Translocation and degradation of pyrazosulfuron-ethyl in rice soil

BACKGROUND: Pyrazosulfuron‐ethyl {ethyl 5‐[(4,6‐dimethoxypyrimidin‐2‐ylcarbamoyl)‐sulfamoyl]‐1‐methylpyrazole‐4‐carboxylate} is a new rice herbicide belonging to the sulfonylurea group. This study reports the translocation of ¹⁴C‐pyrazosulfuron‐ethyl to rice plants and its degradation in rice‐planted and unplanted soil. RESULTS: Pyrazosulfuron‐ethyl did not show any appreciable translocation to rice shoots, as ¹⁴C‐activity translocated to the aerial portion never exceeded 1% of the initially applied ¹⁴C‐activity over a 25 day period. Results suggested that the dissipation of pyrazosulfuron‐ethyl from soils followed first‐order kinetics with a half‐life of 5.5 and 6.9 days in rice‐planted and unplanted soils respectively. HPLC analysis of the organic extract of soil samples showed the formation of three metabolites, namely ethyl 5‐(aminosulfonyl)‐1‐methyl‐1‐H‐pyrazole‐4‐carboxylate, 5‐[({[(4,6‐dimethoxy‐2 pyrimidinyl)‐amino]‐carbonyl} amino)‐sulfonyl]‐1‐methyl‐1H‐pyrazole‐4‐carboxylic acid and 2‐amino‐4,6‐dimethoxy pyrimidine, in both rice‐planted and unplanted soils. CONCLUSION: The study indicates that pyrazosulfuron‐ethyl was a short‐lived compound in the soil and was degraded relatively faster in rice‐planted soil than in unplanted soil. The herbicide did not show any appreciable translocation to rice plants. Copyright © 2011 Society of Chemical Industry     

Water and sediment dynamics of penoxsulam and molinate in paddy fields: field and lysimeter studies

BACKGROUND: In Chile, rice is cultivated under water‐seeded and continuously flooded conditions. Because herbicide dynamics in paddy fields and non‐flooded fields is different, 3 year experiments were performed to study the dissipation of molinate and penoxsulam in water and sediment. RESULTS: In field experiments, both herbicides dissipated by 45–55% from the initial applied amounts during the first 6 h after application in all crop seasons; in lysimeter experiments, dissipation amounts were approximately 10% for penoxsulam and 16% for molinate. Penoxsulam field water DT₅₀ values varied from 1.28 to 1.96 days during the three study seasons, and DT₉₀ values from 4.07 to 6.22 days. Molinate field water DT₅₀ values varied from 0.89 to 1.73 days, and DT₉₀ values from 2.82 to 5.48 days. Sediment residues were determined 2 days after herbicide application into the paddy water, and maximum concentrations were found 4–8 days after application. In sediment, DT₅₀ values varied from 20.20 to 27.66 days for penoxsulam and from 15.02 to 29.83 days for molinate. CONCLUSIONS: Results showed that penoxsulam and molinate losses under paddy conditions are dissipated rapidly from the water and then dissipate slowly from the sediment. Penoxsulam and molinate field water dissipation was facilitated by paddy water motion created by the wind. Sediment adsorption and degradation are considered to have a secondary effect on the dissipation of both herbicides in paddy fields. Copyright © 2011 Society of Chemical Industry     

Photolytic versus microbial degradation of clomazone in a flooded California rice field soil

BACKGROUND: Clomazone is a popular herbicide used on California rice fields and exhibits rapid anaerobic microbial degradation (t_1/2 = 7.9 days). To test the potential of direct and indirect photolytic degradation as a cofactor in the overall degradation rate, sacrificial time‐series microcosms were amended with water, non‐sterilized soil + water and sterilized soil + water. Clomazone was added to each microcosm, which was then exposed to natural and artificial sunlight over 35 days. Water and acetonitrile extracts were analyzed for clomazone and metabolites via LC/MS/MS. RESULTS: The calculated pseudo‐first‐order degradation rate constants (k) were k_water = 0–0.005 ± 0.003 day^?1, k_sterile = 0–0.005 ± 0.003 day^?1 and k_non?sterile = 0.010 ± 0.002–0.044 ± 0.007 day^?1, depending on light type. The formation of ring‐open clomazone, a microbial metabolite, correlated with clomazone degradation. Trace amounts of 5‐hydroxyclomazone (m/z = 256 → 125), aromatic hydroxyclomazone (m/z = 256 → 141) and an unknown product (m/z = 268 → 125) were observed. CONCLUSIONS: The photolytic degradation rate depends on both light type and the quality of the chromophores that induce indirect photolysis. Microbial degradation was found to be sensitive to temperature fluctuations. Overall, microbes are shown to be more detrimental to the environmental fate of clomazone than photolysis. Copyright © 2012 Society of Chemical Industry     

