The degradation of methazole in soil. II. Studies with methazole,methazole degradation products and diuron

[¹⁴C]-Labelled methazole, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl)urea (DCPU), and diuron were incubated in soil at 20°C and field capacity soil moisture content. Decomposition followed first-order kinetics; half-lives for degradation of these four compounds were 2.4, 144, 30 and 108 days respectively. The amount of DCPMU and DCPU that could be extracted decreased with time and the decrease was accompanied by the generation of an equivalent amount of ¹⁴CO₂. This was not so in the studies with diuron and methazole, however, and the decrease in the concentrations of radioactivity extracted from soil treated with these compounds could not be entirely accounted for as carbon dioxide. It is concluded that the unextractable radiochemical that was present was DCPMU. Methazole appeared to be degraded through DCPMU to 3,4-dichloroaniline (DCA) with the production of only traces of DCPU.     

Aspects of the selective phytotoxicity of methazole. HI. Behaviour in plants following foliar treatment

Absorption of methazole by leaves of onion (Allium cepa), Stellaria media, Matricaria matricarioides and Veronica persica was rapid for the first 24 h after treatment and continued at a slower rate for up to 6 days to reach a maximum of between 35 and 60% of the amount applied. Differences in absorption between species were generally small. Absorption by the cotyledon of onion was greater than absorption into true leaves. Methazole on the leaf surface degraded to 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and small amounts of this degraded to 3-(3,4-dichlorophenyl) urea (DCPU). Methazole absorbed into leaves was relatively stable in M. matricarioides and DCPMU accumulated slowly. The rate of degradation was more rapid in the cotyledons than in the true leaves. Both in leaves and in cotyledons of onion and S. media, methazole degraded rapidly to DCPMU and this accumulated; in those of V. persica, DCPMU was degraded quickly to DCPU and unidentified products. The amount of DCPMU accumulated in the shoots was broadly correlated with the relative phytotoxicity of methazole to the different species, except for young seedlings of V. persica which contained no DCPMU but were susceptible to methazole.     

Aspects of the selective phytotoxicity of methazole. II. Behaviour in plants following root exposure

The absorption, translocation and degradation of methazole were examined in onion, Stellaria media, Matricaria matricarioides and Veronica persica grown in culture solution. After a short period of initial rapid uptake, all four species absorbed herbicide and water in the same proportions. Translocation of herbicide to the shoots was directly proportional to transpiration, but the apparent solute concentration in the xylem was less than that in the external solution and varied between the species. A smaller percentage of the total absorbed herbicide was translocated to the shoot in V. persica, the most tolerant species. Methazole was relatively stable in M. matricariodes and was degraded slowly to 3-(3,4-dicnlorophenyl)-1-methylurea (DCPMU). It was degraded rapidly to DCPMU in the other three species and this accumulated in onion and S. media. In V. persica DCPMU was degraded further to 3-(3,4-dichlorophenyl) urea (DCPU). Methazole was not an active inhibitor of photosynthesis by isolated spinach chloroplasts. Both DCPMU and DCPU inhibited photosynthesis but DCPMU was 200-times more active than DCPU. Variations in the concentrations of DCPMU in the shoots of the different species largely accounted for the variations in their response to methazole applied pre-emergence.     

Metabolic fate of methazole in purple and yellow nutsedge

The mechanisms for the tolerance of purple nutsedge (Cyperus rotundus L.) and susceptibility of yellow nutsedge (Cyperus esculentus L.) to methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] were studied. Both species absorbed and translocated[¹⁴C]methazole and metabolites from nutrient solution; however, greater amounts of ¹⁴C per unit weight were detected in yellow than in purple nutsedge. Although intact plants and excised leaves of both species rapidly metabolized methazole to DCPMU [1-(3,4-dichlorophenyl)-3-methylurea], detoxification of DCPMU to DCPU [1-(3,4-dichlorophenyl) urea] occurred more slowly in yellow than in purple nutsedge. Compared to yellow nutsedge, a greater percentage of the radioactivity in purple nutsedge was recovered as polar products. Polar products were converted to the free forms of the parent herbicide and to phytotoxic DCPMU by proteolytic enzyme digestion. Based on the findings of this study, at least three mechanisms (differential absorption, metabolism, and formation of polar products) account for the differential tolerance of these two species to methazole.     

