Differences in the molecular basis of resistance to the cyclohexanedione herbicide sethoxydim in Lolium multiflorum

Resistance to the cyclohexanedione (CHD) herbicide sethoxydim was investigated in two UK Lolium multiflorum populations, Yorks A2 and PYL. Resistance screening experiments demonstrated a qualitative difference in the responses of the two populations to sethoxydim, suggesting that the molecular basis of resistance between them was different. After treatment, Yorks A2 plants were either alive (78% of sample tested) or dead (22% tested) but plants of the PYL population showed two further intermediate categories of response. The level of acetyl-CoA carboxylase (ACCase) insensitivity directly correlated with the degree of resistance at the whole plant level, indicating that the molecular basis of resistance is associated with differences in ACCase sensitivity in each population. Direct sequencing of the carboxyl transferase domain of the ACCase gene showed that an Ile-418-Leu substitution in the L. multiflorum chloroplastic ACCase (GenBank accession number AY710293 ) confers resistance to sethoxydim in Yorks A2. This corresponds to amino acid residue 1781 in the Alopecurus myosuroides full ACCase sequence. This is the first report of this mutation in this L. multiflorum, which has also been reported in four other grass-weeds, including L. rigidum. However, no amino acid substitutions were found to be specifically associated with the resistant phenotypes in the PYL population and the molecular basis of resistance in this population remains to be resolved.     

Persistence of chlorfenvinphos in soils

The persistence and behaviour of chlorfenvinphos, an organophosphorus insecticide, was studied on different soils. On a peaty soil the insecticide was only very slowly degraded, there being 70% of the applied dose remaining after 21 weeks and 30% after nearly 12 months. On the sandy soils, however, persistence was much shorter; between 3 and 15% of the applied dose remained after a period of 15 weeks. Rates of loss appear to be related to soil moisture conditions; in dry seasons, although the initial rate of loss was high, subsequent rate of breakdown was slower than in wetter seasons. The results are discussed relative to the efficiency of the insecticide for controlling brassica root fly.     

Persistence of the herbicide AC 92,553, N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine,in soils

The effects of soil temperature and soil moisture content on the rate of loss of N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine (I, AC 92,553) were measured under controlled conditions. The time for 50% disappearance in a sandy loam soil at 75% of field capacity was inversely related to temperature (98 days at 30°; 409 days at 10°). At 25°, the half-life increased with decreasing soil moisture content (122 days at 75% of field capacity; 563 days at 12.5%). In seven soils with different properties there was a trend towards a slower rate of loss as the organic matter content of the soils increased and the half-life varied from 72 to 172 days, first-order kinetics being obeyed. The herbicide was lost rapidly from an inert surface and 97% loss was recorded after 28 days at 25°. Losses from soil surfaces occurred more slowly and were greater from wet compared with dry soil. In the field, it was more persistent when incorporated than when applied to the soil surface. More than 60% of I incorporated in April 1975 could be detected the following September, but when applied to the soil surface, only about 20% of the applied dose remained by this time. Residues measured by gasliquid chromatography using a thermionic nitrogen detector closely paralleled those measured by a bioassay based on the root growth of buckwheat.     

Toxicological studies with the 1,3,5-triazine herbicide cyanazine

Acute and long-term mammalian toxicity studies were carried out with the 1,3,5-triazine herbicide cyanazine (I) and its two major plant and soil metabolites DW 43 85 (II) and DW 4394 (III). Depending upon the species used, the acute oral LD50 values for cyanazine ranged from 140-750 mg/kg, the values in any one species not being influenced by formulation. The acute, percutaneous LD50 values were greater than 1000 mg/kg, the maximum dose which could be administered. Cyanazine was non-irritant to eyes and skin and a non-sensitiser to skin. The acute oral LD50 in rats for (II) was 789 mg/kg and for (III) was >2000 mg/kg. In 13-week studies on cyanazine, reduced growth rates and organ weight changes were the most sensitive criteria of exposure, 25 parts/million in the diet of rats and 5 mg/kg orally dosed to dogs being considered to be without toxicological effect. In two year studies 12 parts/million in the diet of rats and 1.25 mg/kg, orally dosed to dogs produced no changes of toxicological significance. In 13-week studies with (II) and (III), intakes of up to 10 000 parts/million in the diet failed to produce any toxicologically significant changes.     

