Glyphosate Application Research Articles

Synergistic effect of pyridate-based herbicide mixtures for controlling multiple herbicide-resistant kochia

Abstract Multiple herbicide classes resistant (MHCR) kochia poses a serious concern for producers in the Central Great Plains, including western Kansas. Greenhouse and field experiments were conducted at Kansas State University Research and Extension Centers near Hays and Garden City, KS to evaluate pyridate-based postemergence (POST) herbicide mixtures for controlling MHCR kochia. One previously confirmed MHCR population (resistant to atrazine, glyphosate, dicamba, and fluroxypyr) and a susceptible (SUS) kochia population were tested in a greenhouse study. The kochia population at Hays field site was resistant to atrazine, dicamba, and glyphosate while kochia population at Garden City site was resistant to atrazine and glyphosate. Colby’s analysis revealed synergistic interactions when pyridate was mixed with atrazine, dicamba, dichlorprop-p, fluroxypyr, glyphosate, or halauxifen/fluroxypyr and resulted in ≥94% control and shoot dry biomass reduction of MHCR kochia in a greenhouse study. Similarly, synergistic interactions were observed for MHCR kochia control in fallow field studies at both sites when pyridate was mixed with glyphosate or atrazine. Kochia control was increased from 26% to 90% with the application of glyphosate + pyridate and from 28% to 95% with atrazine + pyridate at both sites as compared to separate applications of glyphosate or atrazine. This is the first report for such a strong synergistic effect for both glyphosate and atrazine mixtures with pyridate on a weed resistant to both. All other pyridate-based herbicide mixtures showed an additive interaction and resulted in better control of MHCR kochia (87 to 100%) as compared to their individual applications (23 to 92%) across both sites except 2,4-D. These results suggest that pyridate can play a crucial role in various POST herbicide mixtures for effective control of MHCR kochia.

Winter leaf phenology differences facilitate selective control of an invasive plant species by herbicide

Herbicide control of invasive plant species is generally efficient. However, there is a likelihood of the excessive application of non-selective herbicides that kill co-occurring native species and cause environmental toxicity. We present a case study on the control of the invasive exotic Solidago canadensis with photosynthetically active leaves in winter by applying glyphosate. This approach improves herbicide control efficiency, while preventing harm to most co-occurring native plants. We quantified the winter leaf phenology and photosynthetic capacity of S. canadensis and two commonly co-occurring native species. We tested the effects of glyphosate and competition on S. canadensis and native Imperata cylindrica with contrasting winter leaf phenology in both pot and field experiments. Finally, we surveyed the life forms and winter leaf phenology of most co-occurring plant species in eastern China to determine whether most co-occurring species and S. canadensis differ in winter leaf phenology. Old leaves withered much later and new leaves developed much earlier in S. canadensis than in the two co-occurring species. Both the old and new leaves of S. canadensis had high photosynthetic capacity in winter. In summer, glyphosate suppressed the growth of S. canadensis by 20.1–59.5% and growth of I. cylindrica to a greater extent (by 57.6–91.7%), whereas winter application of glyphosate at a certain concentration suppressed the growth of S. canadensis by 91.4–95.6% (the efficiency was higher than summer application), but had no impact on I. cylindrica. Glyphosate application in winter alleviated competition stress from S. canadensis on I. cylindrica. We conclude that winter glyphosate application can increase the selectivity and efficiency of chemical control of invasive S. canadensis, which may shift the competition balance towards native species and favour native vegetation recovery in sites invaded by S. canadensis. The principles of this approach can be applied to any scenario where invasive species and co-occurring species have distinct phenological niche separation.

