Herbicide Interactions Research Articles

Light and temperature influence on diuron bioaccumulation and toxicity in biofilms.

Variations of temperature and photoperiod throughout different seasons can affect aquatic communities such as biofilms. Biofilms, generally present at the base of trophic chains in freshwaters, are also subject to organic contamination, and are especially affected by herbicides. Many studies have investigated the effect and interactions of herbicides and environmental factors on biofilms, but never with a toxicokinetic point of view. The objective of this study was to assess structural and functional changes in biofilms exposed to diuron, and to link them with contaminant accumulation, under the influence of temperature and light variations. To this aim, biofilms were exposed to all possible combinations of three concentrations (0, 5 and 50 µg L-1) of diuron, two temperatures (10 and 26 °C), and two light/dark photoperiods (16/8, 10/14), for durations of 0, 1 and 3 days. Diuron accumulation in biofilms was quantified and structural descriptors (protein and polysaccharide contents, dry weight) and functional endpoints (photosynthetic and enzymatic activities) were analyzed. The results obtained mainly highlighted the influence of temperature on diuron bioaccumulation and the associated toxic impact on biofilms. Bioaccumulation in biofilms exposed during three days at 10 °C, at the highest diuron concentration, was in average 1.4 times higher than bioaccumulation on biofilms exposed to 26 °C. Accordingly, the photosynthetic yield was more inhibited at lower than at higher temperatures. Temperature was also the highest impacting factor for metabolism regulation; for example, at 26 °C after three days of exposure, polysaccharide production was boosted under both photoperiods tested.

Barnyardgrass control using tank-mixed herbicides with saflufenacil and its influence in photosynthesis and chlorophyll fluorescence

ABSTRACT: The objectives of this research were to evaluate the interaction between herbicides mixed with saflufenacil for the control of barnyardgrass and to determine the effect on photosynthetic and chlorophyll fluorescence parameters. The experiment was conducted in a greenhouse in a 2x8 factorial scheme, whose factor A tested resistant and susceptible biotypes; and factor B the herbicides: saflufenacil (70 g a.i. ha-1), clomazone (180 g a.i. ha-1), imazapyr + imazapic (73.5 + 24.5 g a.i. ha-1), and cyhalofop (360 g a.i. ha-1), the mixtures of these herbicides with saflufenacil, and control without treatment. Weed control was assessed 7, 14, 21 and 28 days after herbicide application (DAA), as well as shoot dry matter at 28 DAA, photosynthetic parameters using infrared gas analyzer (IRGA), and emission of chlorophyll a fluorescence after 24 and 28 hours of application of treatments, respectively, and interaction of herbicides. Combination of saflufenacil with the herbicides tested in general did not change the response of both barnyardgrass biotypes to the herbicides used. The resistant biotype showed a lower negative effect on chlorophyll fluorescence and photosynthesis parameters in the combination of herbicides with saflufenacil. The herbicide cyhalofop was effective for the control of ALS-susceptible and resistant barnyardgrass.

What antagonistic interactions mean for Enlist and Roundup Ready Xtend technologies

AbstractThe commercialization of Roundup Ready Xtend and Enlist cropping systems increased the number of herbicide products available for postemergence application in soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.). A greater understanding of how glyphosate, glufosinate, dicamba, and 2,4‐D interact in mixture is needed. Two field experiments were conducted in 2015 and 2016 at the Northeast Research and Extension Center in Keiser, AR, to evaluate herbicide interactions that could occur in Enlist and Roundup Ready Xtend cropping systems. Various rates and combinations of glufosinate, glyphosate, dicamba, and 2,4‐D were applied and evaluated for percent weed control 5 wk after treatment (WAT). In the 2,4‐D experiment, glyphosate (dimethylamine salt) at 0.75 lb ae ac−1 provided 88% barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] control, whereas a premixture of glyphosate at 0.75 lb ae ac−1 + 2,4‐D at 0.70 lb ae ac−1 provided 80% control 5 WAT. Similarly, in the dicamba experiment, glyphosate (potassium salt) at 0.77 lb ae ac−1 provided 86% barnyardgrass control, compared to 79% with glyphosate at 0.77 lb ae ac−1 + dicamba at 0.5 lb ae ac−1. Antagonism was also identified for mixtures of glufosinate + glyphosate for barnyardgrass in both experiments. For Palmer amaranth (Amaranthus palmeri, S. Wats) and prickly sida [Sida spinosa (L.)] control, mixtures were generally equal to or greater than the individual herbicides alone, even though some mixtures were deemed antagonistic. Herbicide applicators in Roundup Ready Xtend or Enlist systems should be aware of antagonistic interactions and the implications of antagonism on herbicide resistance management.