A root bioassay procedure for the determination of chlorsulfuron, diclofop acid and sethoxydim residues in soils

Measurement of the root lengths of pre-ger-minated oat seedlings (Avena sativa L. var. Sioux) grown in the dark in treated soils was used to assay residues of diclofop acid (2-[4-(2,4-dichloro-phenoxy)phenoxy]propionate) and sethoxydim (2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propy]-3-hydroxy-2-cyclohexene-1-one). Similar measurements involving maize seedlings (Zea Mays L. var. Sunny Vee) were also used to determine residues of the herbicide chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbony]benzenesulfonamide) in soils. The procedure appeared to be reproducible with residues of chlorsulfuron, diclofop acid and sethoxydim being detectable at amounts of 0.001, 0.2 and 0.05 μg g^?1 respectively.     

Measurement and simulation of herbicide transport in macroporous soils

Lysimeter experiments were carried out to study pesticide transport through macroporous soils. In order to differentiate between the effects of soil structure and chemical behaviour, the leaching experiments were conducted using disturbed and undisturbed soil samples. Two herbicides with different sorption behaviours, and bromide as tracer were applied. The results were used to validate a dynamic simulation model which considers bypass flow in macropores. The simulation results show that the model is able to reproduce the soil suction within the soil as well as the spatial distribution of bromide and the herbicides. The continuity of the macropores is most important for the efficiency of bypass flow. The results indicate that cultivation practices like ploughing significantly influence the temporal and spatial distribution of the macropores. © 1998 SCI.     

Persistence and metabolism of dinitroaniline herbicides in soils

The persistence, binding, and metabolism of six dinitroaniline herbicides, including trifluralin, profluralin, dinitramine, butralin, fluchloralin, and chlornidine, added to Matapeake silt loam were determined after 3, 5, and 7 months. Dinitramine was rapidly degraded during the first 5 months, while butralin and chlornidine were less persistent than fluchloralin, profluralin, and trifluralin after 7 months. The latter three herbicides were similar in persistence and binding properties. The parent herbicide was the major extractable product detected in soil at each sampling time. Degradation products were identified by cochromatography on thin-layer plates, retention times on gas-liquid and high-pressure liquid chromatography, and mass spectral analysis. Dealkylated and cyclic derivatives of the parent herbicide were detected as metabolites. The cyclic products included benzimidazole derivatives of dinitramine, trifluralin, and fluchloralin; a morpholine derivative of chlornidine; and a quinoxaline derivative of fluchloralin. A unique metabolite of butralin was derived from the parent material by the loss of one nitro substituent.     

Persistence and mobility of bromacil in orchard soils

Bromacil was applied annually for 6 or 7 years in two apple-orchard experiments. At intervals of a year after the last applications, concentrations at various depths down to more than 1 m were measured by gas-liquid chromatography. On an average, 54% of the annual dosage was still present, corresponding to a decline to 35% of the initial amount within a year. The highest concentration in the profile was found at about 10–20 cm, which indicates a much lower mobility than that found with soil thin-layer experiments. Traces of bromacil were found at depths around 1 m, especially with the higher dosages. The upper limits of the amount leaching below a depth of 1 m were estimated at less than 3% of the dosage. Persistance et mobilité du bromacile dans les sols de vergers. Du bromacile a été apporté annuellement pendant six ou sept ans dans des essais effectués dans deux vergers de pommiers. A des intervalles d'une année aprés la derniére application, les concentrations ont été mesurées par chroma-tographie gaz-liquide, á des profondeurs variées allant jusqu'a plus d'un métre. En moyenne, il a été retrouvé 54% de la dose annuelle, ce qui correspond á une diminution de 35% de l'apport initial, dans l'intervalle d'une année. Les concentrations les plus fortes dans le profil ont été trouvées aux environs de 10 à 20 cm, ce qui indique une mobilité beaucoup plus lente que ce qui a été trouvé dans des expériences avec des couches minces. Des traces de bromacile ont été retrouvées à des profondeurs avoisinant 1 m, particuliére-ment avec des dosages élevés. Les limites supérieures du lessivage à une profondeur inférieure à 1 m ont été estimées à moins de 3% de la dose. Persistenz und Mobilität von Bromacil im Boden von Obstanlagen In zwei Apfelanlagen wurde iiber sechs bzw. sieben Jahre, jährlich einmal Bromacil angewendet. In Abständen von einem Jahr nach den letzten Anwendungen wurde das Herbizid in verschiedenen Bodentiefen bis liber 1 m Tiefe gaschromatographisch nachgewiesen. Im Durchschnitt waren noch 54% der jährlichen Aufwandmenge vorhanden. Das entspricht einer Abnahme der ursprünglich ausgebrach-ten Herbizidmenge um 35% innerhalb eines Jahres. Die höchste Konzentration wurde in einer Tiefe von etwa 10–20 cm gefunden. Die Mobilität des Herbizids war, verglichen mit seiner Beweglichkeit in Versuchen mit der Boden-Dunn-schicht-Chromatographie wesentlfch geringer. Spuren von Bromacil wurden besonders bei den hoheren Aufwand-mengen in einer Tiefe von 1 m gefunden. Es wird angenom-men, dass die hochste Herbizidmenge, die liber 1 m tief transportiert wurde, weniger als 3% der Aufwandmenge entspricht.     

