Analysis of soils for diclofop-methyl and diclofop

A method is described for the analysis of soils for residues of the herbicide diclofop-methyl, methyl (RS)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionate, and its breakdown product diclofop, (RS)-2-[4-(2,4-dichlorophenoxy)phenoxy]propionic acid. Diclofop-methyl undergoes hydrolysis in the soil to diclofop, which also has herbicidal activity. A procedure, using a 1% phosphoric acid solution for extraction purposes, has been developed and gives good recoveries of both diclofop-methyl and diclofop at the 0.5 and 0.05 mg kg^?1 levels. After methylation, gas-liquid chromatography with electron-capture detection is used to determine total residue concentrations.     

Diclofop‐resistant Lolium rigidum from northern Greece with cross‐resistance to ACCase inhibitors and multiple resistance to chlorsulfuron

Repeated use of ACCase‐ and ALS‐inhibiting herbicides in northern Greece has resulted in the evolution of a population of Lolium rigidum resistant to diclofop and chlorsulfuron. The biotype from Athos was highly resistant to diclofop and also exhibited differential cross‐resistance to clodinafop, fluazifop, tralkoxydim and sethoxydim. Assay of ACCase activity confirmed that the resistant biotype was tenfold more resistant to diclofop than the susceptible biotype, suggesting that the resistance mechanism could involve an altered target site. The diclofop‐resistant biotype has also exhibited multiple resistance to chlorsulfuron and the mechanism for this is unknown. Seed‐bioassay was found to be a rapid, cheap and reliable method to identify populations of L rigidum resistant to ACCase inhibitors and chlorsulfuron. Moreover, root elongation in the seed bioassay was more sensitive to ACCase inhibitors and chlorsulfuron than shoot elongation. © 2000 Society of Chemical Industry     

Persistence studies with the herbicide sethoxydim in prairie soils

The persistence of [¹⁴C]sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one) at the 2 μg g^?1 level was studied under laboratory conditions in three soils at 20°C and 85% of their field capacity moistures. Following extraction of the soils with methanol, the herbicide remaining was determined using radiochemical techniques. Loss of radioactivity was more rapid on moist clay loam and sandy loam, where the half-lives were 12 days, than on heavy clay in which the half-life was 26 days. Loss of radioactivity from air-dried soils (15% of field capacity) was negligible with over 94% of the applied activity being recovered after 28 days. The persistence of sethoxydim at a rate of 1 kg ha^?1 was investigated under field conditions using small plots at three prairie locations for 3 successive years. Using an oat-root bioassay procedure, no residues were detected in the 0–10 cm depths of any soils, any year, in September following May treatments.     

Comparison of physiological effects of fluazifop-butyl and sethoxydim on oat (Avena sativa L.)

Laboratory experiments were conducted to compare the physiological effects of two herbicides: fluazifop-butyl {butyl ( RS )-2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy]-propionate} and sethoxydim {(±)-2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on oat ( Avena sativa L. cv. Zenshin). The herbicides strongly inhibited growth of oat and induced chlorosis at the basal part of shoots and ethylene production from the seedlings. The phytotoxicity of these herbicides in oat seedlings was alleviated by 2,4-D (2,4-dichlorophenoxyacetic acid), but not by IAA (indole-3-acetic acid). Coleoptile elongation induced by 2,4-D or IAA was inhibited by fluazifop-butyl and sethoxydim, suggesting both herbicides possess the activity to inhibit this auxin action. Fluazifop (free acid) and sethoxydim inhibited proton excretion from oat roots but fluazifop-butyl did not. This proton excretion was not restored by 2,4-D or IAA. Furthermore, cellular electrolyte leakage in oat shoots was increased by both herbicides, indicating that the membrane permeability was increased. We conclude that fluazifop-butyl and sethoxydim may have the same mechanism of action which leads to disruption of membrane integrity, although fluazifop-butyl acts as a free acid after hydrolysis (fluazifop).     