Influence of weed size on herbicide interactions for Enlist™ and Roundup Ready® Xtend® technologies

AbstractWeed size can nfluence herbicide performance and herbicide interactions in mixtures. To control a broad range of species in soybean or cotton, POST herbicide mixtures will likely be commonplace in Roundup Ready® XtendFlex® and Enlist™ technologies. The impact of weed size on herbicide interactions that could occur in Roundup Ready XtendFlex or Enlist crops was assessed in two field experiments conducted in 2015 and 2016 at the Northeast Research and Extension Center in Keiser, AR. Combinations of glufosinate, glyphosate, dicamba, and 2,4-D were applied to either 10-cm or 30-cm weeds and evaluated for percent weed control, height reduction, and density reduction, collected 5 wk after treatment. Colby’s method was used to analyze treatments for herbicide interactions for control of barnyardgrass, Palmer amaranth, and pitted morningglory. Antagonism was identified with at least one treatment on all species. Almost all treatments were antagonistic for percent weed control, height reduction, and density reduction on barnyardgrass. When glyphosate in mixture with 2,4-D or dicamba was applied to 30-cm barnyardgrass, control declined 9% for both mixtures relative to glyphosate alone. Glufosinate plus glyphosate was antagonistic when applied to both 30-cm pitted morningglory and barnyardgrass. Glufosinate plus dicamba provided less control and density reduction of Palmer amaranth than what was expected from Colby’s equation. Overall, antagonism was more likely to be identified when applications were made to 30-cm weeds compared with 10-cm weeds. The utility of a given herbicide mixture will depend on the species present in the field and the size of those species at the time of application.

Isoxaflutole and metribuzin interactions in isoxaflutole-resistant soybean

AbstractHerbicide-resistant weeds are a growing concern globally; in response, new herbicide resistance traits are being inserted into crops. Isoxaflutole-resistant soybean [Glycine max (L.) Merr.] will provide a new mode of action for use in this crop. Ten experiments were conducted over a 2-yr period (2017, 2018) to determine herbicide interactions between isoxaflutole and metribuzin on soybean injury, weed control efficacy, and soybean yield on a range of soil types. Soybean leaf-bleaching injury caused by isoxaflutole was most severe at sites with higher levels of rainfall after application. Control of weed species with isoxaflutole (52.5, 79, and 105 g ai ha−1) and metribuzin (210, 315, and 420 g ai ha−1) differed by site based on amount of rainfall after application. At sites where there was sufficient rainfall for herbicide activation, isoxaflutole at all rates controlled common lambsquarters (Chenopodium album L.), Amaranthus spp., common ragweed (Ambrosia artemisiifolia L.), and velvetleaf (Abutilon theophrasti Medik.) >90%; metribuzin at all rates controlled Amaranthus spp. and witchgrass (Panicum capillare L.) >80%. Control of every weed species evaluated was reduced when there was limited rainfall after herbicide application. The co-application of isoxaflutole + metribuzin resulted in additive or synergistic interactions for the control of C. album, Amaranthus spp., A. artemisiifolia, A. theophrasti, Setaria spp., barnyardgrass [Echinochloa crus-galli (L.) P. Beauv], and P. capillare. Isoxaflutole and metribuzin can be an effective management strategy for common annual broadleaf and grass weeds in Ontario if timely rainfall events occur after herbicide application.

