Metabolism of chlorsulfuron by plants: Biological basis for selectivity of a new herbicide for cereals

A major factor responsible for the selectivity of chlorsulfuron [2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide] (formerly DPX-4189), as a postemergence herbicide for small grains is the ability of the crop plants to metabolize the herbicide. Chlorsulfuron is the active ingredient in Du Pont “Glean” weed killer. Tolerant plants such as wheat, oats, and barley rapidly metabolize chlorsulfuron to a polar, inactive product. This metabolite has been characterized as the O-glycoside of chlorsulfuron in which the phenyl ring has undergone hydroxylation followed by conjugation with a carbohydrate moiety. Sensitive broadleaf plants show little or no metabolism of chlorsulfuron.     

光敏型氯磺隆与普通氯磺隆的控草效果比较

比较了光敏型氯磺隆与普通氯磺隆不同剂量对各种杂草的控制效果。结果显示在低剂量下,普通氯磺隆的控草效果略高于光敏型氯磺隆。在中量、高量和倍量下,两种制剂控草效果差异不大。     

Phytotoxicity and persistence of chlorsulfuron as affected by activated charcoal

Two bioassay procedures, using petri-dishes and pots, based on the root growth of pregerminated maize were used to study the residual phytotoxicity of chlorsulfuron under field conditions. Both bioassay procedures appeared to be equally reproducible and sensitive with residues of chlorsulfuron being detectable from 0·25 to 10·0 ng g^-1. The results indicated that persistence, movement and phytotoxicity increased with increasing rate of chlorsulfuron, but persistence of the herbicide was shorter in wet compared to dry field conditions. As little as 1 g a.i. ha^-1 of incorporated chlorsulfuron under warm and dry field conditions caused a stunting effect on maize plants (Hybrid F₁, Damon) and reduced yield by 53% compared to untreated control plants; while 5·0 and 10·0 g a.i. ha^-1 of incorporated chlorsulfuron killed all maize plants. However, under wetter field conditions, incorporated chlorsulfuron at 1·25, 2·5 and 5·0 g a.i. ha^-1 caused a stunting effect on maize plants (Hybrid F₁, ARIS) and decreased yield by 16, 57 and 92%, respectively, compared to untreated control. Incorporation of 50 kg ha^-1 of activated charcoal inactivated completely chlorsulfuron incorporated at 1·25 and 2·5 g a.i. ha^-1 and did not affect yield of maize compared to untreated control. Higher rates of activated charcoal such as 100 and 200 kg ha^-1 also inactivated chlorsulfuron applied at 1·25–5·0 g a.i. ha^-1 and did not affect grain yield of maize. Phytotoxicité et persistance du chlorsulfuron Deux méthodes d'essais biologiques, à savoir en boîte de Petri ou en pot, Basées sur la croissance des racines de maïs prégermé ont été utilisées pour étudier la phytotoxicité résiduelle du chlorsulfuron en conditions de plein champ. Les deux méthodes sont également reproductibles et sensibles à des niveaux de détection pour les résidus de chlorsulfuron de 0,25 à 10 ng g^-1. Les résultats montrent que la persistance et la phytotoxicité augmentent avec des doses croissantes de chlorsulfuron, mais la persistance est plus courte dans des conditions de plein champ humides que séches. Une dose aussi faible que 1 g de matiére active ha^-1 de chtorsulfuron incorporé en conditions chaudes et séches a causé un effet retard sur les plants de maïs (hybride F₁, Damon) et a réduit de 53% le rendement par rapport au témoin non traité; des doses de 5 à 10 g de matiére active ha^-1 de chlorsulfuron incorporé ont tué tous les pieds de maïs. Cependant, en conditions plus humides, le chlorsulfuron incorporéà 1,25, 2,5 et 5 g de matiére active ha^-1 a causé un effet retard sur le maïs (hybride F₁ ARIS) et a réduit le rendement par rapport au témoin non traité respectivement de 16, 57 et 92%. L'incorporation de 50 kg ha^-1 de charbon actif a complément inactive le chlorsulfuron incorporéà 1,25 et 2,5 g de matiére active ha^-1 et n'a pas eu de répercussion sur le rendement par rapport au témoin non traité. Des doses plus élevées de charbon actif comme 100 et 200 kg ha^-1 ont inactivé le chlorsulfuron appliquéà 1,25–5 g matiére active ha^-1et n'ont pas affecté le poids en grain du maïs. Ueber die Beeinflussung von Phytotoxizität und Wirkungsdauer von Chlorsulfuron durch Aklivkohle Zum Studium der Residualwirkung von Chlorsulfuron unter Feldbedingungen wurden zwei Bioassaymethoden, eine in Petrischalen, die andere in Töpfen, eingesetzt. Beide Methoden basierten auf dem Wurzelwachstum von vorgekeimtem Mais. Es zeigte sich, dass beide Versuchsverfahren in gleichem Masse reproduzierbar und empfindlich und in der Lage sind Rückstände von 0,25–10,0 ng g^-1 nachzuweisen. Mit steigender Chlorsulfurondosis wurde eine zunehmende Phytotoxizität, Persistenz und Mobilität des Herbizids festgestellt. Die Persistenz war unter feuchten Feldbedingungen kürzer als bei Trockenheit. Bis zu einer unteren Grenze von 1,0 g a.i. ha^-1 verursachte inkorporiertes Chlorsulfuron, unter trockenen und warmen Feldbedingungen an Mais (Hybride F₁, Damon) Wachstumshemmungen und Erntereduktionen von 53%, verglichen mit unbehandelten Kontrollpflanzen. Unter feuchteren Bedingungen, jedoch, hatten 1,25, 2,5 and 5,0 g a.i. ha^-1 eingearbeitetes Chlorsulfuron an Mais (Hybride F₁ ARIS) Wachstumshemmungen und Ernteverluste von 16, 57 und 92% zur Folge. Die Einarbeitung von 50 kg ha^-1 Aktivkohle inaktivierte 1,25 g und 2,5 g ha^-1 inkorporierles Chlorsulfuron vollständig und hatte keinerlei negative Auswirkungen auf die Maisernte, im Vergleich zu unbehandelten Kontrollen. Höhere Mengen von Aktivkohle, wie 100 und 200 kg ha^-1, inaktivierten auch Chlorsulfuronmengen von 1,25–5 g ha^-1 und hatten keinen Einfluss auf den Kömerertrag.     