Effect of Biostimulants and Glyphosate on Morphophysiological Parameters of Zea mays (L.) Seedlings Under Controlled Conditions

Maize (Zea mays L.) is the major produced crop in South Africa, but numerous abiotic/biotic stressors threaten its production. Herbicides are mainly in the agricultural sector to minimise crop yield losses caused by weed competition. However, with most weeds becoming resistant to glyphosate, South African farmers have used higher herbicide concentrations than typically recommended. This study was conducted to determine the effect of two biostimulants (brassinosteroids and KELPAK) and glyphosate on the morphophysiological parameters of maize seedlings. Experiments were carried out in the glasshouses of the Department of Soil, Crop, and Climate Sciences at the University of the Free State in Bloemfontein for eight weeks over two seasons, 2017/2018 and 2018/2019. The treatments did not significantly affect all maize morphological parameters except the plant dry mass. Compared to the control, plant dry mass was significantly (p < 0.05) increased by 15.72 g when glyphosate was applied in combination with brassinosteroids during the 2019 growing season. The application of glyphosate, brassinosteroids, and KELPAK differed significantly (p < 0.05) between weeks across the physiological parameters in the two seasons: an irrefutable significant increase was recorded in the rates of transpiration between the weeks. Although significant differences were recorded in the chlorophyll fluorescence, chlorophyll, and carotenoid content, these parameters were similar to the control, especially in the last week of data collection. During the early developmental stage of maize, farmers can administer biostimulants—brassinosteroid (5 g ai ha−1) and KELPAK (5% ai ha−1)—alone and in combination in glyphosate-resistant maize cultivars treated with glyphosate to aid maize seedlings.

Glyphosate Resistance in Eleusine indica: Involvement of CYP71AK44 in Addition to EPSPS Gene Overexpression.

Intensive application of glyphosate has resulted in resistance evolution in many weed populations, including Eleusine indica. This study characterized glyphosate resistance and investigated the underlying mechanisms in a glyphosate-resistant population (R-JX) of E. indica from China. The R-JX population was 8.5 times resistant to glyphosate relative to the glyphosate-susceptible population (SA). Point mutations were not observed in the target gene 5-enolypyruvyl-shikimate-3-phosphate synthase gene (EPSPS). However, the expression level and copy number of EPSPS were 8.8 times and 15.2 times, respectively, greater in R-JX than that in the SA population. Pre-application of the P450 inhibitor lowered the resistance level to glyphosate from 8.5 times to 3.6 times in the R-JX population. RNA-Seq and RT-qPCR revealed that the CYP71AK44 gene was consistently upregulated in R-JX and five other glyphosate-resistant populations. Rice calli and seedlings overexpressing CYP71AK44 showed glyphosate resistance. In conclusion, overexpression of the target EPSPS plus CYP71AK44 collectively contributes to glyphosate resistance in these E. indica populations.

Seasonal comparison of household vinegar and glyphosate treatments on Microstegium vimineum removal in the North Carolina, United States piedmont

Microstegium vimineum, or Japanese stiltgrass, is an invasive species that readily outcompetes native vegetation and is of poor forage quality for wildlife. This species is widespread throughout the southeastern United States, including North Carolina. Much of this region is privately owned and there is a gap in the literature providing succinct information about the best methods of treatment, timing of treatment, and effects of treatment on native herbaceous plants in this region. This study seeks to address this gap by evaluating two treatments that are easily accessible to landowners (glyphosate and vinegar) applied at three intervals throughout the growing season to assess the effects on M. vimineum removal and the herbaceous plant community. We found that glyphosate application was the most effective treatment, removing nearly 100% of M. vimineum but resulting in less diverse herbaceous communities. In contrast, vinegar application was both effective (54.9 ± 2.7% M. vimineum removal) and maintained species richness and diversity. Timing of applications did not affect treatment efficacy or plant diversity for either treatment. This study provides evidence that vinegar is an effective substitute for synthetic herbicides and can support M. vimineum removal efforts while maintaining plant diversity.