Analysis and DNA interaction of the profluralin herbicide

The increasing use of pesticides is a major health issue. There is therefore a need for improved analytical methods and more knowledge on the interaction of pesticides with living organisms. Here, we developed the analysis of profluralin in water and soils by cyclic voltammetry, square-wave voltammetry and square-wave adsorptive stripping voltammetry. We also studied the interaction between profluralin and double-stranded DNA. Results of cyclic voltammetric studies indicate that the reduction processes have an irreversible and adsorption-like character, as a possible consequence of the reduction of nitro groups of profluralin. Quantification was found linear from 60 to 800 nmol L−1 with a detection limit of 17 nmol L−1 using square-wave adsorptive stripping voltammetry. Results of interactions with double-stranded DNA from salmon sperm revealed that profluralin forms a complex with DNA by electrostatic binding. Values of Gibbs free energy confirmed that formation of profluralin–DNA complex is spontaneous and favourable.

Herbicide Interactions between Glufosinate and Three Fomesafen-Containing Herbicide Products as Affected by Weed Size and Spray Droplet Size

Herbicide Interactions between Glufosinate and Three Fomesafen-Containing Herbicide Products as Affected by Weed Size and Spray Droplet Size

Interaction Between Saflufenacil and Other Oxidative Stress Promoting Herbicides to Control Wild Poinsettia

ABSTRACT: Synergism is a desired result in the interaction between herbicides because it provides many benefits, among which the reduction of doses and the increment of control efficiency, and because it positively signals for the joint application of herbicides. The objective of this study is to evaluate the effect of the association of saflufenacil with other herbicides that promote oxidative stress on the development of Euphorbia heterophylla as well as to analyze if the resulting interactions are antagonistic, additive or synergistic. The experiment was conducted in pots, in a greenhouse, using a completely randomized design with four replications. Treatments consisted of saflufenacil (0, 1,2, 2,32, 4,47, 8,63, 16,65 g ha-1) alone and associated with clomazone (288 and 504 g ha-1), metribuzin (105.6 and 206.4 g ha-1) and paraquat (20 and 40 g ha-1), as well as these herbicides applied alone at the same doses described above. Twenty-one days after the application (DAA), the shoot dry matter (SDM) of plants was evaluated in each experimental unit. The Limpel-Colby method was used to calculate the expected response of the herbicide interaction. All combinations of saflufenacil with clomazone, metribuzin and paraquat were considered synergistic. Among the treatments associated with saflufenacil, those including metribuzin at the dose of 105.6 g ha-1 were the ones that provided the most promising results, which stood out for the greater reductions of wild poinsettia shoot dry matter, compared to the application of saflufenacil alone.

Opposite effects of mixtures of commercial formulations of glyphosate with auxinic herbicides on the ten spotted live-bearer fish Cnesterodon decemmaculatus (Pisces, Poeciliidae)

We analyzed the acute toxicity of the 48% glyphosate (GLY)-based Credit®, the 57.71% dicamba (DIC)-based Kamba®, and the 83.5% 2,4-dichlorophenoxyacetic acid (2,4-D)-based Weedar® Full, alone and as mixtures on the fish Cnesterodon decemmaculatus. Mortality revealed the LC50 96h values of 91.73 mg L−1 (range: 86.80–98.00 mg L−1), 1401.57 mg L−1 (range: 1243.78–1527.35) and 678.04 mg L−1 (range: 639.35–718.04 mg L−1) for GLY, DIC and 2,4-D, respectively. Mean values for the toxic unit (TU) that induced 50% mortality (TU50 96h) of fish exposed to equitoxic mixtures were 1.67 (range: 1.65–1.69) for Credit® and Kamba® and 1.28 (range: 1.20–1.36) for Credit® and Weedar® Full suggesting that both mixtures are antagonic. Non-equitoxic combinations demonstrated an antagonistic interaction of herbicides Credit® and Kamba®, whereas a synergistic effect was observed for Credit® and Weedar® Full formulations. GLY and DIC as a mixture demonstrated lower toxicity on non-target species compared to GLY and 2,4-D in combination, at least for C. decemmaculatus, leading to the conclusion that the former combination could be strongly recommended in further agricultural practices.