Potential safeners for protecting sorghum (Sorghum bicolor (L.) Moench) against chlorsulfuron,fluazifop-butyl and sethoxydim*

In greenhouse studies, the efficacy of the herbicide safeners NA(1,8-naphthalic anhydride), R-25788 (N,N-diallyl-2,2-dichloroacetamide), cyometrinil and CGA-92194 [N-(1,3-dioxolan-2-yl-methoxy)imino-benzeneaceto-nitrile] in protecting grain sorghum (Sorghum bicolor (L.) Moench, cv. ‘Funk G623’) against injury from pre-emergence or early post-emergence applications of the herbicides chlorsulfuron, fluazifop-butyl and sethoxydim was examined. NA as a seed dressing at 0·5 or 1·0% (w/w) was the most effective of the four safeners and offered partial to good protection to sorghum against injury from the lower rates of pre-emergence applications of all three herbicides. R-25788 was totally ineffective as a sorghum protectant against fluazifop-butyl injury but it did antagonize partially the injurious effects of the lower rates of sethoxydim and chlorsulfuron on sorghum. Cyometrinil and CGA-92194 offered partial protection to sorghum against injury from the lowest rate of all herbicides but their efficacy against higher rates of the three herbicides was very limited. None of the four safeners was effective in protecting grain sorghum against injury from post-emergence applications of the three herbicides tested.     

Contamination of internationally traded wheat by herbicide‐resistant Lolium rigidum

As herbicide‐resistant weeds have spread in the agricultural fields of grain‐exporting countries, their seeds could be introduced into other countries as contaminants in imported grain. The spread of resistance genes through seed and pollen can cause significant economic loss. In order to assess the extent of the problem, we investigated the contamination by herbicide‐resistant annual ryegrass (Lolium rigidum) of wheat imported from Western Australia into Japan. Annual ryegrass seeds were recovered from wheat shipments and seed bioassays were conducted to identify resistance to the herbicides that are commonly used in Australia: diclofop‐methyl, sethoxydim, chlorsulfuron, and glyphosate. Nearly 4500 ryegrass seeds were detected in 20 kg of wheat that was imported in both 2006 and 2007. About 35% and 15% of the seeds were resistant to diclofop‐methyl, 5% and 6% were resistant to sethoxydim, and 56% and 60% were resistant to chlorsulfuron in 2006 and 2007, respectively. None was resistant to glyphosate in either year. As the contamination of crops by herbicide‐resistant weeds is probably a common phenomenon, the monitoring of incoming grain shipments is necessary to stem the further spread of herbicide‐resistant weeds into importing countries.     

Influence of the herbicides hexazinone and chlorsulfuron on the metabolism of isolated soybean leaf cells

The effects of the herbicides hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] and chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide) on the metabolism of enzymatically isolated leaf cells from soybean [Glycine max (L.) Merr., cv. ‘Essex’] were examined. Photosynthesis, protein, ribonucleic acid (RNA), and lipid syntheses were assayed by the incorporation of specific radioactive substrates into the isolated soybean leaf cells. These specific substrates were NaH¹⁴CO₃, [¹⁴C]leucine, [¹⁴C]uracil, and [¹⁴C]acetate, respectively. Time-course and concentration studies included incubation periods of 30, 60, and 120 min and concentrations of 0.1, 1, 10, and 100 μM of both herbicides. Photosynthesis was the most sensitive and first metabolic process inhibited by hexazinone. RNA and lipid syntheses were also inhibited significantly by hexazinone whereas the effect of this herbicide on protein synthesis was less. The most sensitive and first metabolic process inhibited by chlorsulfuron was lipid synthesis. Photosynthesis, RNA, and protein syntheses were affected significantly only by the highest concentration of this herbicide and longest exposure. Although these two herbicides may exert their herbicidal action by affecting other plant metabolic processes not examined in this study, hexazinone appears to be a strong photosynthetic inhibitor, while the herbicidal action of chlorsulfuron appeared to be related to its effects on lipid synthesis.     