The behavior of clomazone in the soil environment

BACKGROUND: Clomazone is a herbicide used to control broadleaf weeds and grasses. Clomazone use in agriculturally important crops and forests for weed control has increased and is a potential water contaminant given its high water solubility (1100 µg mL^?1). Soil sorption is an environmental fate parameter that may limit its movement to water systems. The authors used model rice and forest soils of California to test clomazone sorption affinity, capacity, desorption, interaction with soil organic matter and behavior with black carbon. RESULTS: Sorption of clomazone to the major organic matter fraction of soil, humic acid (HA) (K_d = 29–87 L kg^?1), was greater than to whole soils (K_d = 2.3–11 L kg^?1). Increased isotherm non‐linearity was observed for the whole soils (N = 0.831–0.893) when compared with the humic acids (N = 0.954–0.999). Desorption isotherm results showed hysteresis, which was greatest at the lowest solution concentration of 0.067 µg mL^?1 for all whole soils and HA extracts. Aliphatic carbon content appeared to contribute to increased isotherm linearity. CONCLUSION: The results indicate that clomazone does not sorb appreciably to sandy or clay soils. Its sorption affinity and capacity is greater in humic acid, and consequently clomazone has difficulty desorbing from soil organic matter. Sorption appears to follow processes explained by the dual‐mode model, the presence of fire residues (black carbon) and a recently proposed sorption mechanism. Copyright © 2009 Society of Chemical Industry     

Involvement of cytochrome P‐450 enzyme activity in the selectivity and safening action of pyrazosulfuron‐ethyl

To investigate the selectivity and safening action of the sulfonylurea herbicide pyrazosulfuron‐ethyl (PSE), pyrazosulfuron‐ethyl O‐demethylase (PSEOD) activity involving oxidative metabolism by cytochrome P‐450 was studied in rice (Oryza sativa L cv Nipponbare) and Cyperus serotinus Rottb. Cytochrome P‐450‐dependent activity was demonstrated by the use of the inducers 1,8‐naphthalic anhydride and ethanol, the herbicides PSE, bensulfuron‐methyl, dimepiperate and dymron, or the inhibitor piperonyl butoxide (PBO). Growth inhibition in C serotinus seedlings was more severe than that in rice seedlings. O‐Dealkylation activities of PSE were induced differently in rice and in C serotinus, with distinctly higher activity in rice seedlings. The induced PSEOD activities were slightly inhibited by PBO in rice seedlings, whereas they were strongly inhibited in C serotinus seedlings. Dimepiperate and dymron were effective safeners of rice against PSE treatment. Treatments with herbicide alone resulted in less induction of PSEOD activity compared with combined treatments of the herbicide and safener. PSEOD activity in rice seedlings induced with herbicide alone was strongly inhibited by PBO, whereas it was weakly inhibited in rice seedlings induced with combinations of PSE and two safeners. These results suggest that O‐demethylation by cytochrome P‐450 enzymes may be involved in the metabolism of PSE and may contribute to its selectivity and safening action. Furthermore, these results suggest the existence of a multiple form of cytochrome P‐450 in plants. © 2001 Society of Chemical Industry     

Comparative acute toxicity of neonicotinoid and pyrethroid insecticides to non‐target crayfish (Procambarus clarkii) associated with rice–crayfish crop rotations