Towards a better understanding of agronomic and soil basis for possible charcoal root rot control and production improvement in bean

Macrophomina phaseolina causes charcoal root rot (CRR) in numerous crops worldwide. However, structural progression of CRR epidemics in association with bean agro-ecosystems is little understood. Thus, progression of CRR epidemics in interaction with 13 agro-ecological variables was characterised in 48 commercial bean fields. Frequency of pathogen isolated from root was assessed at vegetative (V3), flowering-podding (R6-7) and pod maturity (R9) growth stages. Two principal factors accounting for 89% of total data variance characterised CRR epidemics. Rhizobial nodulation and cultivation–depth, clay–pH, date–preceding crop, urea–bean class and urea–herbicide interactions accounted for 50% CRR epidemic dynamics. Sixty-five percent of production variance was explained by soil clay, bean class, colonisation, planting date and depth, cultivation method, preceding crop, nodulation, herbicide and urea application. The present findings enabled us to explain a noticeable part of variations in productivity among the bean CRR pathosystems with the help of certain agricultural and environmental events for sustainable agriculture purposes.

Reduced Translocation of Glyphosate and Dicamba in Combination Contributes to Poor Control of Kochia scoparia: Evidence of Herbicide Antagonism

Kochia scoparia is a troublesome weed across the Great Plains of North America. Glyphosate and dicamba have been used for decades to control K. scoparia. Due to extensive selection, glyphosate- and dicamba-resistant (GDR) K. scoparia have evolved in the USA. Herbicide mixtures are routinely used to improve weed control. Herbicide interactions if result in an antagonistic effect can significantly affect the management of weeds, such as K. scoparia. To uncover the interaction of glyphosate and dicamba when applied in combination in K. scoparia management the efficacies of different doses of glyphosate plus dicamba were evaluated under greenhouse and field conditions using GDR and a known glyphosate- and dicamba-susceptible (GDS) K. scoparia. The results of greenhouse and field studies suggest that the combination of glyphosate and dicamba application controlled GDS, but glyphosate alone provided a better control of GDR K. scoparia compared to glyphosate plus dicamba combinations. Furthermore, investigation of the basis of this response suggested glyphosate and dicamba interact antagonistically and consequently, the translocation of both herbicides was significantly reduced resulting in poor control of K. scoparia. Therefore, a combination of glyphosate plus dicamba may not be a viable option to control GDR K. scoparia.

Reduced Translocation Is Associated with Antagonism of Glyphosate by Glufosinate in Giant Foxtail (Setaria faberi) and Velvetleaf (Abutilon theophrasti)

Previous reports have underscored antagonism that may result from mixing glyphosate and glufosinate across a wide range of application rates and for various broadleaf and grass weed species, but no investigation has been conducted to characterize glyphosate absorption and translocation when combined with glufosinate. The objectives of this study were to evaluate herbicide efficacy and assess herbicide interaction and physiological response with combinations of glyphosate and glufosinate on common lambsquarters, velvetleaf, and giant foxtail. Greenhouse studies to determine interaction resulted in strong and persistent antagonism between glyphosate at 110 and 220 g ae ha−1and glufosinate at 20 or 40 g ae ha−1in giant foxtail, whereas only transient and reduced antagonism was noted for velvetleaf and common lambsquarters. Combining glyphosate and glufosinate increased the maximum absorption of glyphosate by 9% and 23% in velvetleaf and giant foxtail, respectively, compared with glyphosate alone. In velvetleaf, averaged over time, only 2.6% of the applied radioactivity translocated out of the treated leaf when glufosinate was mixed with glyphosate compared with 9.9% when glyphosate was applied alone. In giant foxtail, 21.6% of the [14C]glyphosate translocated out of the treated leaf when glufosinate was mixed with glyphosate compared with 52.4% when glyphosate was applied alone. Conversely, no change in the radioactive pattern of translocation was noted for common lambsquarters. These results suggest that reduced translocation of glyphosate is the physiological mechanism responsible for the antagonism observed between glyphosate and glufosinate in giant foxtail and, to a lesser extent, in velvetleaf.

