Identification of a target‐site mutation conferring resistance to triazine herbicides in oriental mustard (Sisymbrium orientale L.) from Australia

In southern Australia, oriental mustard (Sisymbrium orientale) has been controlled successfully by triazine herbicides for several decades. The screening of 40 populations that were collected from the southern grain belt of Australia during 2010 and 2013 for resistance to six different herbicides (glyphosate, diflufenican, imazamox, chlorsulfuron, atrazine and 2,4‐dichlorophenoxyacetic acid) identified two oriental mustard populations as highly resistant to atrazine. Compared to the known oriental mustard‐susceptible populations (S1 and S2), these two resistant populations (P17 and P18) from near Horsham, Victoria, Australia, were 311‐ and 315‐fold resistant to atrazine, as determined by a comparison of the LD₅₀ values. However, there was no resistance to diuron detected in these populations. Sequencing of the chloroplast psbA gene identified a missense mutation of serine 264 to glycine in both herbicide‐resistant oriental mustard populations, which is known to confer high‐level atrazine resistance in other species.     

羧甲基壳聚糖/改性膨润土复合载体对莠去津释放和淋溶的影响

首次尝试将羧甲基壳聚糖与改性膨润土复合用作除草剂莠去津的载体,制备得到控释型颗粒剂,以延缓莠去津的释放,减少淋溶损失,提高药效及控制其污染。通过水中释放实验研究了制剂配方对莠去津释放速率的影响,并借助半经验方程探讨了其释放机理,采用土壤薄层实验考察了复合载体对降低莠去津淋溶的效果。 结果表明,采用复合载体时莠去津的半数释放时间(t 50)可达700 h 以上,比对照采用单一羧甲基壳聚糖作载体时延长了1倍以上。莠去津由颗粒剂向水相释放的过程主要受费克扩散(Fickian diffusion)控制,且经9次淋洗后莠去津的累计淋出率仅为6.0%,表明该复合载体控释制剂可显著减少莠去津对地下水的污染。     

Controlled release of isoproturon from an alginate–bentonite formulation: water release kinetics and soil mobility

The herbicide isoproturon [3‐(4‐isopropylphenyl)‐1,1‐dimethylurea] was incorporated in alginate‐based granules to obtain controlled‐release (CR) properties. The basic formulation (sodium alginate (1.87%)–isoproturon (0.67%) in water) was modified by addition of different sorbents. The effect on isoproturon release rate, modified by the incorporation of natural and acid‐treated bentonite in alginate formulation, was studied by immersion of the granules in water while shaking. The release of isoproturon was diffusion‐controlled. The time taken for 50% of the active ingredient to be released into water, T₅₀, was longer for those formulations containing added bentonite (5.98 and 7.43 days, for natural and acid‐treated (1 M H₂SO₄) bentonite, respectively) than for the preparation without bentonite (3.78 days). The mobilities of non‐formulated technical grade (98%) and formulated isoproturon were compared using soil columns. The use of alginate‐based CR formulations containing bentonite reduced isoproturon movement compared with the technical product. Sorption capacity of the soil for isoproturon was measured using batch experiments (0.29 litre kg⁻¹) and the results obtained here in agreement with those obtained under dynamic conditions. © 2000 Society of Chemical Industry     

Multiple herbicide‐resistant Lolium rigidum (annual ryegrass) now dominates across the Western Australian grain belt

Lolium rigidum (annual or rigid ryegrass) is a widespread annual weed in cropping systems of southern Australia, and herbicide resistance in L. rigidum is a common problem in this region. In 2010, a random survey was conducted across the grain belt of Western Australia to determine the frequency of herbicide‐resistant L. rigidum populations and to compare this with the results of previous surveys in 1998 and 2003. During the survey, 466 cropping fields were visited, with a total of 362 L. rigidum populations collected. Screening of these populations with the herbicides commonly used for control of L. rigidum revealed that resistance to the ACCase‐ and ALS‐inhibiting herbicides was common, with 96% of populations having plants resistant to the ACCase herbicide diclofop‐methyl and 98% having plants resistant to the ALS herbicide sulfometuron. Resistance to another ACCase herbicide, clethodim, is increasing, with 65% of populations now containing resistant plants. Resistance to other herbicide modes of action was significantly lower, with 27% of populations containing plants with resistance to the pre‐emergent herbicide trifluralin, and glyphosate, atrazine and paraquat providing good control of most of the populations screened in this survey. Ninety five per cent of L. rigidum populations contained plants with resistance to at least two herbicide modes of action. These results demonstrate that resistance levels have increased dramatically for the ACCase‐ and ALS‐inhibiting herbicides since the last survey in 2003 (>95% vs. 70–90%); therefore, the use of a wide range of integrated weed management options are required to sustain these cropping systems in the future.     