Glyphosate application may influence the transfer of trace elements from soils to both soil solutions and plants

Trace elements dynamics in the soil-plant system depends on multiple parameters, including chelating organic compounds from natural or synthetic organic matters. In this study, we evaluated the influence of one of the most common pesticides—glyphosate—on the mobility of trace elements considering contrasted soils (uncontaminated, anthropogenically contaminated, and naturally-enriched) in a greenhouse experiment. Four modalities have been tested: one control without any application, two with different glyphosate doses (1 and 3 times the authorised field dose), and one with compost addition to evaluate its potential ability to mitigate the impact of glyphosate on trace element mobility. Both, trace element and glyphosate concentrations were measured in the soil solutions and trace element contents were determined in plants at the end of the experiment. The results showed that, although glyphosate concentrations rapidly decreased in soil solutions, glyphosate application still influenced the transfer of trace elements to both soil solution (up to 12-times higher) and plant (up to 5.2-times higher). This influence was highly dependent on both the specific elements and the type of soils considered. For instance, in uncontaminated soils, glyphosate especially increased the mobilization of Mn, Co, Zn, Mo, and Pb to soil solution. This effect diminished of 2.5 times on average with increasing soil contamination. A similar trend was observed for the transfer of trace elements from soil to plant (i.e., on average 2.2-times lower in the most contaminated compared to the uncontaminated soil). However, in the naturally-enriched soil, opposing trends were noted between soil solutions and plants. The impact of compost addition on the transfer of trace elements to plants remains unclear: compost enhanced the transfer of trace elements to soil solution in uncontaminated and naturally-enriched soils likely due to trace element input through the compost, but decreased the transfer in anthropogenically-contaminated soils likely due to adsorption processes. Therefore, glyphosate could potentially increase the exposure of trace elements through food consumption and their transfer to the ecosystem, particularly in uncontaminated and weakly contaminated soils. In highly contaminated soils, compost could mitigate the glyphosate-induced enhancement of trace element mobility to soil solutions.

The response of microbiome assembly within different niches across four stages to the cultivation of glyphosate-tolerant and conventional soybean varieties.

Plants are inherently connected with the microbiome, which plays a crucial role in regulating various host plant biological processes, including immunity, nutrient acquisition, and resistance against abiotic and biotic stresses. Many factors affect the interaction between plants and microbiome. In this study, microbiome samples were collected from five niches (bulk soil, rhizoplane, root endosphere, phylloplane, and leaf endosphere) across four developmental stages (seedling, flowering, podding, and maturity) of various soybean varieties. Composition and structure of bacterial and fungal communities were analyzed using 16S rRNA gene and ITS (Internally Transcribed Spacer) region amplicon sequencing. It was observed that both niches and developmental stages significantly impact on the assembly and composition of soybean microbiome. However, variety, presence of a transgene, and glyphosate application had minimal effects on microbial communities. The dominant microbiome varied across the five niches, with most containing beneficial microbial communities capable of promoting plant growth or increasing disease resistance. Types and abundance of the dominant microbes affected network stability, potentially resulting in functional changes in different ecological niches. This study provides theoretical evidence for microbial protection of plants against diseases and demonstrates that systematic analysis of the composition and diversity of soybean microbiomes can contribute to the development of biological control technologies.

Effects of transgenic modification on the bacterial communities in different niches of maize under glyphosate toxicity

Transgenic glyphosate-resistant maize has emerged as a way to expand the use of glyphosate for weed control. Studying the microbiome in the tissues and rhizosphere soil of transgenic plants is vital for understanding the glyphosate-resistant mechanism and optimizing the transgenic design of crops. In our study, the expression of a mutant cp4epsps gene in transgenic maize, which confers tolerance to glyphosate, was performed using the maize variety Xianyu 335 as the genetically modified acceptor line. This transgenic modification did not affect the initial bacterial community in the leaf, stem, or root of maize, but promoted a differential bacterial community in the rhizosphere soil. Under glyphosate application, the abundance of beneficial bacteria involved in N fixation and P solubilization in plant tissues and the rhizosphere soil of glyphosate-resistance maize were higher than those in the glyphosate-sensitive maize. In contrast, the abundance of pathogens had the opposite trend, suggesting that the enhanced health of transgenic maize prevented microbiome deterioration under glyphosate. The re-inoculation of bacterial strains isolated from glyphosate-resistance maize into the leaf and rhizosphere soil of glyphosate-sensitive maize resulted in an enhanced photosynthetic capacity in response to glyphosate, demonstrating the vital role of specific bacteria for glyphosate resistance. Our study provides important evidence of how transgenic maize tolerance to herbicides affects the bacterial communities across the maize niches under glyphosate toxicity.

