Perennial Grass Weeds Research Articles

Understanding the responses of tillering to 2,4-D isooctyl ester in Setaria viridis L.

BackgroundGreen foxtail [Setaria viridis (L.)] is one of the most abundant and troublesome annual grass weeds in alfalfa fields in Northeast China. Synthetic auxin herbicide is widely used in agriculture, while how auxin herbicide affects tillering on perennial grass weeds is still unclear. A greenhouse experiment was conducted to examine the effects of auxin herbicide 2,4-D on green foxtail growth, especially on tillers.ResultsIn the study, 2,4-D isooctyl ester was used. There was an inhibition of plant height and fresh weight on green foxtail after application. The photosynthetic rate of the leaves was dramatically reduced and there was an accumulation of malondialdehyde (MDA) content. Moreover, applying 2,4-D isooctyl ester significantly reduced the tillering buds at rates between 2100 and 8400 ga. i. /ha. Transcriptome results showed that applying 2,4-D isooctyl ester on leaves affected the phytohormone signal transduction pathways in plant tillers. Among them, there were significant effects on auxin, cytokinin, abscisic acid (ABA), gibberellin (GA), and brassinosteroid signaling. Indeed, external ABA and GA on leaves also limited tillering in green foxtail.ConclusionsThese data will be helpful to further understand the responses of green foxtail to 2, 4-D isooctyl ester, which may provide a unique perspective for the development and identification of new target compounds that are effective against this weed species.

Evaluation of organic options for Johnsongrass (Sorghum halepense) control during winter fallow

AbstractJohnsongrass [Sorghum halepense (L.) Pers.] is one of the most problematic perennial grass weed species in row-crop production across the southern United States. Control of this species is especially challenging in organic systems due to a lack of effective options. A field experiment was conducted at the Texas A&M research farm near College Station, TX, from fall 2019 to spring 2021 to evaluate various nonchemical options for managing S. halepense in the fallow season, implemented over 2 yr in the same locations. The treatments included disking once, disking twice, disking + immediate flooding, disking + flush irrigation + flooding, disking twice + flooding after the first frost, periodic mowing, acetic acid treatment, and disking + tarping. Disking + immediate flooding, disking + flush irrigation + flooding, and disking + tarping were the most effective treatments. Compared with the nontreated control plots, these treatments reduced S. halepense aboveground density (<9 plants m−2 vs. 64 plants m−2), aboveground biomass (<80 g m−2 vs. 935 g m−2), rhizome biomass (<4 g m−2 vs. 55 g m−2), rhizome node number (<25 nodes m−2 vs. 316 nodes m−2), and rhizome length (<42 cm m−2 vs. 660 cm m−2). Disking twice + flooding after the first frost did not show a consistent impact. Periodic mowing also reduced S. halepense density (12 plants m−2 vs. 64 plants m−2) and other variables compared with the control plots at the end of the study in spring 2021. Disking alone once or twice each growing season or repeated application of acetic acid failed to control S. halepense. These results indicate that well-timed nonchemical management practices such as tarping and flooding implemented during the winter fallow can be very effective in reducing S. halepense densities.

Drought tolerance in tough lovegrass (Eragrostis plana): Understanding mechanisms and competitive ability

AbstractEragrostis plana Nees is a perennial grass weed, native to South Africa and an invasive species of dry rangelands across Asia, Australia, and South America. We hypothesise that E. plana has evolved mechanisms of acclimation to drought conditions to a greater extent than bahiagrass (Paspalum notatum), an important native grass forage species of livestock rangelands of Brazil, leading to a competitive advantage. We measured morphological, physiological, and biochemical response traits in E. plana and P. notatum to water deficit and competition. Levels of drought tolerance in the two species were greatest at the tillering growth stage, driven by low levels of leaf relative water content in E. plana and early stomatal regulation to avoid water loss in P. notatum. The mechanisms used to dissipate energy excess under drought are associated with an efficient antioxidant system and the biosynthesis of compatible osmolytes (proline). Despite reductions in fitness, both species survived a series of drought cycles, where E. plana showed a competitive advantage over P. notatum. These results help to explain the invasion success of E. plana in rangelands and demonstrate its potential threat to native biodiversity, particularly under drought conditions.