除草剂解毒剂减轻氯磺隆残留对玉米药害的研究

采用室内生物测定方法,研究了除草剂解毒剂5-二氯乙酰基-3,6-二甲基-3-乙基-9-氧代-1,5-二氮杂二环[4.3.0]壬烷减轻氯磺隆对玉米的伤害作用。结果表明:随着土壤中氯磺隆浓度的增大,玉米的生长受到抑制,用解毒剂浸种处理后,可在一定程度上减轻氯磺隆对玉米生长的影响。当土壤中氯磺隆残留量为2μg/kg时,解毒剂浓度在1～5mg/kg时解毒效果最佳,玉米株高、株鲜重、根长、根鲜重的恢复率最高可达101.27%、63.74%、73.29%和51.81%。     

Metabolism of chlortoluron in tolerant species: possible role of cytochrome P-450 mono-oxygenases

Pathways of chlortoluron metabolism were compared in excised leaves of four tolerant species, namely wheat (Triticum aestivum var Clement), Bromus sterilis, Galium aparine and Veronica persica. The herbicide was principally detoxified by hydroxylation of the ring methyl in wheat and by N-dealkylation in Veronica persica. Both pathways were involved in Bromus sterilis and Galium aparine. Kinetic study of the degradation showed that capacity to form non-toxic conjugates could, at least partially, explain the tolerance of these species to chlortoluron. In plants treated with 1-aminobenzotriazole, a cytochrome P-450 enzyme inactivator, N-dealkylation of chlortoluron was little or not affected, but ring methyl hydroxylation was strongly inhibited. This suggests that at least two distinct enzymatic systems could participate in this metabolism. Moreover, cytochrome P-450 enzymes could be involved in the ring methyl hydroxylating reaction.     