The breakdown of the triazine herbicide cyanazine in soils and maize

Radioisotope techniques have been used to study the breakdown products that are formed from the herbicide cyanazine ( BLADEX )^a, 2-chloro-4-(1-cyano-1-methylethyl-amino)-6-ethylamino-1,3,5-triazine, in soils and in maize grown in the soils under indoor conditions. In soils of different types cyanazine broke down mainly by conversion of the nitrile group to amide ( II ) and then to an acid ( III ) followed by hydrolysis of the ring chlorine to hydroxyl ( IV ). Dealkylation reactions occurred to only a limited extent in soils. In maize plants grown in treated soils the hydrolysis products, the amide ( II ) and the hydroxy acid ( IV ) were detected as well as appreciable quantities of products ( VI ) and ( VIII ) formed from these by loss of the N-ethyl group. In plants the hydroxy acids ( IV ) and ( VIII ) were present in the free form and there was also evidence for conjugates which were not identified but could be converted to these hydroxy acids, ( IV ) and ( VIII ), on treatment with acids. In these indoor studies the major residues appear to be the hydroxy acid ( IV ) in soils and ( IV ) and its dealkylated analogue ( VIII ) in plants grown in treated soils. These compounds are not herbicides and are of a low order of toxicity to mammals.     

Persistence studies with [14C] 2,4-D in soils previously treated with herbicides and pesticides

The persistence of [¹⁴C] 2,4-D at a rate equivalent to 1 kg/ha was compared under laboratory conditions in samples of heavy clay, sandy loam, and clay loam at 85% of field capacity moisture and 20 ± 1°C which had either received no pre-treatment, or had been pre-treated for 7 days at the 2 μg/g level with the herbicides benzoylprop-ethyl, diclofop-methyl, dinitramine, flamprop-methyl, nitrofen, picloram, tri-allate, trifluralin, and a combination of tri-allate and trifluralin. The breakdown of [¹⁴C] 2,4-D was also studied in the same soils that had similarly received pre-treatments of 2 μg/g of the cereal seed dressing Vitaflo-DB, the insecticide, malathion, and a combination of Vitaflo-DB and malathion. In each soil type, the half-life of the 2,4-D was similar regardless of whether the soil had, or had not, received any pre-treatment, indicating that none of the chemicals investigated adversely affected the soil degradation of 2,4-D.     

The fate of the herbicide benzoylprop-ethyl in crops grown in treated soils

The herbicide benzoylprop-ethyl (SUFFIX,^a ethyl (±)-2-(N-benzoyl-3,4-dichloro-anilino) propionate) is applied post-emergence for the control of wild oats (Avena spp.) in wheat. During application some falls onto the soil and in the present work the possible uptake of residues from the soil, particularly by rotation crops has been studied using radioisotope techniques under indoor and outdoor conditions. Soil application at 1 kg/ha gave lower residues in wheat in the year of application than were found in previous studies using overall foliar-soil application. In the radiochemical experiments soil residues did persist into the following year, but residues in potatoes and wheat grown in these soils, although generally below the limit of determination (0.005 mg/kg), were occasionally just above this level (0.006 mg/kg). On the results of the present work, residues in rotational crops from soils treated in the previous year are unlikely to reach the limits of normal analytical determination.     