Tumble windmill grass (Chloris verticillata Nutt.) control with POST herbicides

AbstractTumble windmill grass (Chloris verticillata Nutt.) is a problematic perennial grass weed in the semiarid Central Great Plains (CGP). Greenhouse and fallow field experiments were conducted during 2021 and 2022 at Kansas State University Agricultural Research Center near Hays, KS, to determine the effectiveness of various POST herbicides for tumble windmill grass control. All selected POST herbicides were applied at field‐recommended rates at the seedling growth stage (3‐to 4‐inches tall) of tumble windmill grass in greenhouse study. Tumble windmill grass was at the heading growth stage (10‐to‐12‐inches tall) in fallow fields when POST herbicides were tested. Results from greenhouse study indicated that quizalofop‐P‐ethyl (QPE) and clethodim provided ≥ 95% control and shoot biomass reduction of tumble windmill grass at 28 days after treatment. Glyphosate provided 89% control and 93% shoot biomass reduction of tumble windmill grass. Imazamox and nicosulfuron had the least control (41 to 51%) and shoot biomass reduction (43 to 66%) of tumble windmill grass in greenhouse study. In contrast, all tested POST herbicides were comparatively less effective on tumble windmill grass (≤68% control and ≤ 50% shoot biomass reduction) except glyphosate (85% control and 54% shoot biomass reduction) in field study. These results conclude that clethodim, QPE, and glyphosate applied at early growth stages can provide effective control of tumble windmill grass in the CGP region.

Development of immunoassay based on a specific antibody for sensitive detection of nicosulfuron in environment

Nicosulfuron, one of the most widely used selective herbicides in corn field, can effectively control annual and perennial grass weeds, sedges, and some broadleaf weeds. The residual phytotoxicity of nicosulfuron in soil and water has become increasingly prominent. Therefore, an efficient method for detection of nicosulfuron was critical to ensure the sustainable and healthy development of agriculture and the ecological environment. In this paper, five nicosulfuron haptens which contained carboxyl group or aldehyde groups were designed and synthesized, and an indirect competitive immunoassay was developed for the first time. The assay showed an IC50 of 8.42 ng/mL and had negligible cross reactivities toward other sulfonylurea herbicides. In the spike and recovery studies, the recovery rate from soil samples was 95 %–104 %, and that of wheat roots was 92 %–98 %, which showed a good correlation with LC-MS analysis for nicosulfuron. The immunoassay was then used to quantify nicosulfuron concentration which could cause the obvious phytotoxic symptoms to wheat. Obvious symptoms of nicosulfuron phytotoxicity in wheat root was observed at the concentration of 0.068 ± 0.006 mg/kg (ELISA result) which was consistent with 0.072 ± 0.007 mg/kg obtained by LC-MS. The developed immunoassay method is an effective tool for environment contamination monitoring.

Identifying hair fescue in wild blueberry fields using drone images for precise application of granular herbicide

Hair fescue is a common perennial grass weed in wild blueberry fields in Nova Scotia, Canada and reduces yield if not adequately controlled. Hair fescue is typically managed with a broadcast propyzamide application which is costly for growers. Current research on the management of hair fescue in wild blueberry fields focuses on the development of a precision granular herbicide applicator with individual nozzle control. The integration of aerial images could benefit current work by providing a large-scale perspective on hair fescue location. This research suggests a new strategy to identify infield areas with hair fescue infestation, generate prescription maps, and integrate them into a widely available navigation system of heavy farming equipment to improve the processing workflow of hair fescue detection on a larger scale. This method proposes the integration of multi-resolution segmentation on multispectral (Blue, Green, Red, Red Edge, Near-Infrared) drone images to group hair fescue plants into segments with similar spectral characteristics. The best performing segmentation was classified and tested on wild blueberry fields in Nova Scotia. Results were assessed by comparing classified boundaries to reference data collected with high resolution RGB images. Findings from hair fescue and wild blueberry spectral profiles showed that hair fescue could be identified using blue, green, and red bands and showed no advantages over multispectral cameras. Results from the classification of wild blueberry and hair fescue showed high Kappa coefficient values of 0.90 and 0.94 and overall accuracy of 95 and 97% were achieved for both fields surveyed. Results also demonstrated an average potential cost saving of $CAD1246.43 ha-1 when compared to a broadcast application of granular dichlobenil. This work represents the first attempt to integrate aerial imagery and a precision granular herbicide applicator to manage important weeds in wild blueberry fields.