Environmental Factors Moderate Glyphosate-induced Antagonism of POST Herbicides on the Rapid Response Biotype of Glyphosate-Resistant Giant Ragweed (Ambrosia trifida)

AbstractIn the rapid response (RR) biotype of glyphosate-resistant (GR) giant ragweed (Ambrosia trifidaL.), exposure to glyphosate elicits H2O2production in mature leaves, resulting in foliage loss and reduced glyphosate translocation. When glyphosate is applied with POST herbicides intended to improve control ofA. trifida, the RR to glyphosate has the propensity to antagonize these herbicide combinations. This research documents how transient changes in air temperature, soil moisture, and light intensity during a 6-d period surrounding herbicide application regulate induction of the RR and the effect on POST herbicide interactions with glyphosate. Air temperature had the greatest influence on H2O2accumulation in leaf disks following treatment with glyphosate, as plants at 30 C produced more than twice the amount of H2O2at 2.5 h after treatment compared with 10 C. Plants under field capacity conditions accumulated nearly 50% more H2O2than those at one-third field capacity, while those under no shade had only 18% more H2O2compared with those in a shaded environment. Despite these initial results, dry weight reduction at 21 d after treatment never differed by more than 8% between levels of environmental factors, thus indicating a negligible influence on glyphosate efficacy. The magnitude of glyphosate-induced antagonism was generally greater at 30 C (12% to 21% less than expected control) versus 10 C (11% to 16%) on atrazine, cloransulam, dicamba, and topramezone and was greater at field capacity (20% to 24%) versus one-third field capacity (11% to 15%) on cloransulam and topramezone. These results indicate air temperatures and soil moisture levels conducive to optimal plant growth accelerate the RR to glyphosate, thereby increasing the likelihood of glyphosate-induced antagonism on several translocated herbicides.

Persistence of acetochlor, atrazine, and S-metolachlor in surface and subsurface horizons of 2 typic argiudolls under no-tillage.

Variations in soil properties with depth strongly influence the degradation and persistence of herbicides, underlining the importance of studying these processes in soil horizons with distinctively different properties. The persistence of the herbicides acetochlor, atrazine, and S-metolachlor was measured in samples of the A, B, and C horizons of 2 Typic Argiudolls from Argentina under no-till management. The soils studied differed in soil organic carbon (OC) content, pH, particle size distribution, and structure. Quantification of herbicides in soil was done through high-performance liquid chromatography with diode array detector. There were interactions of herbicide × horizon (p < 0.01) that resulted in degradation rates (k) of all herbicides decreasing, and their corresponding dissipation half-life (DT50) values increasing, with soil depth. Herbicide persistence across all soils and horizons ranged from 15 to 73 d for acetochlor, 13 to 29 d for atrazine, and 82 to 141 d for S-metolachlor, which had significantly (p < 0.01) greater persistence than atrazine and acetochlor. The DT50 values of herbicides were negatively correlated with the contents of OC (correlation coefficients ranging from -0.496 to -0.773), phosphorus (-0.427 to -0.564), and nitrogen-nitrate (-0.507 to -0.662), and with microbial activity (-0.454 to -0.687) and the adsorption coefficient (-0.530 to -0.595); DT50s were positively correlated with pH (0.366 to 0.648). Adsorption was likely the most influential process in determining persistence of these herbicides in surface and subsurface horizons. The present study can potentially improve the prediction of the fate of acetochlor, atrazine, and S-metolachlor in soils because it includes much needed information on the degradation of the herbicides in subsurface horizons. Environ Toxicol Chem 2017;36:3065-3073. © 2017 SETAC.

Herbage Mass and Nutritive Value of Bermudagrass Influenced by Non‐Growing‐Season Herbicide Application

Core Ideas Dormant‐season herbicide applications are effective in controlling cool‐season weeds in bermudagrass. Some dormant‐season herbicide products can negatively impact bermudagrass forage production. Dormant‐season application of glyphosate did not cause significant damage to the bermudagrass stand. Elimination of cool‐season weeds in bermudagrass may not always be advantageous. Application of herbicides to dormant bermudagrass [Cynodon dactylon (L.) Pers] in late winter to control cool‐season weeds is a possible management practice for more marketable hay harvests. The objective of this study is to determine dormant‐season herbicide effects on bermudagrass herbage mass and nutritive value at four harvest dates typical for Louisiana. The experimental design was a randomized complete block of Roundup (glyphosate), Plateau (imazapic), Journey (imazapic + glyphosate), Pastora (nicosulfuron + metsulfuron methyl), and a control (no herbicide treatment). The treatments were applied mid‐February of 2013 and 2014. Cool‐season weeds contain lower neutral detergent fiber (NDF) concentration than bermudagrass while containing higher acid detergent fiber (ADF), crude protein (CP), and in vitro dry matter digestibility (IVDMD). Pastora resulted in the highest bermudagrass composition of 65.2% (DM basis) at the first harvest, followed by Journey, Plateau, Roundup, and control treatment with 44.2, 33.6, 28.3, and 20.7%, respectively. Herbicide × harvest interaction was significant for herbage accumulation and nutritive value. Pastures receiving Pastora and Journey accumulated less herbage with lower CP concentration than pastures receiving Roundup and control due to lower weed composition. Year × herbicide interaction was significant and herbage mass from Pastora treated pasture was lower in 2014 than 2013. It was concluded that dormant‐season herbicide applications may be beneficial for producing a weed‐free first harvest of bermudagrass hay, but may sacrifice some nutritive value provided by the inclusion of cool‐season herbage mass, grass, and broadleaf weeds, in the harvested product.