Release of atrazine and alachlor from clay-oxamide controlled-release formulations

Controlled-release herbicide formulations have been shown to decrease the leaching potential of several herbicides under laboratory and field conditions. The utility and efficacy of these formulations may be improved by combining several herbicides and a fertilizer source in a single formulation. The objective of these studies was to develop granular alginate formulations that were composed of a combination of the herbicides atrazine and alachlor with the slow-release nitrogen source oxamide (ethanediamide). Controlled release of the herbicides was obtained by addition of selected minerals, including calcium bentonite, fine-grind bentonite, montmorillonite K10, kaolinite and iron (III) oxide. A formulation without clay was used as a comparison. The formulations tested had herbicide active ingredient contents ranging from ∽0·02 to 0·54% and a nitrogen content of 21%. Release of the herbicides was studied by equilibrating the formulations with deionized water on a rotary shaker at 200 rev min^-1 and sampling at regular time intervals up to 104 hours. The minerals used in the different formulations influenced the herbicide active ingredient composition, as well as the release properties of the individual formulations. The atrazine content of the formulations decreased in the order calcium bentonite>fine-grind bentonite>kaolinite>montmorillonite=iron oxide>no clay. For alachlor the content decreased in the order of calcium bentonite>fine-grind bentonite>montmorillonite>iron oxide>kaolinite>no clay. Controlled release of atrazine (i.e. reduction in release rate) varied in the order calcium bentonite>iron oxide>montmorillonite>fine-grind bentonite= kaolinite>no clay, and for alachlor fine-grind bentonite>calcium bentonite>montmorillonite>no clay=kaolinite=iron oxide. A certain percentage of the applied active ingredient of both alachlor and atrazine was not recovered. From 5 to 27% of the active ingredient was not released, with the greatest retention by the bentonite formulations. Release of nitrogen was not strongly influenced by mineral type, although a trend indicated greater release with formulations containing kaolinite. © 1998 SCI     

Assessment of Chemical and Manual Weed Control Approaches for Effective Weed Suppression and Maize Productivity Enhancement Under Maize-Wheat Cropping System

Effective weed management in maize-wheat (M-W) cropping systems are accountable for higher yield and plant biomass. The objective of this study was to evaluate the effectiveness of manual weeding and chemicals (pre- and post-emergence herbicide) for actual weed control to enhance maize yield and M?W system productivity. Herbicides were treated as pre-emergence (sole), post-emergence (sole) and its combined application (pre- and post-emergence) for weed eradication and suppression. Sole pre-emergence herbicide (acetyclour?+?atrazine) and sole post-emergence herbicides (nicosulfuron), and its mixed application were used in the experiments. The experiment was comprised on 6 treatments with one weedy check or control plot: W1?=?weedy check, W2?=?acetyclour?+?atrazine, W3?=?atrazine, W4?=?nicosulfuron, W5?=?nicosulfuron?+?atrazine, W6?=?acetyclour?+?atrazine?+?nicosulfuron and W7?=?manual weeding. Main weeds were Cyperus rotundus, Tribulus terrestris, Dactyloctenium aegyptium and Cynodon dactylon. Experiential findings revealed that manual weeding was found most effective in terms of controlling weed and suppression. Among the herbicides application, promising results in terms of weed destruction and suppression were shown by combined application of acetyclour?+?atrazine?+?nicosulfuron which effectively controlled weeds as compared to other treatments. It was concluded that manual weeding drastically reduced weeds frequency and biomass while among the herbicides application acetyclour?+?atrazine and nicosulfuron could be promising for weeds suppression and clamp downing as compared to all other treatments under M?W cropping system.