Glyphosate isolado e em associação com herbicida para o controle e seletividade de plantas daninhas na cultura do algodão RF

Cotton (Gossypium hirsutum L.) is a fiber-producing plant that demonstrates high cultivation aptitude in Brazil. However, crop performance is influenced by factors such as weed interference, mainly due to the few options of selective herbicides to be applied in post-emergence in cotton cultivars with RF technology. Thus, the objective of this study was to evaluate the use of glyphosate associated with latifolicides for weed management in cotton crops. For this, a field experiment was carried out, in a randomized block design with 13 tracts and four replications, using cv. Deltapine DP1857B3RF. The treatments were composed of pyrithiobac-sodium at doses (36.4, 42.0 and 50.4 g a.i. ha-1), trifloxysulfuron-sodium (2.25, 2.62 and 3.0 g a.i. ha-1), glyphosate isopropylamine salt and potassium (1,350 and 1,512 g a.i. ha-1) used separately and together, with two deposition formats, in total area and directed jet, and two controls, one without any control method and the other weeded control. The association between the herbicides and the joint application of the three herbicides provided efficiency above 95% of control for volunteer soybean plants. The mixture of pyrithiobac-sodium and trifloxysulfuron-sodium (42.0 + 3.0 g a.i. ha-1), followed by sequential applications of glyphosate (1,512 g a.i. ha-1), regardless of the form of deposition of the herbicide, provided control above 95%, at 45 days after the first application, for the goosegrass (Eleusine indica) and viola-string (Ipomoea sp) plants. Symptoms of injury were observed in cotton plants, with greater intensity until 15 days after application (DAA), when pyrithiobac-sodium, trifloxysulfuron-sodium and glyphosate (36.4 + 2.25 + 1,350 g a.i. ha-1) were associated, reaching 35.5 % of the affected plants. Plant height was initially affected by the triple association between the herbicides pyrithiobac-sodium, trifloxysulfuron-sodium and glyphosate (36.4 + 2.25 + 1,350 g a.i. ha-1), however, at 90 DAA, all treatments provided higher plant height than the control without herbicide intervention, which was 95.3 cm. For boll weight, no difference was observed between the treatments, other than fiber yield, being lower for the treatments in which glyphosate was associated with pyrithiobac-sodium and trifloxysulfuron-sodium, providing 38.8 and 39.1%, respectively. Cotton yield was influenced by treatments where trifloxysulfuron-sodium was applied associated with glyphosate (2.62 + 1,350 g a.i. ha-1) and pythiobac-sodium, trifloxysulfuron-sodium and glyphosate (36.4 + 2.25 + 1,350 g a.i. ha-1), followed by glyphosate application at 43 DAE, but all treatments were superior to the control without herbicide application. Glyphosate applied alone or in association was essential for weed management in cotton production systems with RF technology.

Effects of Mulching and Flaming on Weed Control and Almond Growth in a Newly Established Almond Orchard

This study was conducted in a newly established (2-year-old) almond orchard to investigate the effects of five different mulching materials (woven and nonwoven fabric, black and white polyethylene, almond shell) and flame treatments applied at two different frequencies (FL20 and FL30) on weed control and almond growth compared with those of conventional herbicide (glyphosate) application and weedy control. Thus, this study included nine different treatments. The impacts of these treatments on weed density and coverage were periodically monitored. Additionally, the biomass of the weeds was measured at the end of the season to evaluate the effects of the treatments. Because the almond orchard was not yet in the economic fruit-bearing stage, the effects of the treatments were examined in terms of parameters that characterize almond growth, such as plant height, trunk diameter, shoot length, and shoot thickness. The chlorophyll content and water potential values of the trees were also determined. The results of this two-season study indicated that synthetic mulches provided the best outcomes in terms of weed control and almond growth. No weed emergence was observed throughout the season in any of the synthetic mulch treatments. Although almond shells used as organic mulch were highly effective for blocking sunlight, they failed to prevent the growth of some vigorously growing perennials such as Cynodon dactylon and Sorghum halepense that emerged from gaps. Flame treatments demonstrated rapid and effective results; however, they were less successful against the aforementioned monocot perennial weeds and required frequent repetition because of the lack of residual effects. Glyphosate, an herbicide that is commonly used in conventional orcharding, was applied five times throughout the experiment and proved effective weed management compared with that of the weedy control. However, considering the increasing herbicide resistance, environmental and health issues, and growing interest in organic almond cultivation, synthetic mulch applications have emerged as good options. Despite the initially higher establishment costs, synthetic mulches effectively controlled weeds and reduced water stress, thereby promoting almond tree growth.