土壤中砜嘧磺隆和氯磺隆残留的光化学荧光分析方法研究

用紫外线照射非荧光特性的砜嘧磺隆和氯磺隆,通过生成具有荧光特性的衍生物,分别研究了其在不同介质中的荧光特性及其影响因子,建立了测定土壤中砜嘧磺隆和氯磺隆残留的光化学荧光分析法(PCF)。结果表明:在2×10-3 mol/L、一定酸碱度(砜嘧磺隆pH 7、氯磺隆pH 12)的十六烷基三甲基氯化铵(CTAC)胶体分散体系中,紫外照射150 s是PCF法测定砜嘧磺 隆和氯磺隆残留的最佳条件,在此条件下砜嘧磺隆和氯磺隆的检出限(LOD)分别为0.7和0.6 μg/kg, 相对标准偏差(RSD)分别为1.7%和2.1%;在黄松田水稻土、黄红壤性水稻土和青紫泥田水稻土3种不同性质的土壤中,砜嘧磺隆和氯磺隆同时测定的平均回收率分别为99.0%±1.0%和98.7%±4.1%、97.6%±1.7%和97.0%±4.7%、96.7 %±2.3%和95.4%±5.5%;所建立的PCF法可有效、快速测定土壤中同时残留的微量砜嘧磺隆和氯磺隆。     

Photolysis of chlorsulfuron and metsulfuron-methyl in methanol

Photolysis of chlorsulfuron and metsulfuron-methyl was studied in methanol under UV light. Their rates of primary photolysis followed first-order kinetics. The main photoproducts were identified as 2-methoxy-4-methyl-1,3,5-triazin-6-amine, 2-chloro-benzenesulfonamide and methyl 2-(aminosulfonyl)benzoate, which entailed the cleavage of the two N–C ureic bonds. Further photolysis of benzenesulfonamide derivatives involved oxidation of −NH₂, cyclisation with loss of CH₃OH, and scission of the C–S bond A trace of methyl o-mercaptobenzoate was also detected. The corresponding photolysis pathways of chlorsulfuron and metsulfuron-methyl were tentatively proposed. © 1999 Society of Chemical Industry     

Rates of chlorsulfuron degradation in three Brazilian oxisols

The degradation of chlorsulfuron was studied in laboratory experiments in three oxisols from south and south–east Brazil. Three soil profiles were sampled by horizon, and classified according to USDA soil taxonomy and the Brazilian system. Degradation assays were made to evaluate the influence of temperature, humidity and liming on chlorsulfuron decomposition. Further experiments were set up to study enhanced biodegradation. Abiotic degradation was also studied in sterile soils, to evaluate, by comparison with non–sterile soils, the role of microorganisms in degradation. The degradation always followed first–order kinetics and was generally faster in samples from A than B horizons. An increase in temperature (from 25 to 40°C) increased chlorsulfuron degradation. Further, an increase in moisture content increased chlorsulfuron degradation in samples from the A horizons of all soils, whereas for two out of three soils, degradation in samples from the B horizon was greater at lower water content. The biotic contribution to degradation was significant only for the soil with higher fertility. Soil liming significantly increased chlorsulfuron half–life in all samples. Significant enhancement of degradation (decrease in half–life on reapplication) was observed only in soil from A horizons, where a higher microbial activity was likely.     

Kinetics and hydrolysis mechanism of chlorsulfuron and metsulfuron-methyl

In acidic media, hydrolysis of chlorsulfuron and metsulfuron-methyl occurs via two consecutive reactions which were followed by ultraviolet spectrophotometry. For these two reactions, the pseudo-first-order rate constants increase proportionally to the concentration of hydronium ion in the more acidic media and to the square of this concentration at higher pH values. A kinetic study by HPLC shows that the first reaction leads to the formation of 4-methoxy-6-methyl-1,3,5-triazin-2-amine and (o-chlorophenylsulfonyl) carbamic acid for chlorsulfuron or (o-methoxycarbonylphenylsulfonyl) carbamic acid for metsulfuronmethyl. The second reaction is the conversion of these sulfonylcarbamic acids to sulfonamides and carbon dioxide. The complete lack of saccharin and of o-sulfamoyl benzoic acid proves that the ester function of the methoxycarbonyl group is stable. The lack of general acid-base catalysis and a solvent deuterium isotope effect less than unity are consistent with a rate-determining cleavage of the protonated substrate. In the basic pH range (10–14) a single reaction occurs, the nucleophilic substitution of the methoxy group on the triazine by a hydroxide group.     