     

Removal of paraquat and atrazine from water by montmorillonite‐(Ce or Zr) phosphate cross‐linked compounds

The adsorption of paraquat (1,1′‐dimethyl‐4,4′‐bipyridilium dichloride) and atrazine (6‐chloro‐N ²‐ethyl‐N ⁴‐isopropyl‐1,3,5‐triazine‐2,4‐diamine) from aqueous solution onto two montmorillonite‐(Ce or Zr) phosphate cross‐linked compounds at different temperatures (288 K and 308 K) has been studied using batch experiments. The adsorption isotherms obtained for paraquat on both adsorbents may be classified as H‐type of the Giles classification, which suggests that paraquat molecules are strongly adsorbed on the samples. For the adsorption of atrazine, L‐type isotherms were obtained for both montmorillonite‐(Ce or Zr) phosphate compounds, which suggests that these compounds have a medium affinity for this herbicide. The increase in temperature from 288 K to 308 K did not have any clear effect on the adsorption process of paraquat on either adsorbent whereas atrazine adsorption decreased slightly as temperature increased, possibly due to a mainly physical process. Fourier transform infrared (FTIR) spectroscopic studies revealed that at the pH generated by the adsorbents, the cationic herbicide interacted to a greater extent with the negatively charged surface of the adsorbents than did atrazine. For both herbicides, the Ce‐montmorillonite adsorbent showed a higher adsorption capacity than the Zr‐montmorillonite adsorbent. © 2000 Society of Chemical Industry     

Effects of soil moisture content on the availability of soil-applied herbicides to plants

The phytotoxicities of atrazine, simazine, linuron, lenacil and aziprotryne were increased as the moisture content of the soil increased. Results from studies with ¹⁴C-labelled atrazine suggested that these differences could be related to differences in concentrations of herbicide accumulated by the plants. Total uptake of atrazine was directly proportional to water uptake, but a comparison of the amounts taken up with those supplied by mass-flow in the transpiration stream suggested that some exclusion factor was operative. It was concluded that herbicide transport within the soil-plant system was the main factor affecting phytotoxicity under the different soil moisture regimes. The significance of the results to herbicide behaviour under field conditions is discussed.     

Joint action of Cochliobolus lunatus and atrazine on Echinochloa crus-galli (L.) Beauv.

The potential of the endemic fungus Cochliobolus lunatus as a biological control agent against Echinochloa crus-galli was investigated. Under appropriate conditions the fungus produced leaf necrosis on E. crus-galli resulting in death of young seedlings. However, plants with more than two leaves mostly recovered after some time. Bean, barley, maize, oat, rye, tomato and wheat were highly resistant to the fungus. In experiments in a climate room or in a glasshouse E. crus-galli with more than two leaves could effectively be controlled by C. lunatus in combination with a sub-lethal dosage of atrazine as low as 2.5 mg m^?2 due to a positive interaction between fungus and herbicide.     

A new molecular method for the rapid detection of a metamitron‐resistant target site in Chenopodium album

BACKGROUND: Resistance to photosystem II inhibitors—triazines (atrazine) and triazinones (metamitron, metribuzin)—in Chenopodium album L. is caused by the serine 264 to glycine mutation in the D1 protein. This mutation has been detected in C. album collections from Belgium with unsatisfactory metamitron efficacy in the field and was confirmed in greenhouse resistance bioassays. Incomplete herbicide efficacy in practice can also be caused by reduced uptake due to environmental conditions. Hence, for reliable differentiation and resistance identification, a rapid method for mutation detection in the target gene psbA is required. RESULTS: Dose–response curves obtained in herbicide greenhouse assays with metamitron‐resistant and ‐susceptible reference biotypes showed that a dose of 2 L ha^?1 metamitron was suitable for discrimination. A psbA PCR‐RFLP was developed, based on the presence of a FspBI restriction enzyme recognition site, covering D1 codon 264 in susceptible genotypes. A paper‐based DNA extraction allowed direct processing of leaf samples already in the field. In order to detect the mutation even in mixed seed samples, a nested PCR‐RFLP was also developed. CONCLUSION: The method allows exhaustive surveys screening C. album leaf or seed samples for the occurrence of the D1 Ser264Gly mutation to confirm or disprove metamitron resistance in the case of unsatisfactory control. Copyright © 2010 Society of Chemical Industry     