Metabolic fate of bioxone in cotton

The metabolic fate of the ¹⁴C-labeled herbicide, 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (bioxone), in cotton (Gossypium hirsutum L. “Acala 4-42-77”) was studied using thin-layer chromatography, autoradiography, and counting. Bioxone-¹⁴C was readily metabolized by cotton tissue to 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) and 1-(3,4-dichlorophenyl)urea (DCPU). Leaf discs metabolized bioxone-¹⁴C rapidly; 12 hr posttreatment, 65% of the ¹⁴C in methanol extracts was in forms other than intact herbicide. Excised leaves treated through the petiole with either heterocyclic ring-labeled or phenyl ring-labeled herbicide contained little bioxone-¹⁴C after 1 day; DCPMU was formed early then decreased with time. DCPU accounted for 55–70% of the ¹⁴C in excised leaves 3 days posttreatment. In intact plants treated via the roots, the herbicide was rapidly metabolized in the roots to DCPMU and DCPU; little or no intact herbicide was translocated to the leaves. Little radioactivity accumulated in the roots with time; the radioactivity in the leaves accounted for 80–90% of the methanol-soluble ¹⁴C 47 days posttreatment. Most of the ¹⁴C in the leaves was recovered as DCPU (50–60%) and unidentified polar metabolite(s) which remained at the origin of the thin-layer plates (30–40%). The percentage of radioactivity which remained in cotton residue after methanol extraction increased with time. Digestion of the plant residues with the proteolytic enzyme pronase indicated that some of the nonextractable ¹⁴C may be DCPMU and DCPU complexed with proteins. Similar metabolic patterns were noted after treatment with either heterocyclic ring-labeled or phenyl ring-labeled bioxone-¹⁴C. Generally, bioxone was metabolized to DCPMU which in turn was demethylated to DCPU. The herbicide and DCPMU were 20 times as toxic as DCPU to oat (Avena sativa L.), a susceptible species.     

The degradation of methazole in soil. I. Effects of soil type,soil temperature and soil moisture content

[¹⁴C]-Labelled methazole was incubated in six soils at 25°C and with soil moisture at field capacity. Under these conditions, methazole was unstable, the concentration declined following first-order kinetics with half-life values in the soils ranging from 2.3 to 5.0 days. The main degradation product was 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU) which was more stable than the parent compound. After about 160 days, DCPMU accounted for 30 to 45% of the initial methazole concentration. Degradation of methazole and DCPMU was affected by soil temperature and moisture content. With methazole, half-lives in one soil at field capacity moisture content and temperatures of 25, 15 and 5°C were 3.5, 8.7 and 31.1 days respectively. The half-life at 25°C was increased to 5.0 days at 50% of field capacity and 9.6 days at 25% of field capacity. A proportion of the initial radioactivity added to the soil could not be extracted and this proportion increased with time. After 160 days this unextractable radioactivity accounted for up to 70% of the amount applied.     