Effect of chlorsulfuron on four graminicides for weed control and wheat yield

In field experiments with spring wheat (Triticum aestivum L., cv. Neepawa), the low rate (0·02 kg ha^-1) of chlorsulfuron significantly reduced wild oat control from individual applications of only barban and diclofop-methyl. The high rate (008 kg ha^-1) affected wild oat control by all four graminicides, including difenzoquat and flam-prop-methyl. In most cases, the graminicides did not affect the broad-leaved weed control of chlorsulfuran. Overall, a low rate of chlorsulfuron in mixture with graminicides did not reduce wheat yield, whereas a high rate of chlorsulfuron in the mixtures gave a significant yield reduction compared with individual graminicides applied alone. All herbicide treatments increased wheat yield over the control. In the glasshouse, reduction in wild oat control by diclofop-methyl was directly related to the rate of chlorsulfuron added to diclofop-methyl. The effect of 0·02 kg ha^-1 chlorsulfuron on control of wild oat was decreased when the rate of diclofop-methyl increased from 0·5 to 0·9 kg ha^-1 and was completely eliminated when diclofop-methyl reached 1·1 kg ha^-1. Conversely, diclofop-methyl (0·7 and 1·1 kg ha^-1) gave some reduction of wild mustard (Sinapis arvensis L.) and redroot pigweed (Amaranthus retrofiexus L.) control by chlorsulfuron (0·01 and 0·02 kg ha^-1), even though in some cases diclofop-methyl/chlorsul-furon gave better control of these broad-leaved weeds. In the laboratory, the absorption and translocation of [¹⁴C]-diclofop-nieihyl in wild oat seedlings were significantly reduced when chlorsulfuron was added, compared with [¹⁴C]-diclo-fop-methyl applied alone. Effet du chlorsulfuron sur l'efficacité et l'effet sur le rendement de quatre graminicides Dans des essais de plein champ sur blé de printemps (Triticuni aestivum L., cv. Neepawa), la faible dose (0, 02 kg ha^-1) de chlorsulfuron a réduit significativement l'efficacité d'une application séparée de barbane et de diclofop-methyl. La forte dose (0, 08 kg ha^-1) a contrarié la destruction de la folle avoine pour les quatre graminicides dont le difenzoquat et le flamprop-methyl. Dans la plupart des cas, les graminicides n'ont pas eu d'incidence sur la destruction des dicotylédones par le chlorsulfuron. Par ailleurs. une faible dose de chlorsulfuron en mélange avec les graminicides n'a pas réduit le rendement en blé, en revanche, une forte dose de chlorsulfuron en mélange a entrainé une baisse significative de rendement en comparaison des graminicides appliqués seuls. Tous les traitements herbicides ont entrainé un gain de rendement par rapport au témoin non traité. En serre, la réduction d'efficacité sur folle avoine du diclofop-methyl était directement correlée à la dose de chlorsulfuron ajouté. Les effets de 0, 02 kg ha^-1 sur la destruction de la folle avoine baissaient quand le niveau de diclofop-methyl augmentait de 0,5 à 0,9 kg ha^-1 et étaient complètement éliminés quand la dose de diclofop-methyl atteignait 1, 1 kg ha^-1. Par ailleurs, le diclofop-méthyl (0,7 et 1,1 kg ha^-1) a réduit l'efficacité du chlorsulfuron (0,01 et 0,02 kg ha^-1) sur la sanve (Sinapis arvensis L.) et l'amaranthe réflechie (Amaranthus retroflexus L.) même si dans certains cas l'association diclofop-mélhyl-chtorsulfuron a eu une meilleure efficacité sur ces mauvaises herbes. Au laboratoire, l'ab sorption et la translocation du diclofop-methyl C¹⁴ dans les plantules de folle avoine ont été réduites significativement par l'addition de chlor-sulfuron en comparaison du diciofop-méthyl C¹⁴ appliqué seul. Wirkung von Chlorsulfuron zusammen mil Vier Graminiziden auf die Unkrautbekämpfung und den Ertrag von Weizen In Freilandversuehen mit Sommerweizen (Triticum aesttotm L. ‘Neepawa’) verminderie Chlorsulfuron in niedriger Aufwandmenge (0,02 kg ha^-1) den Bekämpfungserfolg gegen Flug-Hafer nur bei Barban und Diclofop-menthyl. Die hohe Aufwandmenge (0,08 kg ha^-1)beeinträchtigte die Wirkung aller 4 Graminizide, einschliesslich Difenzoquat und Flamprop-methyl. Die Graminizide beeinfiussten die Wirkung von Chlorsulfuron gegen zweikeimblättrige Arten meistens nicht, Der Weizenertrag blieb bei der Mischung der niedrigen Aufwandmenge von Chlorsulfuron mit den Graminiziden unverändert, die hohe Aufwandmenge führte aber in den Mischungen zu einem signifikaten Abfall des Ertrags, vergli-chen mit dem bei Anwendung der Graminizide allein. Mit allen Herbizidbehandlungen wurden gegenüber Unbehandelt höhere Erträge erzielt. Im Gewächshaus war die Wirkung von Diclofopmethyl gegen Flug-Hafer direkt von der zugefügten Menge an Chlorsulfuron abhängig. Der Einfluss von 0,02 kg ha^-1 Chlorsulfuron aif die Bekämpfung von Fiug-Hafer nahm ab. wenn die Aufwundmenge von Diclofop-methyl von 0,5 auf 0,9 kg ha^-1 gesteigert wurde; bei 1, 1 kg ha^-1 Diclofop-methyl war er aufgehoben. Andererseits trat bei 0,7 und 1,1 kg ha^-1 Diclofop-methyl eine Minderung der Wirkung von Chlosulfuron (0,01 und 0,02 kg ha^-1) gegen Acker-Senf (Sina-psis arvensis L.) und Zurückgekrümmten Fuchsschwanz (Amarenthus retroflexus L.) ein, wenn auch dise Mischung in einigen Fällen gegen dise Arten starker wirkte. Im Labor wurde einc signifikant geringere Absorption und Trans-lokation von ¹⁴C-Diclofop-methyl in Keimpflan-zen des Flug-Hafers beobachtet, wenn Chlorsulfuron zugefügt worden war.     