Effects of different timing and rate of glyphosate application on the residue level, grain quality, and processing performance of two Canadian malting barley varieties

AbstractBackground and ObjectivesA preharvest application of glyphosate on malting barley can assist in the management of perennial weed growth before harvest and serves as a harvest aid by drying down the crop. The main objective of this study was to assess the effects of preharvest glyphosate application at two glyphosate rates (900 or 1125 g ae/ha) and three application timings based on the maturity and seed moisture level (soft dough, hard dough, or mature).FindingsThe levels of glyphosate residue in barley grain were highly variable among locations and years ranging from 0 to 95 mg/kg. Glyphosate application at both rates at the soft dough stage significantly decreased the kernel weight of barley grain. Barley grain with up to 40 mg/kg of glyphosate residue exhibited adequate germination energy required for malting purposes; however, the residue negatively affected the growth of roots during the malting process. The levels of α‐amylase in malt decreased with increasing levels of glyphosate residue in barley. Other malt and wort parameters were generally not affected by the glyphosate application on barley.ConclusionsToo early application of glyphosate at the soft dough stage of barley grain development reduced the kernel weight and size, interfered with roots production, affected synthesis of α‐amylase, and reduced the malt extract in several cases.Significance and NoveltyResults indicated that in the majority of environments, when glyphosate was applied at the recommended stage and rate, neither the maximum residue limit was exceeded nor were the germination and malting quality of barley impaired. In real farming conditions, it might be hard to achieve similar results despite adherence to the recommended timing of glyphosate application because of the nonuniform level of crop maturity in the field and/or uncontrollable environmental effects.

Quantifying pesticide-contaminated sediment sources in tropical coastal environments (Galion Bay, French West Indies)

PurposeOver the last 60 years, intensification of soil cultivation led to an acceleration of soil erosion and sediment delivery to river systems. In Martinique, this acceleration has led to the remobilization of a toxic insecticide (i.e. chlordecone) used in the 1970s-1990s to control banana weevil. A previous study attributed this accelerated remobilization to the application of glyphosate in plantations from the 1990s onwards. To further unambiguously confirm this link, the identification of soil erosion sources supplied to coastal sediment is essential.MethodsAccordingly, sediment fingerprinting tools were adapted and applied to a coastal sediment core collected in the Galion Bay. Potential source samples (n=37) were collected across the drainage area. Along with the coastal sediment core layers, these samples were analysed for potential tracing properties. The optimal suite of tracers was then selected and introduced into an un-mixing model to quantify their contributions to coastal sediment.ResultsResults showed that subsoil (i.e. soil layer <30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$< 30$$\\end{document} cm depth) and banana plantation soil surface supply the major sources of sediment (49-78% and 12-36%, respectively) to the Galion Bay and that their contributions increased since 2000, in line with chlordecone and glyphosate fluxes.ConclusionThis evolution may be attributed to the higher sensitivity of banana plantations to erosion that may have been enhanced by the glyphosate application leaving the soil uncovered with vegetation and to the contamination of both topsoil and deep soil layers (<30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$< 30$$\\end{document} cm) layers with chlordecone due to its vertical transfer along the soil profile and its redistribution across hillslopes.