Prickly sida (Sida spinosa L.) and spurge (Euphorbia hyssopifolia L.) response to wide row and ultra narrow row cotton (Gossypium hirsutum L.) management systems

A 4 year field study was conducted from 1998 to 2001 to evaluate the response of prickly sida ( Sida spinosa L.) and hyssop spurge ( Euphorbia hyssopifolia L.) growing in either ultra narrow row (UNR) or wide row (WR) cotton ( Gossypium hirsutum L.) management systems. Weeds surviving pre- and postemergence herbicide treatments were harvested just prior to defoliation and the morphological characteristics were compared. Prickly sida growth was significantly reduced with regard to the number of main stem nodes, primary, secondary and tertiary branching, number of seed capsules produced and dry weight under UNR compared with WR. However, plant height was not affected by the management system. Spurge growth was significantly reduced with regard to branching and fresh weight but not height. These results show that UNR might suppress weed development by reducing vegetative and reproductive growth of prickly sida and vegetative growth of spurge. The reduction in seed and seed capsule production of prickly sida is likely to reduce its reproductive potential and also diminish the subsequent seed rain and soil seed bank reserves. Thus, a potential benefit of UNR cotton management systems might be to reduce the competitive ability of weeds and decrease seed production.     

Arrowleaf sida (Sida rhombifolia) and prickly sida (Sida spinosa): germination and emergence

Maximum arrowleaf sida (Sida rhombifolia L.) germination occurred at 35°C, whereas prickly sida (Sida spinosa L.) germinated to the same extent at 35 or 40°C. Arrowleaf sida germinated better than prickly sida at 20 and 25°C, but did not germinate at 40°C. Less than 50% of seed from both species were viable at 45°C after 21 days of exposure. Both species exhibited more than 75% germination at a range of pH from 5.0 to 8.0. Arrowleaf sida germinated to a greater extent than prickly sida from 0 to —800 kPa, and an osmotic stress of —200 kPa reduced prickly sida germination, whereas —400 kPa was necessary to reduce arrowleaf sida germination. Prickly sida emergence was optimal at a planting depth of 0.5 cm, and declined rapidly at deeper planting depths. However, arrowleaf sida emergence was equivalent at planting depths of 0.5–2.0 cm, with declining emergence below 2.0 cm. Neither species emerged from depths exceeding 5.0 cm. Light did not influence the germination of arrowleaf sida or prickly sida. Sida rhombifolia et Sida spinosa: germination et levee Le maximum du germination pour Sida rhombifolia L. a été atteint à 35°C tandis que Sida spinosa L. a germé de facon équivalente à 35 ou 40°C. S. rhombifolia a mieux germé que S. spinosaà 20 et 25°C, mais n'a pas germéà 40°C. Moins de 20% de graines des deux espèces étaient encore viables à 45°C après 21 jours dèxposition. Les deux especes ont germéà plus de 75% dans des niveaux de pH allant de 5 à 8. S. rhombifolia a mieux germe que S. spinosa de 0 à 800 kPa, et un stress osmotique de —200 kPa a réduit la germination de S. spinosa, tandis que —400 kPa ont été nécessaires pour réquire la germination de S. rhombifolia. La levée de S. spinosaétait optimale à une profondeur de semis de 0,5 cm, et décroissait rapidement à des profondeurs plus élevées. Cependant la levée de S. rhombifoliaétait équivalente pour des profondeurs de 0,5 à 2 cm, avec une baisse à partir de 2 cm. Aucune des deux espèces n'a levéà des profondeurs supérieurs à 5 cm. La lumière n'a pas d'influence sur la germination des 2 espèces. Keimung und Auflaufen der Sidafaserpflanze (Sida rhombifolia L.) und der Stacheligen Samtmalve (Sida spinosa L.) Die stärkste Keimung lag bei der Sidafaserpflanze (Sida rhombifolia L.) bei 35 °C vor, während Samen der Stacheligen Samtmalve (Sida spinosa L.) bei 35 oder 40 °C gleich gut keimten. Samen der Sidafaserpflanze keimten bei 20 und 25 °C besser als die der Stacheligen Samtmalve, keimten jedoch nicht bei 40 °C. Nach Lagerung bei 45 °C für 21 Tage waren die Samen beider Arten zu < 20% keimfähig. Bei pH-Werten zwischen 5 und 8 keimten beide Arten zu >75%. Bei osmotischen Drücken zwischen 0 und —800 kPa keimte die Sidafaserpflanze besser als die Stachelige Samtmalve, deren Keimung ab —200 kPa gehemmt wurde, wahrend bei der Sidafaserpflanze —400 kPa erforderlich waren, die Keimung zu verringern. Samen der Stacheligen Samtmalve keimten am besten in 0,5 cm Tiefe, in gröβerer Ablagetiefe schnell schlechter. Bei der Sidafaserpflanze jedoch waren Aussaattiefen zwischen 0,5 und 2,0 cm gleich gut, erst bei Tiefen unter 2 cm ging der Auflauf zurück. Aus Tiefen unter 5 cm keimte keine der beiden Arten. Durch Licht wurde die Keimung der beiden Sida Arten nicht beeinflußt.     