Potential Interaction of Pre-emergence Herbicides and the Efficacy of Insecticide and Fungicide Seed Treatments in Cotton

The increasing presence of glyphosate-tolerant weeds has increased the use of pre-emergence herbicides in cotton, Gossypium hirsutum L., grown in Tennessee during the last 5 to 8 years. These herbicides could have negative effects on seedling growth and potentially affect thrips (Thysanoptera: Thripidae) management or seedling disease with at-planting insecticides or fungicides. Experiments were conducted in 2013 and 2014 to evaluate the potential interactions of pre-emergence herbicides on the efficacy of insecticide or fungicide seed treatments in cotton. Nontreated plots and plots treated with a thiamethoxam seed treatment generally exhibited higher number of thrips, more thrips injury, less vigor, delayed maturity, and lower yields compared to plots treated with an imidacloprid seed treatment or an in-furrow application of aldicarb. Similarly, fungicide seed treatments generally reduced the incidence of seedling disease (primarily Rhizoctonia), while improving seedling health and stand density. Negative effects of some pre-emergence herbicides on plant health also were observed. For example, combination treatments of fluometuron plus S-metolachlor or fluometuron plus fomesafen reduced plant vigor and seedling biomass and there was a tendency for higher thrips populations where pre-emergence herbicides were used. There were no substantial interactions between injury caused by pre-emergence herbicides and that caused by thrips or seedling disease suggesting that thrips, seedling disease, and herbicide injury acted independently and additively. Following herbicide label rates should reduce the risk of compounding the effects of thrips or seedling disease with herbicide injury.

Interaction of chiral herbicides with soil microorganisms, algae and vascular plants.

Chiral herbicides are often used in agriculture as racemic mixtures, although studies have shown that the fate and toxicity of herbicide enantiomers to target and non-target plants can be enantioselective and that herbicide toxicity can be mediated by only one enantiomer. If one enantiomer is active against the target plant, the use of enantiomer-rich herbicide mixtures instead of racemic herbicides could decrease the amount of herbicide applied to a crop and the cost of herbicide application, as well as unintended toxic herbicide effects in the environment. Such a change in the management of herbicide applications requires in-depth knowledge and a critical analysis of the fate and effects of herbicide enantiomers in the environment. This review article first synthesizes the current state of knowledge on soil and plant biodegradation of herbicide enantiomers. Second, we discuss our understanding of the biochemical toxicity mechanisms associated with both enantiomers in target and non-target plants gained from state-of-the-art genomic, proteomic and metabolomic tools. Third, we present the emerging view on the "side effects" of herbicides in the root microbiome and their repercussions on target or non-target plant metabolism. Although our review of the literature indicates that the toxicity of herbicide enantiomers is highly variable depending on plant species and herbicides, we found general trends in the enantioselective toxic effects of different herbicides in vascular plants and algae. The present study will be helpful for pesticide risk assessments as well as for the management of applying enriched-enantiomer herbicides.