Alcoolyse et hydrolyse chimique acide du chlorsulfuron

Alcoholysis and acid chemical hydrolysis of chlorsulfuron Alcoholysis of chlorsulfuron by methanol or ethanol only involved the urea function of the molecule. The formation of carbamate indicated that isocyanate was probably involved as an intermediate. The chemical degradation of chlorsulfuron in acidic aqueous solution involved two pathways: hydrolysis of the urea function and hydrolysis of the methoxy radical. Increasing the temperature from 25 to 55°C en-hanced the rate of the reaction and favoured hydrolysis of the urea function. Decreasing the pH from 6-0 to 2-4 strongly accelerated degradation and lowered the activation energy without affecting selectivity. Other factors, such as the presence of clays or cations of various transition metals, generally had only limited effects.     

Acetolactate synthase activity and chlorsulfuron sensitivity of wheat cultivars

Differences were observed in the sensitivity of three wheat (Triticum aestivum L.) cultivars to chlorsulfuron. Shoot dry weight was reduced by foliar applications of chlorsulfuron to a greater extent in cv. Rongotea than in cvs Lancer and Kotare. There was no difference between these cultivars in the specific activity of acetolactate synthase (ALS) enzyme extracted from leaves or roots. Moreover, chlorsulfuron inhibited ALS from the wheat cultivars to the same extent in?vitro. ALS measurement in vivo showed that after 15 h of incubating excised leaf tissues with chlorsulfuron, there was a greater reduction in ALS enzyme activity in Rongotea than in the other cultivars. Furthermore, 1 day after a foliar application of chlorsulfuron, in vitro ALS activity in leaves was reduced more in Rongotea than in Lancer or Kotare. Recovery of the enzyme activity following chlorsulfuron application was quicker in Kotare than in Lancer or Rongotea. It is concluded that differences in sensitivity of these wheat cultivars to chlorsulfuron are not due to differential ALS sensitivity or level, but may be due to differential rates of herbicide metabolism.     