Microbiological degradation of the herbicide dicamba in moist soils at different temperatures

The persistence of [¹⁴C]dicamba (3,6-dichloro-2-methoxy-benzoic acid) at the 2 ppm level was studied in three prairie soils at field capacity moistures and temperatures ranging from –5±1° to 35±1°C. Following extraction of the soils with aqueous calcium chloride solution a radiochemical analytical procedure was used to monitor the breakdown. In all soils no loss of dicamba was observed at –5± 1°C, but breakdown was apparent at temperatures above 5±1°C. On a heavy clay and a silty clay an almost steady relationship between temperature and percentage degradation occurred between 5± 1° to 35± 1°C. Rate of breakdown was more rapid on the organic silty clay than on heavy clay or sandy loam. Over 80% of the [¹⁴C]dicamba was dissipated from the silty clay in 8 days at temperatures above 15±1°C, while 14 days, and temperatures in excess of 20± 1°C, were required for loss of similar amounts of the herbicide from the heavy clay and the sandy loam. Degradation biologique de l'herbicide dicamba dans les sols humides a diverses temperatures La persistance du [C¹⁴] dicamba (acide 3,6-dichloro-2-méthoxybenzoique) à la concentration de 2 ppm a étáétudiée dans trois sols de prairies à l'humidité de la capacité au champ et à des températures allant de – 5± 1°C à 35± 1° C. Aprés extraction des sols par une solution aqueuse de chlorum de calcium, un procédé analytique radiochimique a été utilisé pour suivre la dégradation. Dans tous les sols, aucune perte de dicamba n'a été observée à 5±1° C, mais la dégradation s'est produite aux températures supérieures à 5±1°C. Dans une argile lourde et dans un limon argileux, une relation presque constante est apparue, entre 5±1° et 35± 1° C, entre la température été le pourcentage de dégradation. Le taux de dégradation a été plus rapide dans un limon argileux organique dans une argile lourde ou dans les sol argilo-silicieux. Plus de 80% du [C¹⁴] dicamba a disparu dans le limon argileux, en huit jours, à des températures supérieures à 15±1° C, alors que quatorze jours et des températures supérieures à 20± 1° C ont été nécessaires pour des pertes similaires d'herbicide dans l'argile lourde et le sol argilo-silicieux. Der mikrobielle Abbau des Herbizlds Dicamba in feuchten Boden, bei unterschieldlicher Temperatur Es wurde die Persistenz von ¹⁴C-Dicamba (3,6-Dichlor-2-methoxy-benzoesaure) bei einer Konzentration von 2 ppm in drei Prärieboden bei Feldkapazitat und einem Tempera-turbereich von – 5± 1°C bis 35+1°C untersucht. Nach der Extraktion der Boden mit einer wSsserigen Lösung von Cal-ciumchlorid wurde der Abbau radiochemisch verfolgt. Bei – 5±1°C war in alien Böden keine Abnahme des Dicambagehalts festzustellen. Bei Temperaturen über 5°C war jedoch ein Abbau des Herbizids zu verzeichnen. Bei einem schweren Ton- und einem Schluff-Tonboden war bei 5± 1°C bis 35± 1°Ceine nahezu gleichmassige Beziehung zwischen Temperatur und prozentualem Abbau festzustellen. Die Abbaurate war im Schluff-Tonboden, der einen gewissen Gehalt an organischer Substanz aufwies, grosser als im schweren Tonboden oder in sandigen Lehmboden. Vom Schluff-Tonboden verschwanden mehr als 80% des ¹⁴C-Dicamba innerhalb von acht Tagen bei Temperaturen von über 15°C. Für den schweren Ton- und den sandigen Lehmboden waren hingegen 14 Tage und Temperaturen von über 20°C notig.     