Cultivo de soja em área de arroz irrigado para reduzir a infestação de plantas daninhas

ABSTRACT Lowland rice in Santa Catarina (SC), Brazil, is grown as a sole crop, which has aggravated problems with weeds. In this context, the objective of this study was to evaluate the efficacy of weed management systems in soybean crops to decrease weed infestation in lowland rice production areas, using pre- and post-emergence herbicides. The experiment was conducted in Turvo, SC, from August 2021 to April 2022. A randomized block design with four replications was used, in a 6 × 5 factorial arrangement. The factors consisted of six pre-emergence herbicides treatments (S-metolachlor, diclosulam, sulfentrazone, sulfentrazone + diuron, pyroxasulfone + flumioxazin, and a control without herbicide), and five post-emergence herbicide treatments: control without herbicide, glyphosate at two rates (930 and 1,550 g a.e. ha-1), applied alone or in combination with clethodim. The herbicide sulfentrazone caused persistent phytotoxicity and resulted in the lowest soybean grain yield. The herbicide S-metolachlor was ineffective in controlling weed species, except barnyard grass, even when combined with post-emergence application. The poor control of these weed species does not result in significant interference, causing no significant decreases in grain yield of soybean crops grown in floodplain soils. The use of S-metolachlor, diclosulam, and pyroxasulfone + flumioxazin, combined with post-emergence application of glyphosate (930 g a.e. ha-1), resulted in highly effective control of barnyard grass, inhibiting weed seed production. Only the combination of glyphosate (1,550 g a.e. ha-1) with clethodim can suppress barnyard grass seed production without using pre-emergence herbicides.

Short occupational exposure to glyphosate and its biomonitoring via urinary levels of glyphosate and metabolite AMPA (Amino-MethylPhosphonic acid), in Italian vineyard workers

Glyphosate, an herbicide largely used in various contexts, can have adverse effects on human health. Although it is currently the most applied pesticide worldwide, few studies evaluated the extent of human exposure via biomonitoring. To expand such information, biological monitoring of exposure to glyphosate was conducted.The study has a before-and-after design to demonstrate the immediate impact of short-term interventions. Accordingly, the urine concentrations of glyphosate and its main biodegradation product (amino-methylphosphonic acid- AMPA) were measured before and the day after the single herbicide application in 17 male winegrowers. Urine samples were analyzed by high performance liquid chromatography coupled with a triple quadrupole mass spectrometer equipped with an electrospray ionization source.Glyphosate and AMPA were not detectable in pre-application urine samples (limit of quantification for glyphosate (LOQG) was 0.1 μg/L; limit of quantification for AMPA (LOQAMPA) was 0.5 μg/L). After application, glyphosate urinary levels were above LOQG in all workers. The median, min, and max values were 2.30, 0.51, and 47.2 μg/L, respectively. The same values were found for 50 %, 5 % and 95 % percentiles. After assigning numerical values, such as one half the LOQ, to each of the non-detects, the “z” of Wilcoxon matched-pairs signed-ranks test was −3.62 (p = 0.0003), suggesting the pre-application values being significantly lower than the post-application urinary glyphosate concentration. A similar analysis was not feasible with AMPA urinary levels, which were detectable only in 3 workers, after application. 12 (71 %) workers were significantly exposed to glyphosate, but adherence to the adoption of personal protective equipment was good: 14 (82 %) workers used gloves, 13 (76 %) used overalls and 13 (76 %) facial masks.Our data show that glyphosate can be absorbed by the workers after a single application and confirms the usefulness of biomonitoring in exposed workers. Further studies are needed in larger working populations and with multiple glyphosate applications, as well as to evaluate the correlations of glyphosate urine levels with exposure questionnaire data, in order to assess the actual relevance of risk and protection factors.