Evaluation of amino acid–inhibiting herbicide mixtures for hair fescue (Festuca filiformis) management in lowbush blueberry

AbstractHair fescue is a perennial grass weed in lowbush blueberry fields that forms dense sods and reduces yield. As a result of natural tolerance or resistance of this grass to other currently registered herbicides growers rely on preemergence (PRE) applications of pronamide and postemergence (POST) applications of the Group 2 herbicides foramsulfuron and nicosulfuron + rimsulfuron for hair fescue management. This causes repeated application of Group 2 herbicides, which is compounded by the recent registration of flazasulfuron for POST suppression of hair fescue in lowbush blueberry. Mixtures of Group 2 herbicides with the amino acid–inhibiting herbicides glyphosate (Group 9) and glufosinate (Group 10), however, can improve weed control and may delay herbicide resistance development. This research used a factorial arrangement of Group 2 herbicides (none, foramsulfuron [35 g ai ha−1], nicosulfuron + rimsulfuron [13 + 13 g ai ha−1], flazasulfuron [50 g ai ha−1]) and mixtures (none, with glyphosate [902 g ae ha−1], and with glufosinate [750 g ai ha−1]) to identify possible mixtures that improve weed control and delay resistance development. Herbicides were applied in spring nonbearing year, fall bearing year, and fall nonbearing year, with each application timing conducted as a separate experiment. Foramsulfuron and nicosulfuron + rimsulfuron were not effective as fall applications, and spring applications of these herbicides with glyphosate or glufosinate improved hair fescue suppression. Glyphosate and glufosinate were more effective as fall rather than spring applications. Flazasulfuron was effective across all application timings, although its mixture with glufosinate generally improved hair fescue suppression. Flazasulfuron + glufosinate is tentatively recommended as an effective mixture for management of spring nonbearing-year and fall bearing-year hair fescue in lowbush blueberry.

The amino acid substitution Phe-255-Ile in the psbA gene confers resistance to hexazinone in hair fescue (Festuca filiformis) plants from lowbush blueberry fields

AbstractCultivation of lowbush blueberry (Vaccinium angustifolium Aiton), an important crop in the eastern part of North America, is unique, as it is carried out over the course of two consecutive growing seasons. Pest management, particularly weed management, is impacted by this biennial cultural practice. The choice of methods to control weeds is narrow, and such a system relies heavily on herbicides for weed management. Availability of unique herbicide active ingredients for weed management is limited, and available herbicides are used repeatedly, so the risk of developing resistance is acute. Hair fescue (Festuca filiformis Pourr.), a perennial grass weed, has evolved resistance to hexazinone, a photosystem II inhibitor frequently used in lowbush blueberry production. We show that substitution of phenylalanine to isoleucine at position 255 is responsible for a decreased sensitivity to hexazinone by a factor of 6.12. Early diagnosis of resistance based on the detection of the mutation will alert growers to use alternative control methods and thus help to increase the sustainability of the cropping system.

Weed Survey of Nova Scotia Lowbush Blueberry (Vaccinium Angustifolium Ait.) Fields

