1 to 5.27 g ha−1 when chlorothalonil (7,400 g ha−1) was added to the mixture. In field experiments, topramezone at 3.7 and 6.1 g ha−1 controlled goosegrass by 50% and 63%, respectively, at 42 d after treatment when averaged across herbicide admixtures. The addition of chlorothalonil alone and chlorothalonil plus acibenzolar-S-methyl to topramezone reduced goosegrass control from 73% to 52% and 45%, respectively, when averaged across topramezone rate. From these studies we can conclude that chlorothalonil has the potential to reduce goosegrass control when topramezone is applied at the maximum allowable rate (6 g ae ha−1) or less. This is the first report of fungicides acting to reduce herbicidal weed control efficacy in turfgrass systems.