Mechanism of herbicidal activity of a new cyclohexane-1,3-dione, tepraloxydim to Poa annua L.

Tepraloxydim [(EZ)‐(RS)‐2‐{1‐[(2E)‐3‐chloroallyloxyimino]propyl}‐3‐hydroxy‐5‐perhydropyran‐4‐ylcyclohex‐2‐en‐1‐one] showed high activity against annual bluegrass (Poa annua L.), which is relatively tolerant to sethoxydim [(±)‐2‐(1‐ethoxyiminobutyl)‐5‐[2‐(ethylthio)propyl]‐3‐hydroxycyclohex‐2‐en‐1‐one]. Absorption and translocation rates of tepraloxydim and sethoxydim were higher in P. annua than in Setaria faberi, but the absorption and translocation patterns of tepraloxydim in the two plants were similar to those of sethoxydim. Metabolic rates of tepraloxydim and sethoxydim in P. annua and S. faberi were found to be similar. The concentration for 50% inhibition (I₅₀) of acetyl‐coenzyme A carboxylase (ACCase) with tepraloxydim was approximately 3 × 10^?6 mol L^?1 for P. annua and 7 × 10^?7 mol L^?1 for S. faberi. For sethoxydim, the I₅₀ was found to be 2 × 10^?6 mol L^?1 with the enzyme of S. faberi, while sethoxydim showed a slight effect on ACCase from P. annua activity, even at 10^?4 mol L^?1. The strong inhibition of ACCase with tepraloxydim is considered to be the major factor contributing to the high herbicidal activity against P. annua. Measuring the whole plant growth response, the ratio of the tepraloxydim I₅₀ dose of P. annua to that of S. faberi (P/S) was found to be 2.4, while the P/S ratio of sethoxydim and a tepraloxydim analog with a propyl chain at R₂ were 56.3 and 73.3, respectively. The herbicidal activity against P. annua was remarkably influenced by the length of the R₂ alkyl chain, while the effect on S. faberi was not affected. Acetyl‐coenzyme A carboxylase from P. annua also exhibited a higher resistance to the tepraloxydim analog with a propyl chain than to tepraloxydim. These results suggest that a binding site structure of cyclohexane‐1,3‐diones in the ACCase differs between P. annua and S. faberi.     