Persistence and biodegradation of vinclozolin in tropical rice soils

The persistence of vinclozolin in three tropical rice soils, widely varying in their physicochemical characteristics, was compared under both non-flooded and flooded conditions. Degradation of the fungicide was more rapid in all the soils under flooded conditions than under non-flooded conditions. Kinetic analysis indicated that the degradation of the fungicide followed a first-order reaction irrespective of soil or water regime. Soil acidity and salinity significantly affected the persistence of the fungicide under non-flooded conditions. The degradation of the dicarboxymide fungicide was enhanced following repeated applications to an alluvial soil under both water regimes, with the enhancement being more marked under flooded conditions. Faster degradation of vinclozolin in mineral salts medium inoculated with non-sterile suspension from retreated alluvial soil indicates the involvement of micro-organisms. 3,5-Dichloroaniline was detected as a metabolite in the degradation of the fungicide in both soil and mineral salts medium. © 1999 Society of Chemical Industry     

The fate of the herbicide chlortoluron and its possible degradation products in soils

Chlortoluron hadàhalf-tire in soil of 4–6 weeks. The only metabolite identified was monomethyl chlortoluron, half-life 8 weeks. 3-Chloro-4-methylphenylurea hadàsimilar half-life but was not detected in soils treated with chlortoluron or monomethyl chlortoluron suggesting that 3-chloro-4-methylaniline was formed directly from monomethyl chlortoluron. This aniline hadàhalf-life of 1–2 days in soil, initial concentrations above 5 ppm yielding dimers and trimers predominantly C — N linked. Neither the aniline nor polymeric products were detected in chlortoluron treated soils, presumably because slow formation of the aniline was followed by rapid degradation which kept concentration low.     

Estimating relative crop yield loss resulting from herbicide damage using crop ground cover or rated stunting, with maize and sethoxydim as a case study

The research goal was to determine whether crop damage from herbicides measured early in the growing season soon after treatment could be used to estimate relative crop yield loss. Percentage stunting was rated visually and percentage crop ground cover (i.e. percentage of the ground surface covered by vegetation) was determined from video photographs taken 2–4 weeks after sethoxydim-susceptible maize ( Zea mays L.) was sprayed with sethoxydim at various rates plus crop oil concentrate. Averaged over 3 years, relative percentage maize yield was a negative sigmoidal function of relative sethoxydim rates from 0.065× to 0.5×, where the 1× rate was 420 g a.i. ha⁻¹ ( r ² = 0.80). Relative maize yield was positively linearly related to percentage crop ground cover and negatively linearly related to rated percentage stunting averaged over 3 years. Linear regression models of relative maize yield vs. percentage maize ground cover explained only slightly more data variability ( r ² = 0.86) than did rated stunting ( r ² = 0.82) over 3 years. The advantages and disadvantages of rated stunting and crop ground cover as scientific measurements are discussed.     

Persistence and metabolism of imidacloprid in different soils of West Bengal

A laboratory experiment was performed to study the persistence of imidacloprid from two formulations (Confidor 200 g litre-1 SL and Gaucho 700 g kg-1 WS), and its metabolism in three different soils (Gangetic alluvial soil of Kalyani, lateritic soil of Jhargram and coastal alkaline soil of Canning) of West Bengal following application at 0.5 kg and 1.0 kg AIha-1. Dissipation of imidacloprid in soil followed first-order kinetics and DT50 values ranged from 28.7 to 47.8 days. The shortest half-lives (28.7 and 35.8 days) were observed in the lateritic soil of Jhargram for both liquid and powder formulations. The formation of two metabolites of imidacloprid, imidacloprid-urea and imidacloprid-olefin, was first detected on day 30 of degradation at 28 (+/- 1) degrees C in all three soils.     

Use of corn root protoplasts in herbicide absorption studies

Intact and viable protoplasts were enzymatically isolated from corn (Zea mays L.) seedling roots and collected for herbicide absorption studies by differential centrifugation and flotation through a Ficoll density gradient. A method was developed for terminating herbicide absorption by rapid centrifugation of protoplasts out of solutions without washing the protoplasts. Within 10 sec, atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] accumulated in protoplasts to a concentration 36% greater than the external concentration; no further absorption occurred through 30 min. However, 2,4-D [2,4-dichlorophenoxyacetic acid] accumulated to twice and 16 times the external concentration at pH 6.5 and 4.5, respectively. Calculations of theoretical 2,4-D concentrations in protoplasts also predicted greater accumulation at pH 4.5 than at pH 6.5. Both atrazine and 2,4-D absorption were consistent with previous measurements of absorption by plant tissues. Thus, corn root protoplasts are feasible experimental material for studying absorption of herbicides at the cellular level.     