ABSTRACT Weed surveys provide the basis for weed management research in lowbush blueberry, but have not been conducted in Nova Scotia since 2001. Documented declines in herbicide efficacy, loss and/or acquisition of herbicide active ingredients, confirmation of herbicide-resistant weed biotypes, and documented vectoring of weed seeds by machinery necessitate a new weed survey. A total of 165 bearing year lowbush blueberry fields were surveyed from 2017 to 2019, within which approximately 211 weed species were identified. Most weed species were herbaceous perennial forbs (89 species) and woody perennials (50 species), followed by annual broadleaf (24 species) and perennial grass weeds (20 species). The remaining flora consisted of a range of ferns, biennials, sedges and rushes, and orchids. The most common weed species were red sorrel (Rumex acetosella L.), poverty oatgrass (Danthonia spicata L. Beauv.), haircap moss (Polytrichum commune Hedw.), hair fescue (Festuca filiformis Pourr.), narrow-leaved goldenrod (Euthamia graminifolia (L) Nutt.), tickle grass (Agrostis hyemalis (Walter) BSP.), woolly panicum (Panicum lanugosum Ell.), cow wheat (Melampyrum lineare Desr.), bunchberry (Cornus canadensis L.), and yellow hawkweed (Hieracium caespitosum Dumort). Increased occurrence of these weed species is likely the result of documented or observed reductions in hexazinone and terbacil efficacy, confirmation of triazine-resistant biotypes, and common occurrence of seeds of these weed species on machinery. Low crop prices have also caused reduced pronamide use, contributing to increased occurrence of hair fescue. Results are guiding future research priorities for weed management in lowbush blueberry.

Evaluation of terbacil-based herbicide treatments for hair fescue (Festuca filiformis) management in lowbush blueberry

AbstractHair fescue is a common tuft-forming perennial grass weed that reduces yields and hinders mechanical harvest in lowbush blueberry fields. PRE terbacil applications traditionally controlled hair fescue but currently only provide suppression in most fields. Terbacil use has not, however, been evaluated in conjunction with other currently registered herbicides in lowbush blueberry. The objective of this research was to evaluate a range of terbacil-based herbicide treatments for hair fescue management in lowbush blueberry. The experiment was conducted at three lowbush blueberry fields in Nova Scotia, Canada. Spring nonbearing-year terbacil applications (2,000 g ai ha–1) exhibited variable efficacy on hair fescue with reduced total tuft density at one site and reduced flowering-tuft density and flowering-tuft inflorescence number at two sites. Suppression was limited to the year of application only. Terbacil followed by (fb) foramsulfuron (35 g ai ha–1) did not improve suppression. A terbacil tank mixture with glufosinate (750 ai ha–1), however, reduced flowering-tuft density and flowering-tuft inflorescence number at each site and reduced total tuft density at one site, suggesting improved suppression with terbacil + glufosinate relative to terbacil alone. Terbacil + glufosinate fb foramsulfuron gave additional reductions in total tuft density at two sites and reduced bearing-year flowering-tuft density at two sites, indicating that hair fescue suppression with this herbicide combination extends into the bearing year. Although less effective than the industry standard pronamide applications, terbacil + glufosinate or terbacil + glufosinate fb foramsulfuron could be used as part of a weed management program for hair fescue in lowbush blueberry.

Sourgrass phenological stage and efficacy of ACCase-inhibiting herbicides

Abstract Background: Sourgrass (Digitaria insularis) is a highly disseminated weed in Brazil. It is a perennial grass weed that has high infesting capacity in agricultural areas and presents glyphosate-resistant biotypes. An effective post-emergence control of sourgrass plants depends on their phenological stage at the time of herbicide application. Objective: This work was developed with the objective of evaluating the effect of the sourgrass phenological stage at the time of herbicide application on the efficacy of ACCase-inhibiting herbicides. Methods: Two independent experiments were conducted under greenhouse conditions to evaluate two ACCase-inhibiting herbicides: clethodim, and haloxyfop. The treatments were applied using a completely randomized block design, with an 8×4 factorial arrangement consisted of 8 herbicide rates (4, 2, 1, 1/2, 1/4, 1/8, and 1/16 times the recommended rate, and a control plot without herbicide application) and four phenological stages of sourgrass. Results: The development of sourgrass plants after tillering decreased the efficacy of the herbicide molecules; however, clethodim and haloxyfop were efficient to control sourgrass at earlier developmental stages. Morphological, anatomical, and physiological changes in older plants may explain the lower susceptibility to herbicides. Conclusions: Other control techniques should be considered for sourgrass plants at later developmental stages, such as sequential application or herbicide mixtures, to increase the efficacy of ACCase herbicides.