BACKGROUND: Most insecticides used to control rice water weevil (Lissorhoptrus oryzophilus Kuscel) infestations are pyrethroids. However, pyrethroids are highly toxic to non‐target crayfish associated with rice–crayfish crop rotations. One solution to the near‐exclusive reliance on pyrethroids in a rice–crayfish pest management program is to incorporate neonicotinoid insecticides, which are insect specific and effective against weevils but not extremely toxic to crayfish. This study aimed to take the first step to assess neonicotinoids as alternatives to pyrethroids in rice–crayfish crop rotations by measuring the acute toxicities of three candidate neonicotinoid insecticides, clothianidin, dinotefuran and thiamethoxam, to juvenile Procambarus clarkii (Girard) crayfish and comparing them with the acute toxicities of two currently used pyrethroid insecticides, lambda‐cyhalothrin and etofenprox. RESULTS: Neonicotinoid insecticides are at least 2–3 orders of magnitude less acutely toxic (96 h LC₅₀) than pyrethroids to juvenile Procambarid crayfish: lambda‐cyhalothrin (0.16 µg AI L^?1) = etofenprox (0.29 µg AI L^?1) ? clothianidin (59 µg AI L^?1) > thiamethoxam (967 µg AI L^?1) > dinotefuran (2032 µg AI L^?1). CONCLUSION: Neonicotinoid insecticides appear to be much less hazardous alternatives to pyrethroids in rice–crayfish crop rotations. Further field‐level neonicotinoid acute and chronic toxicity testing with crayfish is needed. Copyright © 2009 Society of Chemical Industry     

Potential of barnyard grass to remediate arsenic‐contaminated soil

The present study investigated the arsenic (As) remediation potential of barnyard grass (Echinochloa crus‐galli L. Beauv. var. formosensis Ohwi), with a special focus on the behavior of As in the soil in comparison with rice (Oryza sativa L. cv. Nipponbare). For both plants, very little growth inhibition was observed in the As‐contaminated soil. The amount of As in the soil was reduced by the plant's uptake and the level of As in the soil water from the rice‐growing pots was remarkably lower than that in the plant‐free soil water. In the soil with the barnyard grass, the amount of As in the soil water was higher than that in the plant‐free soil water, but the amount of As in the soil and the amount of As that was adsorbed on the soil solid were reduced by the plant's uptake. At the highest As level in the soil (100 mg kg^?1), 249.60 and 101.26 µg As pot^?1 were taken up by the rice shoot and barnyard grass shoot, respectively, and total amounts of 1468.65 and 1060.57 µg As pot^?1 were taken up by the barnyard grass and rice seedlings, respectively. At the same As level in the soil, the As concentrations were 14.99 and 37.76 µg g^?1 in the shoot of barnyard grass and rice, respectively, and 486.61 and 339.32 µg g^?1 in the root of barnyard grass and rice, respectively. Barnyard grass took up more As than rice, but the As concentration in the shoot of barnyard grass was lower than that in the shoot of rice. A considerable amount of As was taken up by both barnyard grass and rice, suggesting that the plant species have the potential to remediate As‐contaminated soil.     

Inheritance of resistance to fenoxaprop‐p‐ethyl in sprangletop (Leptochloa chinensis L. Nees)

Sprangletop (Leptochloa chinensis L. Nees) is a serious grass weed in direct‐seeded rice cropping systems in Thailand. One population of sprangletop, BLC1, was found to be resistant to fenoxaprop‐p‐ethyl at 62‐fold the concentration of a susceptible biotype, SLC1. This study elucidated the inheritance of resistance to fenoxaprop‐p‐ethyl in this sprangletop BLC1 genotype. The reaction to the herbicide at 0.12–2.4 mg ai L^?1 was determined in the seedlings of self‐pollinated resistant BLC1, susceptible SLC1 and SLC1 that had been allowed to cross‐pollinate with BLC1. At 0.24 mg ai L^?1, all the seedlings of SLC1 were killed, while 99% of BLC1 survived, along with 5% of the cross‐pollinated SLC1 seedlings, which were considered to be putative F₁ hybrids. The root and shoot lengths of the F₁ hybrids in 0.24 mg ai L^?1 of fenoxaprop‐p‐ethyl, relative to those in the absence of the herbicide, were close to or the same as the resistant parent, indicating that the resistance is a nearly complete to complete dominant trait. One‐hundred‐and‐forty‐one of the F₂‐derived F₃ families were classified by their response to the herbicide at 0.24 and 0.48 mg ai L^?1 into 39 homozygous susceptible : 72 segregating : 30 homozygous resistant, fitted with a 1:2:1 ratio at χ² = 1.21 and P = 0.56, indicating that the resistance to fenoxaprop‐p‐ethyl in the sprangletop BLC1 genotype is controlled by a single gene.     