Persistence of gamma-BHC and beta-BHC in Indian rice soils under flooded conditions

The relative persistence of [¹⁴C]-gamma-BHC and [¹⁴C]-beta-BHC in Indian rice soils under flooded conditions was studied. In alluvial, laterite and pokkali (acid sulphate, saline) soils, rapid degradation of both isomers occurred; in sandy and kari (acid sulphate, saline) soils, both isomers persisted even after 41 days of flooding. The rapid degradation of BHC isomers in the former three soils was related to highly negative redox potentials within 20 days of flooding in contrast to oxidised conditions in sandy and kari soils even after 41 days. During the degradation in the soils, beta-BHC showed longer lag than gamma-BHC. Results suggest that the degradation of beta-BHC commences at a potential lower than that required for gamma-BHC degradation. Greater decomposition of gamma-BHC occurred in rice straw-amended soils than in unamended soils when the insecticide was incorporated to the soils in an aqueous solution. Addition of BHC isomers to the soils in ethanol resulted in comparable rates of rapid decomposition in both rice straw-amended and unamended soils, since ethanol was as effective as rice straw in lowering the redox potentials of the soils favouring BHC decomposition in unamended soil as well.     

Persistence of imazamethabenz-methyl in soils after autumn and spring applications to wheat

Imazathabenz-methyl dissipated rapidly in sandy and sandy loam field soils in Nova Scotia. Canada, seeded to wheat ( Triticum aestivam L.).The time to 50% loss of herbicide residues in the 0-10 cm soil zone was about 3-4 weeks after October applications and about 2.5 weeks after June ones. After October applications, there was further loss of >60% of the remaining parent herbicide during the winter and early spring despite periods of prolonged snow cover and freezing, or near freezing, soil temperatures. After October applications, imazamethabenz-methyl residues in May-collected samples from the 10-20 and 20-30 cm soil zones ranged from 40% to 80% and from 15% to 40%, respectively of those extracted from the 0-10 cm zone over four sites. Precipitation in the month after October applications ranged from 105 to 180 mm. which suggests leaching may play an important role in dissipation at times of the year when precipitation greatly exceeds evapotranspiration. Levels of the phytoioxic free acid ranged from 15% to 35% of the parent herbicide in selected samples. These residues had no effect on spring wheat replacement crops. The effect of the herbicide on replacement crops may also be influenced by the soil pH. A laboratory study demonstrated that as soil pH increased from 4.1 to 6.5. degradation of imazamethabenz-methyl increased with a corresponding increase in free acid formation.     

Effect of recent cropping history and herbicide use on the degradation rates of isoproturon in soils

Five soil samples were taken from each of five fields with different crop management histories. Three of the fields were in an arable rotation, the fourth field was temporary grassland, and the final field was under permanent grass. Of the three arable fields, two had been cropped with winter wheat in three of the preceding 6 years, and the third had last been cropped with winter wheat once only, 6 years previously. With one exception, the winter wheat had been sprayed with the herbicide isoproturon. The rate of isoproturon degradation in laboratory incubations was strongly related to the previous management practices. In the five soils from the field that had been treated most regularly with isoproturon in recent years, <2.5% of the initial dose remained after 14 days, indicating considerable enhancement of degradation. In the soils from the field with two applications of the herbicide in the past 6 years, residues after 27 days varied from 5% to 37% of the amount applied. In soils from the other three sites, residue levels were less variable, and were inversely related to microbial biomass. In studies with selected soils from the field that had received three applications of isoproturon in the previous 6 years, kinetics of degradation were not first‐order but were indicative of microbial adaptation, and the average time to 50% loss of the herbicide (DT₅₀) was 7.5 days. In selected soils from the field that had received just one application of isoproturon, degradation followed first‐order kinetics, indicative of cometabolism. Pre‐incubation of isoproturon in soil from the five fields led to significant enhancement of degradation only in the samples from the two fields that had a recent history of isoproturon application.