Persistence and pathway of glyphosate degradation in the coastal wetland soil of central Delaware

Glyphosate is a globally dominant herbicide. Here, we studied the degradation and microbial response to glyphosate application in a wetland soil in central Delaware for controlling invasive species (Phragmites australis). We applied a two-step solid-phase extraction method using molecularly imprinted polymers designed for the separation and enrichment of glyphosate and aminomethylphosphonic acid (AMPA) from soils before their analysis by ultra-high-performance liquid chromatography (UHPLC) and Q Exactive Orbitrap mass spectrometry methods. Our results showed that approximately 90 % of glyphosate degraded over 100 d after application, with AMPA being a minor (<10 %) product. Analysis of glyphosate-specific microbial genes to identify microbial response and function revealed that the expression of the phnJ gene, which codes C-P lyase enzyme, was consistently dominant over the gox gene, which codes glyphosate oxidoreductase enzyme, after glyphosate application. Both gene and concentration data independently suggested that C-P bond cleavage—which forms sarcosine or glycine—was the dominant degradation pathway. This is significant because AMPA, a more toxic product, is reported to be the preferred pathway of glyphosate degradation in other soil and natural environments. The degradation through a safer pathway is encouraging for minimizing the detrimental impacts of glyphosate on the environment.

Suppression of reed canarygrass by assisted succession: A sixteen‐year restoration experiment

Abstract Assisted succession could enable long‐term restoration where successional trajectories stall due to competition from invasive plants. Many invasives are shade‐intolerant; therefore, interventions reducing light availability should suppress invasion and re‐establish successional processes. However, given how ubiquitous nonlinearities are in ecology, restoration success also depends on identifying critical system thresholds, for example invader abundances below which regeneration of desired species is possible. We report the successful use of assisted succession to restore a swamp forest invaded by Phalaris arundinacea (reed canarygrass; hereafter Phalaris), initiated by a high‐density planting of woody species to outcompete Phalaris by reducing light availability. We established five pre‐planting treatments in a Phalaris near‐monoculture in Wisconsin, USA: herbicide‐only, herbicide+plough, herbicide+burn, mow+herbicide and control. In 2003 we planted 22 tree and shrub species at high densities, then in 2019 we censused the site to: (1) screen for long‐term differences among treatments, (2) evaluate long‐term effects of our interventions on community composition and (3) characterize the critical thresholds that enable invader suppression and restoration success. Vegetation responses and light availability across our four pre‐planting invader removal treatments did not differ. Late fall glyphosate application suppressed Phalaris long enough that a dense canopy of native woody species could establish and eventually out‐shade it. Overstory tree and shrub densities of 0.071/m2 suppressed Phalaris to 50% cover, but, due to nonlinearities, much higher densities were needed to reduce light availability and thus Phalaris cover enough to shift the system from being invader‐dominated. Compositional similarities between juvenile woody species and the overstory suggest a long‐term restoration success. Synthesis and applications. Invasive species management and the restoration of target plant communities can be aided by assisting successional trajectories that have stalled. We document a restoration strategy for forests invaded by shade‐intolerant invaders that is both effective and economical, as only a simple site preparation and single planting effort is required. Establishing a dense canopy of woody species in this way can break the feedbacks maintaining invader dominance and re‐introduce feedbacks enabling long‐term ecosystem recovery. We also illustrate the value of identifying critical thresholds influencing the abundance and impact of key invasive species.

Residential proximity to agricultural pesticide use and cardiovascular disease risk factors among adult Latina women in California's Salinas Valley.

Cardiovascular disease is a leading cause of death worldwide. There is limited evidence that exposure to current-use pesticides may contribute to cardiovascular disease risk. We examined the association between residential proximity to the application of agricultural pesticides and cardiovascular risk factors among 484 adult women in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study, a cohort based in an agricultural region of California. Outcome assessment was completed between 2010 and 2013. Using participant residential addresses and California's Pesticide Use Reporting database, we estimated agricultural pesticide use within one km of residences during the 2-year period preceding outcome assessment. We used Bayesian Hierarchical Modeling to evaluate associations between exposure to 14 agricultural pesticides and continuous measures of waist circumference, body mass index, and blood pressure. Each 10-fold increase in paraquat application around homes was associated with increased diastolic blood pressure (β=2.60 mm Hg, 95% Credible Interval (CrI): 0.27-4.89) and each 10-fold increase in glyphosate application was associated with increased pulse pressure (β=2.26 mm Hg, 95% CrI: 0.09-4.41). No meaningful associations were observed for the other pesticides examined. Our results suggest that paraquat and glyphosate pesticides may affect cardiovascular disease development in women with chronic environmental exposure.