In vitro sensitivity of wheat and oat mitochondria to the selective herbicide,diclofop-methyl

Compared to diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate), diclofop (the demethylated derivative) was a more potent inhibitor of polarographically monitored state 3 respiration of mitochondrial preparations isolated from shoots of dark-grown wheat (Triticum aestivum L. cv. Neepawa) and oat (Avena sativa L. cv. Terra) seedlings. Wheat and oat mitochondria demonstrated essentially similar concentration-response patterns for the uncoupler-like stimulation of state 4 respiration and the inhibition of state 3 respiration by diclofop, thereby intimating that differential mitochondrial sensitivity was not a selectivity factor between these species. Diclofop suppression of unconstrained oxygen utilization elicited by the respiratory uncoupler FCCP indicated that inhibition of state 3 respiration involved interference with some site(s) on the mitochondrial electron transport chain and not with energy transfer directly. Cytochrome c oxidase activity was not affected by diclofop, but succinate- and malate-PMS oxidoreductase activities were inhibited by diclofop. Enhanced rates of passive mitochondrial swelling in isotonic KCl medium in the presence of diclofop pointed to a direct influence on the permeability properties of the inner mitochondrial membrane and indicated that membrane disruption could have been a factor in the effects elicited by diclofop on mitochondrial respiration. However, it does not appear that specific interference with mitochondrial functionality is the primary mechanism of phytotoxicity in susceptible plants.     

Response of wheat and oat seedlings to root-applied diclofop-methyl and 2,4-dichlorophenoxyacetic acid

Roots of wheat and oat seedlings were treated with diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate) in a specially designed Plexiglas treatment apparatus. Diclofopmethyl severely inhibited the root growth of susceptible oat seedlings but roots of resistant wheat seedlings were unaffected. Diclofop-methyl at 0.3 μM reduced the growth of oat roots to 50% of the control. Direct contact between diclofop-methyl and the inhibited root zone was necessary for growth inhibition since other parts of the seedling (roots and shoots) isolated from contact with diclofop-methyl solution by a physical barrier were unaffected. Diclofop (2-[4-(2′,4′-dichlorophenoxy)phenoxy]propionic acid), the free acid metabolite of diclofop-methyl, was somewhat more phytotoxic than the parent compound. The herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), which engenders auxin responses, slightly enhanced the inhibition of oat root growth by diclofop-methyl. The primary wheat metabolite, ring-hydroxylated diclofop, was nonphytotoxic to oat root growth, whereas the acetylated derivative of the primary water-soluble oat metabolite (neutral glucose ester of diclofop) inhibited oat root growth to the same extent as diclofop-methyl. These results support the hypothesis that the basis for selectivity between resistant wheat and susceptible oat is the metabolism of diclofop-methyl by aryl hydroxylation and conjugation but not glucose ester conjugation. Translocation is also not an important factor in the phytotoxic activity of diclofop-methyl.     

Metabolism of chlorsulfuron by tolerant broadleaves

The ability of flax and black nightshade to metabolize chlorsulfuron was studied to determine if metabolism contributes to tolerance and to identify any metabolites produced. Plant leaves were treated with [¹⁴C]chlorsulfuron for a 24-hr period. The metabolites were extracted, separated by HPLC, and characterized. Mass spectral analysis and independent synthesis confirmed a major metabolite (B-1) as 2-chloro-N-{[4-(hydroxymethyl)-6-methoxy-1,3,5-triazin-2-yl]amino-carbonyl}benzenesulfonamide. A second major metabolite (B) was determined to be a carbohydrate conjugate of B-1. Plants were more tolerant to B-1 applications than to chlorsulfuron. These results suggest that metabolism may be the basis of selectivity to chlorsulfuron for tolerant broadleaf plants as well as for grasses.     