Responses of Abutilon theophrasti to agricultural management systems

Seeds of Abutilon theophrasti Medic., collected from plants growing in a continuous maize or soyabean field subjected to herbicide application, cultivation or no weed management for 10 years, differed significantly in their weight and germinability. The differences in mean weight and germinability of the progeny seeds were maintained when the parent plants were grown in a greenhouse under controlled conditions. The offspring of plants with or without previous exposure to atrazine responded similarly to the herbicide in all the measurements of the growth and development of the plants, except blooms. Significant differences between the two groups of plants were mainly observed in the weight and germinability of their seeds. Although plants with or without previous exposure to atrazine usually did not differ significantly in their response to the herbicide in terms of individual traits, they differed both in the amount and pattern of overall response across all traits. The difference in overall response between plants increased with increasing rate of atrazine. It is possible that previous exposure to the herbicide had caused minor variation in a group of inter-correlated traits or in the strength or pattern of correlation among traits.     

Conservation tillage systems for sorghum production under semi‐arid conditions in India

Abstract

Field research was conducted near Hyderabad, India, during 1981 and 1982 to investigate zero‐tillage and reduced‐tillage systems for production of sorghum (Sorghum bicolor (L.) Moench.) under semi‐arid tropical conditions. Part of the investigation compared post‐seeding hand weeding and herbicide treatments for weed control efficacy. The results showed that shallow pre‐seeding tillage was just as effective as deep cultivations in producing high sorghum fodder and grain yields provided weeds were controlled after crop emergence. Both tillage regimes were more effective than a no tillage regime which received only a mixture of glyphosate and 2,4‐D prior to seeding. Post‐seeding weed control practices were essential to maintain high fodder and grain yields of sorghum. Hand weeding and inter‐row blade harrowing were more effective than atrazine applied pre‐emergence or 2,4‐D applied post‐emergence.     

Reduced metribuzin pollution with phosphatidylcholine-clay formulations

BACKGROUND: Metribuzin is a widely used herbicide that has been identified as a groundwater contaminant. In this study, slow‐release formulations of metribuzin were designed by encapsulating the active ingredient in phosphatidylcholine (PC) vesicles and adsorbing the vesicles onto montmorillonite. RESULTS: The maximum active ingredient content in the slow‐release formulations was 246 g kg^?1. Infrared spectroscopy results revealed that the hydrophobic interactions between metribuzin and the alkyl chains on PC were necessary for encapsulation. In addition, water bridges connecting the herbicide and the PC headgroup enhanced the solubility of metribuzin in PC. Adsorption experiments in soils were performed to evaluate the relationship between sorption and leaching. Funnel experiments in a sandy soil revealed that the herbicide was not irreversibly retained in the formulation matrix. In soil column experiments, PC–clay formulations enhanced herbicide accumulation and biological activity in the top soil layer relative to a commercial formulation. PC–clay formulations also reduced the dissipation of metribuzin by a factor of 1.6–2.5. CONCLUSIONS: A reduction in the recommended dose of metribuzin can be achieved by employing PC–clay formulations, which reduces the environmental risk associated with herbicide applications. Moreover, PC and montmorillonite are non‐toxic and do not negatively affect the environment. Copyright © 2010 Society of Chemical Industry     

Availability of atrazine to plants in different soils

The concentrations of atrazine in the shoots of wheat plants growing in 12 different soils were directly proportional to the soil solution concentrations of herbicide estimated from slurry adsorption measurements. There was a marked discrepancy between the total uptake of herbicide and the amount theoretically supplied by mass-flow in response to transpiration. This discrepancy was less when plants were grown in nutrient solutions. In an experiment with one soil only, the half-life of atrazine was 22 days and when the solution concentration in this soil was corrected for this change, a much closer prediction of atrazine uptake could be obtained. The ways in which interactions between adsorption, breakdown and transpiration rates may affect herbicide toxicity under field conditions are discussed.     