Effect of soil drainage on Peruvian watergrass biochemical response and control by glyphosate

AbstractPeruvian watergrass (Luziola peruviana J.F. Gmel.) is a perennial weed often found in paddy fields in the southern region of Brazil. Its chemical control is performed mainly by herbicides such as glyphosate in burndown, whose efficacy depends on soil moisture. Under excess‐water soil conditions, glyphosate efficacy is reduced, probably due to reduced translocation and the involvement of photoassimilates partition. Furthermore, little is known about the stress tolerance of these plants subjected to water deficit. Based on that, we performed experiments to verify the effect of soil moisture on the biochemical parameters of Peruvian watergrass and glyphosate translocation to the stolon and roots. Total soluble sugars, sucrose, starch, and glyphosate concentrations in leaves, culms, roots, and glyphosate partitioning were quantified. The malondialdehyde content and the lipid peroxidation increased with the drainage. Under drainage conditions, superoxide production was higher in roots than leaves, while peroxide production was lower in roots than leaves. The electrolyte leakage increased with the drainage and glyphosate application. The total soluble sugar content varied in each organ with a significant increase in the culm 14 days after application in the draining treatment. Sucrose varied considerably and reached its maximum concentration at 21 days after herbicide application. The starch accumulation in the culm was 7 days after applying the highest glyphosate dose. The presence of glyphosate in the roots subjected to soil drainage indicates the movement of this herbicide. In conclusion, soil drainage profoundly impacts Peruvian watergrass physiology, increasing the photoassimilates and glyphosate translocation to the stolon and root. This explains why glyphosate efficacy is higher under drainage conditions.

Glyphosate contamination of drinking water and the occurrence of oxidative stress: Exposure assessment to rural Brazilian populations

Studies reported that continuous application of glyphosate can cause disturbance in aquatic/terrestrial environments. As such, the objective of this study is to discuss the risk of exposure to the herbicide in drinking water and to assess the oxidative stress in the consumers rural populations of Casimiro de Abreu/ RJ and Paraguaçu/ MG, Brazil. For this, water samples (n=69) were analysed from the home of volunteers, by FMOC derivatizing- LC-FLD method. The oxidative stress was analysed determining lipid peroxidation (MAD) and defense enzymes (SOD and CAT) in serum samples from rural population (n=42) compared to urban residents (n= 42). Results of the analysis from drinking water, despite the low and moderate risk, by the hazard quotient (HQ), revealed that the population is environmentally exposed to the glyphosate. The relevant findings showed that is important to implement monitoring/ biomonitoring programs to prevent pollution and toxic effects in the rural populations.

The effects of pre-harvest glyphosate rate and timing on yield and pre-malt quality of malting barley

The production of barley cultivars with malting and brewing quality characteristics is subject to strict grading and technical standards for the end-use market. Environmental and management factors can significantly alter grain quality, and the qualities required for malting. Crop and kernel uniformity are critical factors where variability can exceed the tolerance for meeting malt quality. A practice to address variations in crop maturity is the application of pre-harvest glyphosate. Pre-harvest glyphosate applications can, however, alter malting characteristics in barley, and, if mis-timed, can also reduce yield. A 4-year study at five locations in Alberta and Saskatchewan from 2013 to 2017 was conducted to determine the effects of pre-harvest glyphosate applications on malting barley characteristics. Glyphosate was applied at 900 and 1125 g ae ha−1 on malting barley cultivars ‘CDC Meredith’ and ‘AC Metcalfe’ malting barley at soft dough, hard dough, and physiological maturity growth stages. Yield reductions of up to 12% were observed from glyphosate applications at soft dough, and yield was maximized with applications at physiological maturity. Glyphosate application, at two rates, reduced percentage plump kernels, but did not affect kernel weight or protein concentration. The growth stage of barley plants did not provide an accurate indicator of seed moisture levels at the time of application, which motivated our conclusion that glyphosate applications can be mistimed by inaccurate indicators. The results motivate our questioning of the utility of pre-harvest glyphosate applications, given the adverse effects to barley yield and quality observed, even when applied according to the label instructions.