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.     

Characterization of herbicidal injury by acifluorfen-methyl in excised cucumber (Cucumis sativus L.) cotyledons

Initial signs of herbicidal injury by several diphenyl ether herbicides were monitored by following the efflux of ⁸⁶Rb⁺ from treated cucumber (Cucumis sativis L.) cotyledons after exposure to light (600 μE m^?2 sec^?1; measured as PAR, i.e., photosynthetically active radiation between 400 and 700 nm). This very sensitive, rapid, and quantitative bioassay proved quite useful in (a) a structure-activity correlations study of the diphenyl ether compounds investigated and (b) an examination of herbicidal characteristics. The following diphenyl ether herbicides were analyzed: acifluorfen, sodium 5-[2-chloro-4-(trifluormethyl)phenoxy]-2-nitrobenzoate; acifluorfen-methyl (MC-10108), methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate; bifenox, methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate; nitrofen, 2,4-dichlorophenyl p-nitrophenyl ether; nitrofluorfen, 2-chloro-1-(4-nitrophenoxy)-4-(trifluoromethyl)benzene; oxyfluorfen, 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene; MC-7783, potassium 5-(2,4-dichlorophenoxy)-2-nitrobenzoate; and MC-10982, ethyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate. Of the compounds investigated, acifluorfen-methyl (AFM) had the greatest degree of herbicidal activity. Cucumber cotyledons placed in high light (600 μE m^?2 sec^?1; PAR) with 10 nM AFM showed a significant increase in the efflux of ⁸⁶Rb⁺ within 2 to 4 hr. Light was required for herbicidal activity by AFM, and when treated cotyledons were returned to darkness, no further damage to the tissue occurred. By decreasing the quantity of light, the effect of the compound was delayed, although the magnitudes of the responses at the different intensities (600, 300, 150, and 75 μE m^?2 sec^?1; PAR) were nearly equal. By increasing the length of time of dark pretreatment with 1 μM AFM, ⁸⁶Rb⁺ efflux could be detected as early as 10 to 15 min after exposure to light (600 μE m^?2 sec^?1; PAR). Following light activation of AFM there was a simultaneous efflux of ⁸⁶Rb⁺, ³⁶Cl^?, ⁴⁵Ca²⁺, 3-O-methyl-[¹⁴C]glucose, and [¹⁴C]methylamine⁺. These data suggest the initial response to the herbicidal activity of AFM is expressed as a general increase in membrane permeability.     

Absorption and distribution of flurazole and acetochlor in grain sorghum

The site of uptake, absorption, and distribution of a safener, flurazole [2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylic acid, (phenylmethyl ester)], and a herbicide, acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-O-acetoluidide], in grain sorghum [Sorghum bicolor (L.) Moench “G-522 DR”] were investigated in laboratory and growth chamber studies. Acetochlor was absorbed through shoots while flurazole was taken up primarily by roots. Uptake of [¹⁴C]acetochlor into the plant was rapid, linear, and the ¹⁴C was concentrated in primary roots by 7 days. Absorption of [¹⁴C]flurazole by sorghum was immediate, leveled off at 4 days, and the ¹⁴C was concentrated in primary roots by 7 days. Absorption and distribution of either chemical were not affected by the presence of the other. Flurazole had a slight effect on acetochlor metabolism at 3 days, but by 6 days no differences were noted.     