Interactions of Saflufenacil with Other Herbicides Promoters of Oxidative Stress to Control Joyweed1

ABSTRACT This study was conducted to evaluate the efficacy of joyweed (Alternanthera tenella) control and antagonistic or synergistic potentials of saflufenacil herbicide applied alone or tank mixed with paraquat, metribuzin and clomazone. The experiment was conducted in a greenhouse in a completely randomized design with four replications. Treatments consisted of saflufenacil herbicide doses (0, 0.4, 0.7, 1.4, 2.1 and 2.8 g ha-1) applied isolated or associated with paraquat (0, 1 and 3 g ha-1), metribuzin (0, 38.4 and 105.6 g ha-1) or clomazone (0, 288 and 504 g ha-1). Visual control was determined at 14 and 21 days after spraying the herbicides (DAA) and shoots dry matter at 21 DAA. Colby's method was used to calculate the response from herbicide interactions. Saflufenacil associations with paraquat and metribuzin were promising to control A. tenella, due to the high levels of control achieved and because they demonstrated compatibility, especially in some combinations. Tank mixing saflufenacil with clomazone was not promising for the control of A. tenella due to the low efficacy of joyweed control and because it demonstrated herbicide incompatibility.

Effect of different glyphosate salts on phosphodiesterase and phosphotriesterase activities in soil with reference to ecological importance of soil pollution. A laboratory experiment

Abstract The aim of this study is to determine the effect of the two glyphosate salts: isopropylamine and potassium (contained in preparations Roundup) on the activity of phosphodiesterase and phosphotriesterase in the soil. The experiment was carried out in the laboratory conditions on two soil types: loamy sand (Corg 8.70 g·kg−1, pHKCl 6.39) and sandy loam (Corg 10.90 g·kg−1, pHKCl 6.81). Two glyphosate salts (isopropylamine and potassium) in dosage of 0, 1 and 100 mg·kg−1 were applicate into soils. Phosphodiesterase and phospotriesterase activities in soils were determined spectrophotometrically on days 1, 7, 14, 28, 56 and 112. The obtained results were converted with respect to the enzyme activities in the control soil (assuming it to be 100%) and given as percent of inhibition. The results were shown as environmental danger zones graphs. Obtained results showed that glyphosate salts application has primarily resulted in inhibition of phosphodiesterase activity, and stimulation of phosphotriesterase activity in soils. Soil type and kind of glyphosate salt affect the interaction of herbicide with phosphodiesterase and phosphotriesterase activities. The observed changes in the phosphodiesterase and phosphotriesterase activities caused by the addition of both glyphosate salts were located on environmental danger zones graphs in the range of negligible or acceptable values, which may indicate a low impact of herbicide on measured enzymes.

Interactions of triazine herbicides with biochar: Steric and electronic effects

We studied the adsorption of triazine herbicides and several reference heteroaromatic amines from water onto a temperature series of hardwood biochars (300–700 °C, labeled B300–B700). Adsorption on biochars correlated poorly with pyrolysis temperature, H/C, O/C, mean minimum fused ring size, surface area (N2 or CO2), microporosity, and mesoporosity, but correlated well with a weighted sum of microporosity and mesoporosity. Steric effects were evident by the negative influence of solute molecular volume on adsorption rate. For a given compound, adsorption rate maximized for the biochar with the greatest mesoporosity-to-total-porosity ratio, suggesting that mesopores are important for facilitating diffusion into pore networks. The cationic forms of amines adsorb more slowly than the neutral forms. To further probe steric and electronic effects, adsorption on a biochar (B400) was compared to adsorption on graphite—a nonporous reference material with an unhindered, unfunctionalized graphene surface—and in comparison with reference compounds (benzene, naphthalene, pyridine, quinoline and 1,3-triazine). Relative to benzene, the surface area-normalized adsorption of the triazine herbicides was disfavored on B400 (favored on graphite) by 11–19 kJ/mol, depending on concentration. It is estimated that steric suppression of B400 adsorption comprises 6.2 kJ/mol of this difference, the remainder being the difference in polar electronic effects. Based on the behavior of the reference amines, the difference in polar effects is dominated by π−π electron donor–acceptor (EDA) interactions with sites on polyaromatic surfaces, which are more electropositive and/or more abundant on graphite. Overall, our results show that mesoporosity is critical, that adsorption rate is a function of solute molecular size and charge, that steric bulk in the solute suppresses equilibrium adsorption, and that π−π EDA forces play a role in triazine polar interactions with biochar.