Effect of long‐term field application of pendimethalin: enhanced degradation in soil

The effect of long‐term application of pendimethalin in a maize–wheat rotation on herbicide persistence was investigated. Pendimethalin was applied at 1.5 kg AI ha⁻¹ separately as one or two annual applications for five consecutive years in the same plots. Residues of pendimethalin were determined by gas chromatography. Harvest‐time residues of the herbicide decreased gradually over the years and at the end of five years less than 3% of applied pendimethalin was recovered from soil as against 18% in the first year. Residues were found distributed in the soil profile up to 90 cm depth at the end of the experiment with peak distribution of 0.03 µg g⁻¹ in the surface layer of soil treated with 10 herbicide applications. The minimum distribution was, however, in the deepest soil (75–90 cm) profile. Some of the metabolites of pendimethalin ie dealkylated pendimethalin derivative, partially reduced derivative and cyclized product were also traced in surface and sub‐surface soils up to 90 cm. A study of the rate of degradation of pendimethalin in field‐treated soils under laboratory conditions revealed faster degradation compared to control soils. Only the surface soil (0–15 cm) showed this enhanced degradation of the herbicide, which could be due to the adaptability of the aerobic micro‐organisms to degrade pendimethalin. Microbes capable of degrading herbicide were isolated, identified and pendimethalin degradation was confirmed in nutrient broth. © 2000 Society of Chemical Industry     

Dissipation of tralkoxydim herbicide from wheat crop and soil under sub-tropical conditions

The persistence of tralkoxydim herbicide in wheat crop and in soil was evaluated under Indian sub-tropical field conditions at two application rates (400 g a.i ha ^?1 and 800 g a.i ha ^?1). At 400 g a.i ha ^?1, tralkoxydim persisted up to 28 days in soil but became non-detectable only after 45 days in the crop. However, at 800 g a.i ha ^?1, tralkoxydim residues persisted for 45 days in both soil and crop. The dissipation of the herbicide from both soil and crop appeared to occur in two phases at both rates of application. Each phase followed first-order kinetics. The values of DT₅₀ and DT₉₀ for both soil and crop are reported.     

Acute toxicity of chlorantraniliprole to non‐target crayfish (Procambarus clarkii) associated with rice–crayfish cropping systems

BACKGROUND: Chlorantraniliprole, a novel anthranilic diamide insecticide, was recently introduced into the United States where rice–crayfish crop rotations are practiced to control rice water weevil (Lissorhoptrus oryzophilus Kuschel) infestations. Chlorantraniliprole has high margins of mammalian safety and excellent insecticidal efficacy, but its toxicity to non‐target crayfish is uncertain. In this study, the acute toxicity of chlorantraniliprole to the red swamp crayfish Procambarus clarkii Girard was determined using aquatic and feeding assays. RESULTS: The aquatic 96 h median lethal toxicity (LC₅₀) data indicate that technical‐grade chlorantraniliprole is highly toxic (US EPA category) to crayfish with an LC₅₀ of 951 µg L^?1 (95% CL = 741–1118 µg L^?1). A no observed effect concentration (NOEC) of 480 µg L^?1 was recorded. Neither the 36 day chronic feeding study, where crayfish fed on chlorantraniliprole‐treated rice seed in aquaria, nor the 144 h acute feeding test, where crayfish fed on rice seeds treated with chlorantraniliprole, produced mortality or abnormal behavior. CONCLUSION: Chlorantraniliprole is three orders of magnitude less acutely toxic to P. clarkii than lambda‐cyhalothrin and etofenprox, two pyrethroid insecticides also used in rice, and is less likely to cause acute crayfish toxicity in rice pond ecosystems. Based on acute toxicity data, the use of chlorantraniliprole should be more compatible with rice–crayfish crop rotations than pyrethroids. Copyright © 2010 Society of Chemical Industry     