Fate of chlorsulfuron in the environment. 1. Laboratory evaluations

The behaviour and fate of chlorsulfuron in aqueous and soil systems were examined in laboratory studies. Aqueous hydrolysis was pH-dependent and followed pseudo-first-order degradation kinetics at 25°C, with faster hydrolysis occurring at pH 5 (half-life 24 days) than at either pH 7 or 9 (half-lives >365 days). Degradation occurred primarily by cleavage of the sulfonylurea bridge to form the major metabolites chlorobenzenesulfonamide (2-chlorobenzenesulfonamide) and triazine amine (4-methoxy-6-methyl-1,3,5-triazin-2-amine). This route is a major degradation pathway in water and soil systems. Aqueous photolysis (corrected for hydrolysis) proceeded much more slowly (half-life 198 days) than aqueous hydrolysis and is not expected to contribute significantly to overall degradation. Hydrolysis in soil thin-layer plates exposed to light (half-life 80 days), however, progressed at a much faster rate than in dark controls (half life 130 days), which suggests that a mechanism other than direct photolysis may have been operative. An aerobic soil metabolism study (25°C) in a Keyport silt loam soil (pH 6·4, 2·8% OM) showed that degradation was rapid (half-life 20 days). Dissipation in an anaerobic sediment/water system (initial pH of water phase 6·7, final pH 7·4) progressed much more slowly (half-life >365 days) than in aerobic soil systems. Major degradation products in aerobic soil included the chlorobenzenesulfonamide and triazine amine as in the aqueous hydrolysis study. Neither of these degradation products exhibited phytotoxicity to a variety of crop and weed species in a glasshouse experiment, and both exhibited an acute toxicological profile similar to that of chlorsulfuron in a battery of standard tests. Demethylation of the 4-methoxy group on the triazine moiety and subsequent cleavage of the triazine ring is another pathway found in both aqueous solution and soils, though different bonds on the triazine amine appear to be cleaved in the two systems. Hydroxylation of the benzenesulfonamide moiety is a minor degradation pathway found in soils. Two soils amended with 0·1 and 1·0 mg kg^-1 chlorsulfuron showed slight stimulation of nitrification. The 1·0 mg kg^-1 concentration of chlorsulfuron resulted in minor stimulation and inhibition of ¹⁴C-cellulose and ¹⁴C-protein degradation, respectively, in the same soils. Batch equilibrium adsorption studies conducted on four soils showed that adsorption was low in this system (K_oc 13–54). Soil thin-layer chromatography of chlorsulfuron (R_f=0·55–0·86) and its major degradation products demonstrated that the chlorobenzenesulfonamide (R_f=0·34–0·68) had slightly less mobility and that the triazine amine (R_f=0·035–0·40) was much less mobile than chlorsulfuron. In an aged column leaching study, subsamples of a Fallsington sandy loam (pH_water 5·6, OM 1·4%) or a Flanagan silt loam (pH_water 6·4, OM 4·0%) were treated with chlorsulfuron, aged moist for 30 days in a glasshouse and then placed upon a prewet column of the same soil type prior to initiation of leaching. This treatment resulted in the retention of much more total radioactivity (including degradation products) than by a prewet column, where initiation of leaching began immediately after chlorsulfuron application, without aging (primarily chlorsulfuron parent). © 1998 SCI     

Degradation of the herbicide flamprop-methyl in soil

The degradation of the wild oat herbicide flamprop-methyl [methyl DL -N-benzoyl-N-(3-chloro-4-fluorophenyl)alaninate] in four soils has been studied under laboratory conditions using ¹⁴C-1abelled samples. The flamprop-methyl underwent degradation more rapidly than its analogue flamprop-isopropyl. However, similar degradation products were formed, namely the corresponding carboxylic acid and 3-chloro-4-fluoroaniline. The latter compound occurred mainly as ‘bound’ forms although evidence was obtained of limited ring-opening to give [¹⁴C]carbon dioxide. The time for depletion of 50% of the applied herbicide was approximately 1-2 weeks in sandy loam, clay and medium loam soils and 2-3 weeks in a peat soil.     