The environmental fate of diuron under a conventional production regime in a sugarcane farm during the plant cane phase

BACKGROUND: Field studies of diuron and its metabolites 3-(3,4-dichlorophenyl)-1-methylurea (DCPMU), 3,4-dichlorophenylurea (DCPU) and 3,4-dichloroaniline (DCA) were conducted in a farm soil and in stream sediments in coastal Queensland, Australia. RESULTS: During a 38 week period after a 1.6 kg ha(-1) diuron application, 70-100% of detected compounds were within 0-15 cm of the farm soil, and 3-10% reached the 30-45 cm depth. First-order t(1/2) degradation averaged 49+/-0.9 days for the 0-15, 0-30 and 0-45 cm soil depths. Farm runoff was collected in the first 13-50 min of episodes lasting 55-90 min. Average concentrations of diuron, DCPU and DCPMU in runoff were 93, 30 and 83-825 microg L(-1) respectively. Their total loading in all runoff was >0.6% of applied diuron. Diuron and DCPMU concentrations in stream sediments were between 3-22 and 4-31 microg kg(-1) soil respectively. The DCPMU/diuron sediment ratio was >1. CONCLUSION: Retention of diuron and its metabolites in farm topsoil indicated their negligible potential for groundwater contamination. Minimal amounts of diuron and DCMPU escaped in farm runoff. This may entail a significant loading into the wider environment at annual amounts of application. The concentrations and ratio of diuron and DCPMU in stream sediments indicated that they had prolonged residence times and potential for accumulation in sediments. The higher ecotoxicity of DCPMU compared with diuron and the combined presence of both compounds in stream sediments suggest that together they would have a greater impact on sensitive aquatic species than as currently apportioned by assessments that are based upon diuron alone.     

The basis for the safening of clomazone by phorate insecticide in cotton and inhibitors of cytochrome P450s

Clomazone may be safely used in cotton to manage weeds when applied following treatments of the organophosphate insecticides phorate or disulfoton. The loss of chlorophyll and carotenoids with 6 days of 100 nM clomazone treatment of cotton seedlings was partially prevented with phorate in hydroponic solution in a rate-dependent manner. In a study to examine the timing of safening from a one-day clomazone (100 nM) treatment, maximum safening was achieved when phorate (50 μM) was applied the same day as clomazone. Phorate decreased metabolism of ¹⁴C-clomazone to polar metabolites in excised cotton shoots and shoots of intact cotton plants. Microsomal studies of corn shoots showed an NADPH-dependent/cytochrome P450 reaction was inhibited by phorate. Additional studies with corn microsomes, corn seedlings and cotton seedlings supported the basis of clomazone safening is the inhibition of toxic clomazone metabolism by P450 inhibitors.     

Degradation of the herbicide benzoylprop-ethyl in soil

The degradation of [¹⁴C] benzoyl prop ethyl (SUFFIX,^a ethyl N-benzoyl-N-(3,4-dichlorophenyl)-2-aminopropionate) in four soils has been studied under laboratory conditions. The major degradation product of benzoylprop ethyl at up to 4 months after treatment was its corresponding carboxylic acid (II). On further storage this compound became firmly bound to soil before it underwent a slow debenzoylation process which led to the formation of a number of products including N-3,4-dichlorophenylalanine (IV), benzoic acid, 3,4-dichloroaniline (DCA), which was mainly present complexed with humic acids, and other polar products. Although these polar products were not identified, they were probably degradation products of DCA, since they were also formed when DCA was added to soil. No 3,3′,4,4′-tetrachloroazobenzene (TCAB) was detected in any of the soils at limits of detectability ranging from 0.01-0.001 parts/million. Since N-3,4-dichlorophenylalanine (IV) and 3,4-dichloroaniline were transient degradation products of benzoylprop ethyl, the metabolism in soil of radiolabelled samples of these compounds was also studied. In these laboratory experiments the persistence of the herbicide increased as the organic matter content of the soil increased and the time for depletion of half of the applied benzoylprop ethyl varied from 1 week in sandy loam and clay loam soils to 12 weeks in a peat soil.     