Residues of the herbicide fenoxaprop‐P‐ethyl,its agronomic safener isoxadifen‐ethyl and their metabolites in rice after field application

BACKGROUND: Fenoxaprop‐P‐ethyl is a herbicide used on cereals and in particular on rice, the degradation of which leads to several relevant metabolites. The herbicide is used together with an agronomic safener such as isoxadifen‐ethyl, which also generates some metabolites. The present work was aimed at developing and validating an analytical method for the determination of the above parent compounds and their main metabolites in the edible fractions of rice. Parent compounds were extracted in acetonitrile and determined by gas chromatography with a mass spectrometer detector, while metabolites were extracted in acetonitrile and analysed by liquid chromatography tandem mass spectrometry. RESULTS: The method was validated through recovery tests in rice straw, grain and plant: accuracy was in the range 76–86% and 90–103% for parent compounds and metabolites respectively. Precision, as relative standard deviation, was in the range 3–11% and 6–17% for parent compounds and metabolites respectively. The limit of detection was 0.01 mg kg^?1 for each analyte, while the limit of quantification was set at 0.05 mg kg^?1. CONCLUSION: The analytical method is suitable for quantitative determination of each analyte considered in rice commodities. Copyright © 2010 Society of Chemical Industry     

Dissipation of 4-chloro-2-methylphenoxyacetic acid (MCPA) in a rice field

The dissipation of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in a California rice field was investigated. Samples of water, rice plants and mud were collected at intervals for 20 days and analysed for MCPA by established methods for plants and mud, and by a novel method utilising XAD-2 macro-reticular resin for water. Water residues declined to less than 0.01 parts/10⁶ of MCPA within 14 days after application; plant residues declined from 20 parts/10⁶ to 1 part/10⁶ within 20 days; mud residues remained constant at about 0.1 parts/10⁶. Photolysis of dilute aqueous MCPA solutions with either sunlight or an indoor photoreactor yielded 4-chloro-2-methylphenol as the major product; o-cresol and 4-chloro-2-formylphenol also were identified. While photosensitisation was observed with water taken from the rice field, microbial degradation proceeded at an even faster rate. All environmental compartments except air contained measurable amounts (>0.01 parts/10⁶) at some time, but water contained the bulk of the applied MCPA whose eventual disappearance was shown to be due to biological and chemical degradation and not dilution.     

Degradation and adsorption of 14C-MCPA in soil—influence of concentration, temperature and moisture content on degradation

MCPA was weakly absorbed in soils with 2.4, 3.0 and 2.9% humus. K_d-values were 0.7, 0.9 and 1.0, respectively. In soil, not previously treated with MCPA, the degradation of 0.05 mg kg^?114C-MCPA followed first-order reaction kinetics whereas degradation of 5 mg kg^?1 was only first-order for 2 weeks; exponentially increasing degradation rates followed indicating enrichment of the soil with MCPA decomposers. Degradation was monitored by evolution of ¹⁴CO₂. The influence of temperature on degradation of MCPA (4 mg kg^?1) could initially be described by Q₁₀ values or by the Arrhenius equation. After 1 day of incubation in two field soils Q₁₀ values were 3.3 and 2.9, respectively, between 0°C and 29°C; the activation energies were 87 and 76 kj mol^?1. Exponentially increasing degradation rates followed with doubling times of about 4.0, 1.8, 1.2 and 0.6 days at 6,10, 15 and 21°C, respectively. After 51 days of incubation, at temperatures between 6°C and 29°C, about 60%¹⁴C was evolved in CO₂ and only traces of MCPA were left in the soil. At 0°C and at 40°C only 1% and 10%¹⁴C, respectively, were evolved as CO₂ after 51 days. ¹⁴C-MCPA (4 mg kg^?1) was incubated at moisture contents from that in air-dried soil to 2.3 times field capacity. Optimum for degradation was from 0.6 to 1.2. field capacity. Degradation was very slow where water contents were below the level of wilting point and was nil in air-dried soil. In wet soil degradation was delayed, but even in water-logged soil (2.3 times field capacity) MCPA was decomposed after 4 to 5 weeks at 10°C.     