The mechanism of differential response of wheat cultivars to chlorsulfuron

Wheat (Triticum aestivum L.) cultivars showed differential tolerance to chlorsulfuron. Cultivar Kotare showed no injury symptoms following foliar applications of chlorsulfuron at 15 or 60 g a.i. ha^?1, while cultivars Rongotea and Lancer showed early damage in pot and field experiments at both rates of chlorsulfuron. Cultivars Abele and Jasper were intermediate in their response. The number of spikelets per ear was the only yield component affected by chlorsulfuron and was reduced in Lancer and Rongotea. Retention, uptake and transiocation of chlorsulfuron were not different between Kotare and Ron-gotea. Within 48 h of application, Kotare metabolized 92–2% of [¹⁴C]chlorsulfuron, while Lancer and Rongotea metabolized only 43–5% and 63% of the herbicide, respectively. The concentration of chlorsulfuron in young tissues of Kotare, Lancer and Rongotea, 48 h after application was calculated as 1.2, 31.9 and 15.6 ng g^?1 dry weight, respectively. It is concluded that differential rates of metabolism are the main reason for differences in sensitivity to chlorsulfuron between the wheat cultivars tested. Le mécanisme des différences de tolérance au chlorsulfuron entre variétés de blé Des variétés de blé (Triticum aestivum L.) ont montré des différences de tolérance au chlorsul-furon. On n'a aucun symptôme de phytotoxicité sur la variété‘Kotare’ après une application foliaire de chlorsulfuron à 15 ou 60 g m.a. ha^?1, alors que les variétés ‘Rongotea’ et ‘Lancer’ présentaient des symptômes précoces aux deux doses, dans des expériences en pot et au champ. La réponse des variété‘Abele’ et ‘Jasper’était intermédiaire. Le nombre de grains par épillet était la seule composante du rendement affectée parle chlorsulfuron et était réduit chez Lancer et Rongotea. La rétention, la pénétration et la migration de chlorsulfuron n'était pas différentes entre Kotare et Rongotea. Quarante huit heures après le traitement, Kotare avait metabolise 92,2% du [¹⁴C]chlorsulfuron, alors que Lancer et Rongotea ne métabolisaient que respectivement 43,5 et 63% de l'herbicide. La concentration de chlorsulfuron dans les tissus jeunes de Kotare, Lancer et Rongotea 48 h après la traitement a étéévaluée à respectivement 1,2,31,9 et 15,6 ng g^?1 de matière sèche. Il est conclu que des différences de vitesse de métabolisation sont la raison principale des différences de sensibilité au chlorsulfuron observées chez les variétés de blé testées. Mechanismen der unterschiedlichen Reaktion von Weizensorten auf Chlorsulfuron-Behandlun-gen Es wurde eine unterschiedliche Toleranz bei Weizensorten (Triticum aestivum L.) gegenüber Chlorsulfuron-Behandlungen beobachtet. Bei der Sorte ‘Kotare’ traten nach Behandlungen mit 15 oder 60 g AS ha keine Schadsymtome auf, während die Sorten ‘Rongotea’ und ‘Lancer’ sowohl in Topfals auch in Freilandversuchen bei beiden Dosen frühe Schädigungen erlitten; die Sorten ‘Abel’ und ‘Jasper’ reagierten mittelstark. Unter den Ertragskomponenten war nur die Zahl der Ährchen pro Ähre betroffen, sie war bei ‘Lancer’ und ‘Rongotea’ reduziert. Aufnahme und Translokation des Wirkstoffs waren bei ‘Kotare’ und ‘Rongotea’ gleich. Bei ‘Kotare’ war [¹⁴C]Chlorsulfuron 48 h nach der Applikation zu 92,2 % metabolisiert, bei ‘Rongotea’ zu 63 % und bei ‘Lancer’ zu 43,5 %. In jungen Geweben dieser Sorten lagen die Chlor-sulfuron-Konzentrationen 48 h nach der Anwendung bei 1,2, 15,6 und 31,9 ng g^?1 TM. Die unterschiedlichen Metabolisierungsraten bei den untersuchten Weizensorten wurden für den Hauptgrund für die Toleranzunterschiede gegenüber Chlorsulfuron gehalten.     

蔺草茬晚稻田防止绿磺隆药害试验初报

蔺草田因长期使用化学除草剂绿磺隆,造成在土壤中残留,严重抑制了后茬晚稻等作物生长,导致僵苗而减产。使用僵苗丰、绿芬威4号、磷酸二氢钾、九二○等微肥和生长调节剂,在晚稻苗期喷施2~3次后,能明显地恢复受害晚稻的生长,株高、穗长、分蘖均表现有一定程度增加,有明显的增粒及增穗作用,增产幅度为25.8%~1.5%,平均增产12.5%。     

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 chlorsulfuron and triasulfuron in alkaline soils under laboratory conditions

The degradation of chlorsulfuron and triasulfuron was investigated in alkaline soils (pH 7.1–9.4) spiked at 40 μg a.i. kg^–1 under laboratory conditions at 25 °C and a moisture content corresponding to 70% field capacity (–33 kPa), using high-performance liquid chromatography. Degradation data for the two herbicides did not follow first-order kinetics, and observed DT₅₀ values in surface soils ranged from 19 to 42 days and from 3 to 24 days for chlorsulfuron and triasulfuron respectively. Disappearance of both chlorsulfuron and triasulfuron was faster in non-sterile than in sterile soil, demonstrating the importance of microbes in the breakdown process. The persistence of chlorsulfuron increased with increasing depth, which can be attributed to the decline in the microbial populations down the profile. The DT₅₀ value for chlorsulfuron at 30–40 cm depth was nearly four times higher than that in the top-soil. The results obtained show that persistence of these herbicides in alkaline surface soils at 25 °C and at a moisture content of 70% field capacity is similar to those reported in other European and North American soils. The study shows that if these herbicides are contained in surface soil layers, the risk of residue carry-over under southern Australian conditions is small. However, the rate of their degradation in alkaline subsoils is very slow, and under conditions conducive to leaching their prolonged persistence in the soil profile is possible.     