Localizing the action of two thiadiazolyl herbicidal derivatives

Enzymatically isolated leaf cells from navy beans (Phaseolus vulgaris L., cv. “Tuscola”) were used to study the effect of buthidazole (3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone) and tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea) on photosynthesis, protein, ribonucleic acid (RNA), and lipid synthesis. The incorporation of NaH¹⁴CO₃, [¹⁴C]leucine, [¹⁴C]uracil, and [¹⁴C]acetic acid as substrates for the respective metabolic process was measured. 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 very sensitive to both buthidazole and tebuthiuron and was inhibited in 30 min by 0.1 μM concentrations. RNA and lipid syntheses were inhibited 50 and 87%, respectively, by buthidazole and 42 and 64%, respectively, by tebuthiuron after 120 min at 100 μM concentration. Protein synthesis was not affected by any herbicide at any concentration or any exposure time period. The inhibitory effects of buthidazole and tebuthiuron on RNA and lipid syntheses may be involved in the ultimate herbicidal action of these herbicidal chemicals.     

Metabolism of the insecticide SD 8280, 2-chloro-1-(2,4-dichlorophenyl)vinyl dimethyl phosphate,following its application to rice

The metabolism of the insecticide SD 8280 [2-chloro-1-(2,4-dichlorophenyl)vinyl dimethyl phosphate] in rice plants has been examined. When rice seedlings were treated with [¹⁴C]-SD 8280 the major metabolite was 1-(2,4-dichlorophenyl)ethanol which was present mainly conjugated with plant carbohydrates. This compound was also the major metabolite present in grain and straw from rice treated with [¹⁴C]-SD 8280 and grown to maturity under paddy conditions both in the glasshouse and in an outdoor enclosure. Other metabolites detected in the mature plants included 2-chloro-1-(2,4-dichlorophenyl)vinyl methyl hydrogen phosphate and 2,4-dichloro-benzoic acid, both of which occurred in free and conjugated forms. Paddy water was sampled at intervals after the application of [¹⁴C]-SD 8280 and the total residue in the water fell from initial levels of 0.28–1.1 μg/ml (expressed as SD 8280 equivalent) immediately after treatment to <0.01 μg/ml after 2–3 weeks. The total residues in the soil from these experiments were low and did not exceed 0.20 mg/kg (SD 8280 equivalents) through the 0–15 cm profile.     

Studies on the mode of action of asulam,aminotriazole and glyphosate in Equisetum arvense L. (field horsetail). II: The metabolism of [14C]asulam, [14C]aminotriazole and [14C]glyphosate

The metabolism of [¹⁴C]asulam (methyl 4-aminophenylsulphonylcarbamate), [¹⁴C] aminotriazole (1H-1,2,4-triazol-3-ylamine) and [¹⁴C]glyphosate (N-(phosphonomethyl)glycine) were assessed in Equisetum arvense L. (field horsetail). Following application of the test herbicides (4mg?0.3 °Ci herbicide/shoot) to the shoots of 2-year-old pot-grown plants, the total recovery of ¹⁴C-label after 1 week and 8 weeks was high for all three herbicides (>80-0% of applied radioactivity). Asulam was persistent (>69-7% of recovered radioactivity) in both shoots and rhizomes. Sulphanilamide, a hydrolysis product of asulam, accounted for the remainder of the recovered radioactivity. Aminotriazole showed evidence of conjugation in shoots and rhizomes. The principal ¹⁴C-labelled component in shoots was composed of high proportions of aminotriazole (>76-3%) together with the metabolites: X (ninhydrin positive), β-(3-amino-1,2,4-triazolyl-1-)α-alanine, Y (diazotization positive) and various unidentified compounds. Rhizomes generally contained lower proportions of intact aminotriazole (>59.4%) together with the metabolites X,Y and unidentified compounds. The proportion of aminotriazole did not decrease with time in shoots or rhizomes; however, the ratio of metabolite X: Y moved in favour of Y as the interval after treatment increased. Glyphosate was extensively metabolised in shoots and rhizomes to yield aminomethylphosphonic acid (AMPA) and various unidentified compounds. Differential metabolism appears to be one of the factors which may govern the persistence and toxicity of the test herbicides in E. arvense.     