Modelling the effects of herbicide dose and weed density on rice‐weed competition

The effects of herbicide dose on rice‐weed competition were investigated to develop a combined model, which can be utilised to estimate an optimum herbicide dose for a given weed density in paddy rice cultivation. Field studies were conducted in Suwon for rice‐Echinochloa crus‐galli competition and Iksan for rice‐Eleocharis kuroguwai during 2007. The competitive effect of the weeds E. crus‐galli and E. kuroguwai decreased with increasing doses of flucetosulfuron and azimsulfuron, respectively, in the same manner as the standard dose–response curve. The combination of the rectangular hyperbolic model and the standard dose–response curve adequately described the complex effects of herbicide dose and weed competition on rice yield. Parameter estimates were used with the model to predict rice yield and estimate the doses of flucetosulfuron and azimsulfuron required to restrict rice yield loss caused by E. crus‐galli and E. kuroguwai, respectively, to an acceptable level. For a rice yield of 5.0 t ha^?1, the model recommended flucetosulfuron doses of 8.7, 13.4 and 20.1 g a.i. ha^?1 when infested with E. crus‐galli at 12, 24 and 48 plants m^?2 respectively. For a rice yield of 5.2 t ha^?1, the model recommended azimsulfuron doses of 3.9, 7.5 and 12.6 g a.i. ha^?1 when infested with E. kuroguwai at 24, 48 and 96 plants m^?2 respectively. The theoretical outputs of the combined model appear robust and indicate there are opportunities for reduced herbicide use in the field. These now require evaluation under field conditions.     

Aerobic soil metabolism of metsulfuron-methyl

A laboratory study was conducted to determine the degradation rates and identify major metabolites of the herbicide metsulfuron-methyl in sterile and non-sterile aerobic soils in the dark at 20°C. Both [phenyl-U-¹⁴C]- and [triazine-2-¹⁴C]metsulfuron-methyl were used. The soil was treated with [¹⁴C]metsulfuron-methyl (0.1 mg kg⁻¹) and incubated in flow-through systems for one year. The degradation rate constants, DT₅₀, and DT₉₀ were obtained based on the first-order and biphasic models. The DT₅₀ (time required for 50% of applied chemical to degrade) for metsulfuron-methyl, estimated using a biphasic model, was approximately 10 days (9–11 days, 95% confidence limits) in the non-sterile soil and 20 days (12–32 days, 95% confidence limits) in the sterile soil. One-year cumulative carbon dioxide accounted for approximately 48% and 23% of the applied radioactivity in the [phenyl-U-¹⁴C] and [triazine-2-¹⁴C]metsulfuron-methyl systems, respectively. Seven metabolites were identified by HPLC or LC/MS with synthetic standards. The degradation pathways included O-demethylation, cleavage of the sulfonylurea bridge, and triazine ring opening. The triazine ring-opened products were methyl 2-[[[[[[[(acetylamino)carbohyl]amino]carbonyl]amino] carbonyl]-amino]sulfonyl]benzoate in the sterile soil and methyl 2-[[[[[amino[(aminocarbonyl)imino]methyl] amino]carbonyl]amino]sulfonyl]benzoate in the non-sterile soil, indicating that different pathways were operable. © 1999 Society of Chemical Industry     