Relationships between soil, forage, and grazing parameter effects on weed incidence in Missouri pastures

AbstractDuring the 2015, 2016, and 2017 growing seasons, a survey of 63 pastures in Missouri was conducted to determine the effects of selected soil and forage parameters on the density of common annual, biennial, and perennial weed species. Permanent sampling areas were established in each pasture at a frequency of one representative 20-m2 area per 4 ha of pasture, and weed species and density in each area were determined at 14-d intervals for a period from mid-April until late September. The parameters evaluated included soil pH, phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), sulfur (S), zinc (Zn), manganese (Mn), and copper (Cu) concentrations, as well as tall fescue density, forage groundcover density, and stocking rate. An increase of 1 unit in soil pH was associated with 146 fewer weeds per hectare, the largest reduction in weed density in response to any soil parameter. Increased soil pH was associated with the greatest reduction in perennial grass weed density, along with an average reduction of 1,410 brush weeds per hectare for each 1-unit increase in soil pH. Common ragweed, a widespread weed of pastures, could be reduced by 3,056 weeds ha−1 when soil pH was 1 unit greater. A 1-ppm increase in soil P was correlated with a decrease of 206 biennial broadleaf weeds per hectare. Perennial broadleaf weed density was reduced in soils with greater concentrations of P, K, and Ca. Additionally, for every 1% increase of tall fescue and forage groundcover, there was a decrease of 18 and 38 perennial broadleaf weeds per hectare. The results from this research indicate that the density of many common weed species can be reduced with higher soil pH and adjustments to soil macro- and micronutrient concentrations, especially P.

Responses of Detoxification Enzymes and Genes to Nicosulfuron Stress in Two Genotypes of Sweet Corn Differing in Nicosulfuron Tolerance

Nicosulfuron, a sulfonylurea herbicide is registered for use on field, controns many annual and perennial grass weeds. The accumulation of nicosulfuron will increase toxicity and induce unfavorable oxidative stress in plants. Acetolactate synthase (ALS, EC 2.2.1.6) and glutathione transferases (GSTs, E. C.2.5.1.18), which participate in detoxification of xenobiotics and limit oxidative damages of cellular macromolecules, are important groups of cytoprotective enzymes. This study aims to investigate the toxic effect of nicosulfuron on the detoxification enzyme activities and gene expressions in maize seedling. Specifically, Nicosulfuron-tolerant sweet inbred line ‘JP233’ and nicosulfuron-sensitive sweet inbred line ‘Z2H4’ are subjected to 80mg kg–1 nicosulfuron treatment when the fourth leaves are fully developed, and the resulting effects are compared to those processed by water. After nicosulfuron treatment, it is found that ALS and GST enzymes activities of Z2H4 are significantly lower than those of JP233. Compared to Z2H4, nicosulfuron treatment increases the expression levels of GST1, ALS1 and ALS2 genes in JP233. These results suggest that the increased transcription level of these detoxifying enzymes might play a vital role in reducing the toxicity of nicosulfuron and the oxidative stress induced by nicosulfuron in maize seedlings. The research will improve our understanding of the function of maize detoxification enzymes and genes in herbicide metabolism.

Control of torpedograss (Panicum repens) and Southern watergrass (Luziola fluitans) in bermudagrass turf

AbstractTwo species, torpedograss and Southern watergrass, are very difficult to selectively control when they invade desirable turfgrass stands. The purpose of this study was to evaluate selective control of torpedograss and Southern watergrass in ‘Tifway’ bermudagrass turf. Greater than 86% control of torpedograss was observed 4 wk after sequential treatment (WAST) with quinclorac, trifloxysulfuron-sodium, quinclorac and trifloxysulfuron-sodium, sulfentrazone + imazethapyr and quinclorac and trifloxysulfuron-sodium, and quinclorac and trifloxysulfuron-sodium followed by (fb) glyphosate. However, by 8 WAST, control was reduced to <36% for all treatments. Greatest Southern watergrass control was achieved 4 WAST with trifloxysulfuron-sodium (83%), and thiencarbazone-methyl + foramsulfuron + halosulfuron-methyl (75%). Limited control (<30%) was observed with other treatments. By 8 WAST, Southern watergrass control was <12% for all treatments. This study suggests that short-term control/suppression of these two species is possible; however, long-term control is limited with single-year programs. These weeds will probably require multiple applications in successive years to reduce infestations. Future research should continue to screen other herbicides, combinations, and timings for control of these and other perennial grass weeds.