Response of Brassica napus in tissue culture to metsulfuron-methyl and chlorsulfuron

A herbicide bioassay based on tissue cultures of Brassica napus L. was evaluated with selected sulfonylurea herbicides. Data were analysed by fitting the results to a log-logistic dose–response model. Within an experiment, the non-linear regression models were fitted simultaneously to the individual dose–response curves. The results obtained showed good response to even low concentrations of herbicide, with detection limits in the range 0.008–0.69 nmol L^?1 for chlorsulfuron and 0.02–0.13 nmol L^?1 for metsulfuron. The reproducibility of the assays, on the basis of coefficient of variation of the ED₅₀ values, was found to be 44% for chlorsulfuron and 48% for metsulfuron measurements. Assay of herbicide dissolved in aqueous soil extract showed significant interference from this matrix on the response, requiring a five times dilution of the extract to overcome this matrix effect.     

The mode of action of chlorsulfuron: A new herbicide for cereals

Chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesul-fonamide) is the active ingredient in DuPont “Glean” Weed Killer (formerly DPX-4189), a new herbicide for weed control in small grains as well as other uses. Continuous growth measurements of chlorsulfuron-sensitive seedlings demonstrated that the herbicide inhibits growth within 2 hr of application and by 8 hr reduces growth by 80%. This reduction in growth was closely associated with an inhibition of plant cell division. No significant effects were observed on auxin-, cytokinin-, or gibberellin-induced cell expansion. Photosynthesis, respiration, RNA synthesis, and protein synthesis were also initially unaffected under conditions where plant cell division is strongly inhibited.     

Comparison of chlorsulfuron and metsulfuron for control of Allium vineale L.

The response of natural and planted stands of Allium vineale L. to chlorsulfuron and metsulfuron was determined in field experiments in Illinois, U.S.A., in 1982 and 1983. In natural stands very low rates of either herbicide controlled A. vineale. Chlorsulfuron, applied in the spring at 20 g ha^?1, reduced aerial bulblet production by 99% but when it was applied in the fall it reduced aerial bulblet production by only 59%. All rates of metsulfuron (5–20 g ha^?1), at both times of application, effected better than 94% reduction in plant density and yield of aerial bulblets. In a glasshouse experiment, plants derived from aerial bulblets were more susceptible to chlorsulfuron than plants derived from soft offset bulbs. Soft offset bulbs were, therefore, used to establish a uniform stand of A. vineale in the field. In this experiment, non-linear regression analysis showed that metsulfuron was two to three times more active than chlorsulfuron. GR₉₅ values calculated from the computed regression equations show that metsulfuron and chlorsulfuron, applied in April at 5 and 15 g ha^?1, respectively, reduced aerial and underground bulb production by 95%.     

Resistance of Raphanus raphanistrum to chlorsulfuron in the Republic of South Africa

Herbicide resistance poses a substantial threat to the agricultural industry throughout the world and during the past decade several reports regarding herbicide resistance have been published. Raphanus raphanistrum L., from two wheat farms located in the winter rainfall region of South Africa, showed indications of resistance to chlorsulfuron. Seeds from these suspected resistant biotypes as well as seeds from a susceptible biotype were collected and transported to the ARC-Small Grain Institute for herbicide resistance studies. Herbicides registered for R. raphanistrum control, i.e. chlorsulfuron, MCPA and bromoxynil, were used in this study. Significant differences in the degree of control were found between the susceptible and two resistant biotypes, when treated with chlorsulfuron. The LD₅₀ values for the resistant biotypes (WR 1 & WR 2) were 45 and 11.3 g a.i. ha^–1, respectively, whereas the LD₅₀ value for the susceptible biotype was 5.6 g a.i. ha^–1. The almost eightfold difference between the susceptible and resistant biotype (WR 1), indicated that resistance has developed to chlorsulfuron. Only twofold resistance was established between the other resistant biotype (WR 2) and the susceptible biotype. Significant differences between herbicide rates were also established with the MCPA and bromoxynil experiments. No significant difference could, however, be found between the susceptible and resistant biotypes when treated with MCPA and bromoxynil, indicating the importance of different modes of action of herbicide as a strategy to prevent herbicide resistance.     