Improved chemical control of Conyza bonariensis in wheat limits problems in the following fallow

Conyza bonariensis is a major weed infesting zero‐tilled cropping systems in subtropical Australia, particularly in wheat and winter fallows. Uncontrolled C. bonariensis survives to become a problem weed in the following crops or fallows. As no herbicide has been registered for C. bonariensis in wheat, the effectiveness of 11 herbicides, currently registered for other broad‐leaved weeds in wheat, was evaluated in two pot and two field experiments. As previous research showed that the age of C. bonariensis, and to a lesser extent, the soil moisture at spraying affected herbicide efficacy, these factors also were investigated. The efficacy of the majority of herbicide treatments was reduced when large rosettes (5–15 cm diameter) were treated, compared with small rosettes (<5 cm diameter). However, for the majority of herbicide treatments, the soil moisture did not affect the herbicide efficacy in the pot experiments. In the field, a delay in herbicide treatment of 2 weeks reduced the herbicide efficacy consistently across herbicide treatments, which was related to weed age but not to soil moisture differences. Across all the experiments, four herbicides controlled C. bonariensis in wheat consistently (83–100%): 2,4‐D; aminopyralid + fluroxypyr; picloram + MCPA + metsulfuron; and picloram + high rates of 2,4‐D. Thus, this problem weed can be effectively and consistently controlled in wheat, particularly when small rosettes are treated, and therefore C. bonariensis will have a less adverse impact on the following fallow or crop.     

背负式静电喷雾器静电喷施对2种玉米田除草剂的减量效应

为了明确背负式静电喷雾器静电喷施对玉米田除草剂的减量效应,以土壤处理除草剂40%乙·莠SE和茎叶处理除草剂30%苯唑草酮SC+90%莠去津WG+专用助剂作为参试除草剂,测定了背负式静电喷雾器在不同施药剂量下的静电喷施效果。结果表明:背负式静电喷雾器静电喷施对40%乙·莠SE和30%苯唑草酮SC+90%莠去津WG+专用助剂均有明显的减量效应。当40%乙·莠SE和30%苯唑草酮SC+90%莠去津WG+专用助剂中90%莠去津WG的施用量分别降至2 850 mL/hm 2和825 g/hm 2时,较各自推荐施用量分别减少用药量36.67%和21.43%,对玉米田主要杂草仍有理想的控制效果,株防效超过64%,鲜重防效超过95%;并可最大限度地改善玉米茎、穗部性状,减轻对玉米产量的影响,较人工除草分别减产1.96%和0.29%。可见,背负式静电喷雾器在玉米田土壤处理除草剂和茎叶处理除草剂喷施中具有较大的应用价值。     

Resistance of barnyardgrass (Echinochloa crus-galli) to atrazine and quinclorac

Two populations of Echinochloa crus-galli (R and I) exhibited resistance to quinclorac. Another population (X) exhibited resistance to quinclorac and atrazine. The R and I populations were collected from monocultures of rice in southern Spain. The X population was collected from maize fields subjected to the application of atrazine over several years. The susceptible (S) population of the same genus was collected from locations which had never been treated with herbicides. The quinclorac ED₅₀ value (dose causing 50% reduction in shoot fresh weight) for the R and I biotypes were 26- and 6-fold greater than for the S biotype. The X biotype was 10 times more tolerant to quinclorac than the S biotype and also showed cross-resistance to atrazine, being 82-fold more resistant to atrazine than the R, I and S biotypes. Chlorophyll fluorescence and Hill reaction analysis supported the view that the mechanism of resistance to atrazine in the X biotype was modification of the target site, the DI protein. Quinclorac at 20 mg litre^-1 did not inhibit photosynthetic electron transport in any of the test biotypes. The quinclorac I₅₀ values (herbicide dose needed for 50% Hill reaction reduction) of the S population was over 50000-fold higher than the atrazine I₅₀ value for the same S population, indicating that quinclorac is not a PS II inhibiting herbicide. Propanil at doses greater than 0·5 kg ha^-1 controlled all the biotypes. © 1997 SCI     