Evaluation of a pre-formulated post-emergence herbicide mixture of topramezone and dicamba on annual weeds and Bermuda grass in maize in a sub-tropical agro-ecology

Weed infestation is one of the major causes of low maize grain yield in sub-Saharan Africa (SSA). The perennial grass weed, Cynodon dactylon (L.) Pers., is one of the most problematic weeds in maize in SSA. A pre-formulated post-emergence herbicide mixture (50 g a.i. topramezone litre−1 + 160 g a.i. dicamba litre−1), sold under the trade name Stellar-Star®, was evaluated for C. dactylon and general weed control in the 2013/14 and 2014/15 season. The experiment was laid out as a randomized complete block design (RCBD) with six treatments replicated thrice, namely; weedy control, hoe weeding at 3 and 6 weeks after crop emergence (WACE), a label recommended dose of Stellar-Star at 3 WACE, a reduced Stellar-Star dose (75% of label dose) at 3 WACE, a double dose of Stellar-Star split applied at 3 and 6 WACE and a tank mix of label doses of Stellar-Star + Atrazine applied at 3 WACE. The Stellar-Star herbicide treatments did not significantly (P > 0.05) affect C. dactylon density at 5 WACE but significantly reduced (P < 0.001) its density at 10 WACE. The Stellar-Star herbicide treatments significantly reduced (P < 0.001) weed biomass compared to the weedy-check at 5 and 10 WACE in both seasons. The Stellar-Star double dose split application and the Stellar-Star Atrazine tank mix were most effective in controlling C.dactylon (90–97% control) followed by the Stellar-Star label dose and Stellar-Star reduced dose (75%–88% control), however, the results of this study suggest that the Stellar-Star Atrazine tank mix provided the most effective early season and overall weed control and resulted in the highest yield, rainfall use efficiency (RUE) and gross margin and is recommended.

Florpyrauxifen-benzyl activity on perennial grass weeds found in Louisiana rice production – ERRATUM

Florpyrauxifen-benzyl activity on perennial grass weeds found in Louisiana rice production – ERRATUM

Florpyrauxifen-benzyl activity on perennial grass weeds found in Louisiana rice production

AbstractA glasshouse study was conducted on the Louisiana State University campus in Baton Rouge, LA, to evaluate the control of brook crowngrass, rice cutgrass, southern watergrass, and water paspalum. Florpyrauxifen-benzyl was applied at 30 g ai ha−1 to each grass species at the 3- to 4-leaf or 1- to 2-stolon stage of growth. Brook crowngrass treated with florpyrauxifen was controlled 71% at 21 d after treatment. Southern watergrass and water paspalum control did not exceed 56% and 36%, respectively, across all evaluations. Rice cutgrass treated with florpyrauxifen did not reach 15% control. Plants treated with florpyrauxifen, except rice cutgrass, displayed reduction in leaf number, stolon number, plant height, and plant fresh weight. These results indicate florpyrauxifen-benzyl can help manage a brook crowngrass infestation and suppress southern watergrass. However, florpyrauxifen-benzyl has little to no activity on water paspalum and rice cutgrass, and other management options should be employed if these weeds are present.