Sublethal effects of chlorsulfuron on black bindweed (Polygonum convolvulus L.)

Effects of the herbicide chlorsulfuron on growth and reproduction of black bindweed (Polygonum convolvulus L.) plants were investigated in a controlled environment chamber and a greenhouse over a full life cycle. Biomass of P. convolvulus was stimulated at 0.4 g a.i. ha^?1, but at higher doses it was reduced compared with controls. Leaf production of plants treated with 1.6 g a.i. ha^?1 was initially totally inhibited, but these plants resumed leaf production 10 days after treatment. Chlorsulfuron treatment resulted in higher proportions of small and large leaves compared with controls. Because the life-span of the plants increased with increasing doses of chlorsulfuron, seed production was not affected at doses up to 1.6 g ha^?1, even though significant effects were found on both biomass and leaf production. At rates of 1.6–4 g a.i. ha^?1 seed production decreased. Plant mortality was low in this study, reaching 33% at the highest rate of chlorsulfuron. Effets sublétaux du chlorsulfuron sur la renouée faux-liseron (Polygonum convolvulus L.) Les effets du chlorsulfuron sur la croissance et la reproduction de la renouée faux-liseron (Polygonum convolvulus L.) ont étéétudiés en serre et en conditions controlées sur un cycle complet. La biomasse de P. convolvulusétait stimulée à 0,4 g m.a. ha^?1 mais à doses plus élevées elle était réduite par rapport à celle des témoins. La production de feuilles de plantes traitées à 1,6 g m.a. ha^?1était initialement totalement inhibée mais ces plantes reprenaient leur production de feuilles 10 jours après le traitement. Les plantes traitées au chlorsulfuron avaient une plus grande proportion de feuilles petites et grandes que les témoins. Comme la durée de vie des plantes s'accroissait avec la dose de chlorsulfuron, la production de graines n'était pas affectée jusqu'à la dose 1,6 g m.a. ha^?1, meme si des effets significatifs étaient détectés sur la biomasse et la production de feuilles. À des doses comprises entre 1,6 et 4 g m.a. ha^?1, la production de graines diminuait. La mortalité des plantes était faible dans cette étude, atteignant 33%à la plus haute dose de chlorsulfuron. Subletale Wirkungen von Chlorsulfuron auf den Gemeinen Windenknoterich (Polygonum convolvulus L.) In Ecophyt- und Gewachshausversuchen zur Wirkung von Chlorsulfuron auf Wachstum und Reproduktion des Gemeinen Windenknoterichs (Polygonum convolvulus L.) war die Biomassebildung bei 0,4 g AS ha^?1 verstarkt, bei hoheren Dosen jedoch verringert. Bei 1,6 g AS ha^?1 war die Blattentwicklung zunachast fur 10 Tage nach der Behandlung ganzlich unterdruckt. Der Anteil kleinerer und großerer Blatter war hoher. Mit zunehmendem Aufwand des Herbizids verlangerte sich der Entwicklungszyklus, so daß bis zu 1,6 g AS ha^?1 die Samenproduktion nicht zuruckging, trotz signifikanter Wirkung sowohl auf die Biomasse als auch auf die Blattbildung. Bei Dosen Uber 1,6 bis 4,0 g AS ha^?1 wurden weniger Samen gebildet. Die Absterberate war bei diesen Versuchen niedrig und betrug bei der hochsten Chlorsulfuron-Dosis 33%.