Partitioning of etofenprox under simulated California rice‐growing conditions

BACKGROUND: The pyrethroid insecticide etofenprox is of current interest to rice farmers in the Sacramento Valley owing to its effectiveness against the rice water weevil, Lissorhoptrus oryzophilus Kuschel. This study aimed to describe the partitioning of etofenprox under simulated rice field conditions by determining its Henry's law constant (H) (an estimate of volatilization) and organic carbon‐normalized soil–water distribution coefficient (K_oc) at representative field temperatures. A comparison of etofenprox and λ‐cyhalothrin is presented using a level‐1 fugacity model. RESULTS: Experimental determination of H revealed that etofenprox partitioned onto the apparatus walls and did not significantly volatilize; the maximum value of H was estimated to be 6.81 × 10^?1 Pa m³ mol^?1 at 25 °C, based on its air and water method detection limits. Calculated values for H ranged from 5.6 × 10^?3 Pa m³ mol^?1 at 5 °C to 2.9 × 10^?1 Pa m³ mol^?1 at 40 °C, based on estimated solubility and vapor pressure values at various temperatures. Log K_oc values (at 25 °C) were experimentally determined to be 6.0 and 6.4 for Princeton and Richvale rice field soils, respectively, and were very similar to the values for other pyrethroids. Finally, temperature appears to have little influence on etofenprox sorption, as the log K_oc for the Princeton soil at 35 °C was 6.1. CONCLUSION: High sorption coefficients and relatively insignificant desorption and volatilization of etofenprox suggest that its insolubility drives it to partition from water by sorbing to soils with high affinity. Offsite movement is unlikely unless transported in a bound state on suspended sediments. Copyright © 2009 Society of Chemical Industry     

Herbicidal and biological characteristics of a new benzenesulfonylurea compound K-11451 under submerged paddy conditions

The new benzenesulfonylurea K-11451, an α-hydroxy-β-fluoropropyl- compound, applied at 3–9 g ha ⁻¹, controlled annual and perennial weeds grown in submerged paddy soil under greenhouse conditions. It effectively controlled barnyardgrass at growth stages varying from pre-emergence to the five-leaf stage. The compound inhibited acetolactate synthase, I₅₀ values for the enzyme isolated from barnyardgrass and rice being 56 and 67 nM , respectively. K-11451 inhibited the growth of rice when it was transplanted at a shallow depth (0–1 cm) and water leaching from the paddy soil was high (3–5 cm per day). With a water depth of 3 cm, the compound appeared to move readily down into the paddy soil and had the relatively short half-life of 15.2 days under submerged paddy conditions. A mixture of K-11451 + mefenecet + daimuron (9 + 250 + 250 g ha⁻¹) controlled almost all weeds in the paddy field without injury to rice, so that the combination could be used as a ‘one-shot’ herbicide in rice culture.     

Systemic effects of thiamethoxam and chlorantraniliprole seed treatments on adult Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) in rice

BACKGROUND: Feeding assays using adult rice water weevils and foliage of plants treated as seeds with chlorantraniliprole and thiamethoxam at different rates were conducted to evaluate the systemic adulticidal and feeding effects. Dose–mortality relationships were determined for thiamethoxam seed treatments by combining leaf area lost due to feeding and insecticide residues analyzed by LC/MS/MS. Changes in adulticidal activity of thiamethoxam were also investigated by contrasting adult mortalities at the 5–6‐leaf and tillering stages of rice. RESULTS: Adult weevil mortalities and leaf consumption rates on foliage were affected in thiamethoxam but not in chlorantraniliprole treatments when rice was at the 6–7‐leaf stage. The LD₅₀ for weevils feeding on thiamethoxam‐treated rice at the 2–3‐leaf stage was 447 pg insecticide weevil^?1 (95% CL: 25–830 pg weevil^?1) but was lower (142 pg weevil^?1; 95% CL: 102–180 pg weevil^?1) in experiments with 3–4‐leaf‐stage plants. Mortalities on leaves from 5–6‐leaf‐stage plants were consistently higher than on leaves from tillering plants. Thiamethoxam residues measured by ELISA increased with seed treatment rate and differed between plant stages. CONCLUSION: The LD₅₀ values developed in this study are the first values for leaf‐feeding insects on foliage of plants treated as seeds with thiamethoxam. The attrition of adulticidal activity of thiamethoxam in foliage of older plants may help to explain the reduced effectiveness of seed treatments against rice water larvae that is seen at later stages of rice growth in field studies. The differential activity of these two seed treatments on adults suggests that adult mortality contributes to the field efficacy of thiamethoxam but not to that of chlorantraniliprole. Copyright © 2012 Society of Chemical Industry