Microbial aspects of atrazine biodegradation in relation to history of soil treatment

Among 15 soils with different cropping practices, seven which had an history of repeated atrazine applications showed accelerated degradation of this herbicide. By contrast, grassland or agricultural soils with no recorded atrazine application, at least for the last three years, had a low degradation potential. No direct relation was found between the rate of atrazine mineralisation and the size of the microbial biomass. In adapted soils, the amounts of extractable residues were lowered and the very high percentages of radioactivity from [ring-¹⁴C]atrazine recovered as [¹⁴C]carbon dioxide demonstrated that N-dealkylation and deamidation were the only processes for micro-organisms to derive carbon and energy for heterotrophic growth. Kinetics of microbial ¹⁴C accumulation revealed that atrazine ring carbon could be incorporated by direct oxidative condensation with structural components of the bacterial or fungal cell whereas side-chain carbon was preferentially used for biosynthesis of new protoplasmic cell material, as confirmed by the high turnover rate of radiolabelled microbial components. From the determination of the Michaelis–Menten parameters, V_m and K_m in the presence of different selective biocides, it was possible to conclude that fungi were probably less active in atrazine degradation than bacteria and that over years the microbial atrazine-degrading community showed an increased efficiency. © 1999 Society of Chemical Industry     

Herbicide‐resistant weeds in the Philippines: Status and resistance mechanisms

Two major weeds in rice in the Philippines, Sphenochlea zeylanica Gaertn. and Echinochloa crus‐galli (L.) Beauv., are controlled with chemical and cultural methods. In the 1980s, after >10 years of continuous use of 2,4‐D, S. zeylanica evolved resistance to the chemical in those rice fields that had been treated with 2,4‐D once or twice every cropping season. In the 1990s, E. crus‐galli evolved resistance to butachlor and propanil in rice monocrop areas where both herbicides were used continuously for 7–9 years. Rice farmers continue to use 2,4‐D, butachlor and propanil extensively and are often unaware of herbicide resistance or the potential for cross‐resistance, its causes or its implications. In order to control herbicide‐resistant E. crus‐galli, farmers are shifting to locally available herbicides with different modes of action, such as bispyribac, an acetolactate synthase inhibitor, and cyhalofop, an acetyl coenzyme A carboxylase inhibitor. Follow‐up manual weeding or rotary weeding after herbicide spraying, a common farmers’ practice, removes the susceptible and resistant biotypes and could help to delay or prevent the evolution of resistance. Although the resistance mechanisms of both weeds are not determined yet, they could be related to enhanced degradation that is similar to the mechanisms that are shown by the resistant biotypes in other countries.     

Resistance of Amaranthus hybridus to atrazine

Resistance of weeds to triazine herbicides has been recorded in many countries. The extent of the problem in South Africa is uncertain. In a pilot study, the atrazine resistance of Amaranthus hybridus L. (smooth pigweed) was investigated. Suspected resistant (R) and susceptible (S) biotypes were treated with commercially formulated atrazine. After post-and pre-emergence applications under tunnel conditions, it was found that the suspected R biotype plants were not affected at herbicide dosages of belween 1.25 and 25.0 kg a.i. ha^-1, i.e. up to 20 times gieater than the lowest recommended dosage. However, the S biotype plants were killed by the lowest dosage. In the fieid, mortalities in the R biolype were not observed after post-emergence applications of 1.25-10.00 kg a.i. ha^-1. In contrast, all S biotype plants were killed. In tunnel experiments, the R biotype was also found to be resistant to cyanazine and cyanazine+atrazine, while slight tolerance to linuron was observed. All these treatments resulted in 100% mortality of the S biotype. Although S biotype seeds oi A. hybridus were found to germinate slightly sooner under controlled conditions than R biotype seeds, preliminary results suggest that there are no major differences. Indications are that, although the growth of the S biotype may be greater than that of the R biotype, the competitive effect of the two biotypes on crop seedlings may well be similar.