A Diclofop-methyl-Resistant Avena sterilis Biotype with a Herbicide-Resistant Acetyl-coenzyme A Carboxylase and Enhanced Metabolism of Diclofop-methyl

An Avena sterilis biotype was found to be highly resistant to aryloxyphenoxypropionate (APP) herbicides, especially diclofop-methyl. At the enzyme level, this biotype contained a modified acetyl-coenzyme A carboxylase (ACCase) with six-fold resistance to diclofop acid. Absorption and translocation of [¹⁴C]diclofop-methyl applied to the leaf axil of the two-leaf stage plants were similar in both susceptible and resistant biotypes. However, the rate of metabolism of [¹⁴C]diclofop was increased 1·5-fold in this resistant biotype compared to the susceptible. Experiments with tetcyclacis, a cytochrome P450 monooxygenase inhibitor, indicated that inhibition of this enhanced diclofop metabolism increased diclofop-methyl phytotoxicity in this biotype. Studies with ten individual families of the resistant biotype indicated that both mechanisms of resistance, an altered target site and enhanced metabolism, are present in each individual of the population. Hence, it is likely that these two mechanisms of resistance both contribute to resistance in this biotype. © 1997 SCI.     

The analysis of crops and soils for the triazine herbicide cyanazine and some of its degradation products. I. Development of method

Radiochemical techniques have been used to develop efficient procedures for the extraction of residues of cyanazine herbicide [‘BLADEX’,

1 BLADEX and FORTROL are Shell registered Trade Marks.

^a ‘FORTROL’,^a 2-chloro-4-(1-cyano-1-methylethylamino)-6-ethylamino-1,3,5-triazine] and its metabolites 2-chloro-4-(1-carbamoyl-1-methylethylamino)-6-ethylamino-1,3,5-triazine ( II ), 2-chloro-4-(1-cyano-1-methylethylamino)-6-amino-1,3,5-triazine ( V ) and 2-chloro-4-(1-carbamoyl-1-methylethylamino)-6-amino-1,3,5-triazine ( VI ) from crops and soils. Partition and column chromatographic techniques have been established for the purification of the extracts. The full analytical procedure is described and the final determination of all four compounds is by g.l.c. with electron capture detection with blank values for field samples generally 0.02 part/million and with good recoveries.     

A bioassay method for formulation testing and residue studies of sulfonylurea and sulfonanylide herbicides

A bioassay method using the radicles of pea (Pisum sativum L.) and lupin (Lupinus angustifolius L.) was developed for the assessment of trials on herbicides of common use in the sulfonylurea class (chlorsulfuron, triasulfuron and metsulfuron-methyl) and in the sulfonanylide class (flumetsulam and metosulam). Soils within a range of pH 5.8–8.4 with textures from sand to clay were used in these experiments. The sensitivities of the species were similar in chlorsulfuron and flumetsulam trials and their response range varied with soil type and herbicide, e.g. between 0.75 and 6.0 ng triasulfuron g^?1 in the Wimmera grey clay and between 0.125 and 8.0 ng chlorsulfuron g^?1 soil in the Mallee sand. The method was demonstrated in a wide range of uses, encompassing tests of the initial bioactivity of formulations of chlorsulfuron and flumetsulam, monitoring the field leaching and persistence of triasulfuron and measuring relative potencies between the classes, using metsulfuron-methyl and metosulam. The bioassay response provided a high level of reproducibility and precision, which was measurable by the logistic curve-fitting procedure. In each case, R² values were >0.90 and lack-of-fit tests were clearly non-significant at the 0.05 level. Chi-square tests were used to measure differences between ED₅₀'s. The method does not require the pre-germination and selection of seedlings, daily watering or root-washing and results are obtained 7 days from sowing, providing favourable use for routine analyses and large-scale trials.     