The role of seedbanks in invasions by Hyparrhenia hirta (L.) Stapf in Australia

Hyparrhenia hirta (L.) Stapf (also known as Coolatai grass, South African bluestem or thatching grass) has become a serious invasive weed in Australia. Within its native range, it is generally regarded as a useful grass particularly for thatching, and seed production is low with a low soil seed bank of from 2 to 200seedsm–2. Several hundred accessions of H. hirta were deliberately introduced into Australia up until the 1980s and nearly all were discarded because of poor seed production. However, at least one introduction in the 1890s in northern New South Wales (NSW), Australia, has possibly contributed to the present serious weed problem. Annual seed production from roadside stands in northern NSW ranged from 7000 to 92000seedsm–2 in 2015. The soil seed bank under dense H. hirta infestations in the same region in 2006 and 2007, was found to be ~30000seedsm–2 mostly confined to the top 2cm, with few dormant seeds and a large reduction of these numbers over the next 12 months when further seed input was prevented. Similar studies of other perennial grass weeds have found seed banks of similar sizes, but dormancy mechanisms ensure that their seed banks last for at least 10 years without further seed input. These results suggest that the present weedy populations of H. hirta have dramatically increased fecundity enabling a large seed bank to develop beneath dense stands. The development of seed dormancy and consequently a long-lived seed bank would make this weed even more difficult to control. Until seed dormancy develops, control of H. hirta in northern NSW can be effective provided further input into the seed bank can be prevented.

Chlorination of bromacil: Kinetics and disinfection by-products

Bromacil, a nonselective uracil compound, is applied to field crops, such as citrus and pineapple, to control annual and perennial grass weeds. In this study, the degradation kinetics and effects of influencing factors on the formation of disinfection by-products (DBPs) during bromacil chlorination were investigated. The reaction between chlorine and bromacil followed second-order kinetics, and the degradation kinetic model for bromacil chlorination was established. The rate constants of the reactions between bromacil and HOCl and ClO− were calculated as 4.33 (±1.40) × 101 and 3.21 (±0.47) × 102 M−1 s−1, respectively. The presence of Br− in water resulted in the formation of HOBr and accelerated the rate of bromacil degradation during chlorination. The rate constant was calculated as 6.34 (±0.09) × 104 M−1 s−1 for the reaction between bromacil and HOBr at 25 °C. The apparent second-order rate constant (kapp) increased with increase in temperature and pH, and the activation energy was calculated as 37.83 kJ/mol using the Arrhenius equation. Because the structure of bromacil comprises bromine atoms, brominated DBPs, including dibromochloromethane (DBCM) and bromodichloromethane (BDCM), formed abundantly during bromacil chlorination. The formation of bromoform (BF), BDCM, and DBCM increased with the reaction time, whereas the formation of chloroform (CF) increased until day 4 and then decreased. The yields of all the detected DBPs increased with the increase in pH from 5 to 8. With increasing bromide concentration, the formation of CF and BDCM gradually decreased, where as that of BF considerably increased, resulting in relatively stable bromine utilization factor in the bromide to chlorine ratio of 0.00–0.10 during bromacil chlorination.

Dissipation Dynamic and Final Residues of Oxadiargyl in Paddy Fields Using High-Performance Liquid Chromatography-Tandem Mass Spectrometry Coupled with Modified QuEChERS Method.

Oxadiargyl, which binds to the protoporphyrinogen oxidase IX to exhibit herbicide activity, is mainly used in the prevention of certain perennial broadleaved and grass weeds during the preemergence of rice in paddy fields. However, oxadiargyl affects the germination and seedling growth of rice, causing damage to the plant and reducing rice yield. Hence, monitoring fate and behaviour of oxadiargyl in rice paddy fields is of great significance. A modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) sample preparation method coupled with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was established in paddy water, paddy soil, rice straw, paddy hull, and brown rice. We validated this method for the first time in the analysis of the dissipation dynamic and residues of oxadiargyl over two years (2015–2016) at three sites in China. The average recoveries of oxadiargyl ranged from 76.0 to 98.8%, with relative standard deviations of 3.5–14.0%. The dissipation curves for paddy soil fit to a first-order kinetic equation, revealing that oxadiargyl degraded rapidly in paddy soil with half-lives (t1/2) of 4.5–7.6 days. The final oxadiargyl residues in all samples remained below the detection limit and the maximum residue limit in China (0.02 mg kg−1) and Japan (0.05 mg kg−1) during the harvesting dates and were not detected in rice straw.