Uptake and phytotoxicity of chlorsulfuron in Zea mays L. in the presence of 1,8-naphthalic anhydride

The sites of uptake of chlorsulfuron in maize (Zea mays L.) were investigated at three different growth stages. Exposure of seedling roots, or shoots separately, to herbicide-treated sand over 4 days resulted in inhibition of both roots and shoots. Exposure of seedling roots to chlorsulfuron-treated soil over 21 days severely inhibited both roots and foliage, while separate shoot exposure also reduced both foliage and root growth. After plant emergence, exposure of the crown root node, growing point and lower stem to treated soil reduced foliage and root growth, but exposure of the shoot above the growing point caused only slight inhibition of foliage and had no effect on roots. The herbicide safener 1,8-naphthalic anhydride (NA) applied as a dust (10 g kg^?1 seed weight), or as a 50 mg 1^?1 suspension in water to maize seeds, reduced the root inhibition by chlorsulfuron in 4-day-old seedlings. NA completely prevented both foliage and root injury when chlorsulfuron was placed in soil in the shoot zone before emergence, or in the shoot zone below the soil surface after plant emergence. NA slightly decreased injury to foliage, but not to roots when chlorsulfuron was placed in soil in the root zone before emergence. NA seed treatment protected both roots and foliage against injury from foliarly applied chlorsulfuron. Plants were also protected when a suspension of NA in water was sprayed on the foliage seven days before chlorsulfuron. When a mixture of NA and chlorsulfuron was applied to foliage, root injury was reduced more than foliage injury.     

Bioavailability of conjugated and soil-bound [14C]‘hydroxymonolinuron’-β-D-glucoside residues to earthworms and ryegrass

The β-D -glucoside conjugate of [¹⁴C]‘hydroxymonolinuron’, [phenyl-¹⁴C]-3-(4- chlorophenyl)-1-(hydroxymethyl)-1-methoxyurea-β-D -glucoside (HM-β-G) and its soil-bound residues, prepared as described, were used to estimate its bioavailability to earthworms and ryegrass plants. The results demonstrate that these bound residues were available to both earthworms and ryegrass. The concentration in the earthworms, expressed on a dry weight basis after 42 days of exposure, was equal to the surrounding soil. The earth worms were found to be more efficient in remobilising and absorbing soil-bound residues than ryegrass plants after 59 days of cultivation. Fractionation of the soil-bound residues showed that 29% of the radiocarbon was associated with fulvic acid, 20% with humic acid and 9% with the humin fraction. 4-Chlorophenylurea, a metabolite of HM-β-G proved to be a key compound in the formation of soil-bound residues. The amount of radioactivity (bound residues), recovered from soil through solubilisation by means of 0.5M -acid and alkali, seems to be a criterion for predicting the bioavailability of bound phenylurea residues. The half-life of soil-bound residues was estimated to be about 4.6 years.     

Model Predictions and Field Measurements of Chlorsulfuron Leaching under Non-steady-state Flow Conditions

Model simulations of chlorsulfuron (1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea) leaching in a loamy soil were made with the mechanistic dual-porosity model MACRO. Comparisons were made with a data set obtained in a lysimeter experiment in which leaching was measured during an 11-month period after applying chlorsulfuron at two rates (4 and 8 g ha⁻¹). In this experiment, peak concentrations appeared c.6 months after pesticide application, reaching levels of 14 and 21 ng litre⁻¹ in the low- and high-dose treatments, respectively. These peak concentrations appeared after c.70 mm of accumulated leachate, implying that some of the herbicide was displaced through the soil columns by non-equilibrium flow processes. Model calibration was limited to parameters related to evapotranspiration, water uptake by roots and degradation rates in the subsoil. With this minimum amount of calibration, the model successfully described the leaching pattern of chlorsulfuron, provided that the two-flow domain option in the model was used. Running the model in one-flow domain resulted in considerable underestimates of leaching of chlorsulfuron over the short-term (<1 year). The degradation rate in the subsoil was also found to be critical. It had to be increased about fivefold to match measured chlorsulfuron concentrations in leachate. At such concentrations, 0·012 g ha⁻¹ of chlorsulfuron (0·3% of that applied) was predicted to leach through the soil profile during the 11-month simulation period when the lower dose of the compound was applied.