Penetration and metabolism of topically applied permethrin and cypermethrin in pyrethroid-tolerant Wiseana cervinata larvae

The penetration, excretion, and metabolism of topically applied [¹⁴C]permethrin and [¹⁴C]cypermethrin have been examined in larvae of the porina moth Wiseana cervinata to determine the factors which affect body levels of unchanged pyrethroids. Metabolism was by hydrolysis and to a lesser extent oxidation and the primary metabolites were quickly conjugated to water-soluble products. Little excretion occurred and body levels of unchanged pyrethroids were dependent on the interaction of penetration and metabolism. cis-Cypermethrin was more resistant to metabolism than trans-cypermethrin and cis- and trans-permethrin. trans-Permethrin most readily penetrated into larvae. The body levels of unchanged permethrin were enhanced by pretreatment of larvae with the metabolic inhibitors carbaryl or piperonyl butoxide. Tolerance of the pasture pest porina to the synthetic pyrethroids is discussed in relation to these findings.     

Oxidative degradation of chlortoluron,propiconazole, and metalaxyl in suspension cultures of various crop plants

The metabolism of chlortoluron, (N′-(3-chloro-4-methylphenyl)-N,N-dimethylurea), propiconazole (1-[2-(2′,4′-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl]-1H-1,2,4-triazole), and metalaxyl (dl-N-(2,6-dimethylphenyl)-N-(2′-methoxyacetyl) alanine methyl ester) was investigated in suspension cultures of crop species for which differences in metabolism had been demonstrated at the intact plant level. Uptake and metabolism of chlortoluron by cultures of Italian rye-grass (Lolium multiflorum) was slow, the metabolites detected (42% of applied radioactivity after 13 days) being products of ring methyl oxidation and N-monodealkylation reactions. In sharp contrast, metabolism in a cotton (Gossypium hirsutum) suspension culture was extremely fast (72% after 4 hr) and was attributed to extensive N-didealkylation in addition to rapid ring methyl oxidation. This rate of metabolism also implied a very rapid uptake of chlortoluron by the cotton culture. ¹⁴C-labelled propiconazole became rapidly associated with cells of wheat (Triticum aestivum) and rice (Oryza sativa) following treatment of suspension cultures. Uptake was initially more rapid in the rice culture (36% of applied radioactivity after 8 h compared to 19% for wheat) which, together with a slower rate of metabolism, resulted in more unchanged propiconazole being associated with rice cells. On a parts-per-million basis these results indicated an apparent 10-fold accumulation of propiconazole in rice cells compared to 5-fold in the wheat culture. Propiconazole metabolite patterns were similar in cultures of both species and indicated side-chain hydroxylation as the principal pathway. Uptake of metalaxyl was slow in suspension cultures of both lettuce and potato (≅ 20% after 17 days). Subsequent metabolism was also slow but appeared to be limited by the poor rate of uptake. Both cultures were found to be similarly versatile with respect to metabolic attack on metalaxyl, which included ring methyl hydroxylation, aryl hydroxylation, ester cleavage, ether cleavage (O-dealkylation), and N-dealkylation (side-chain cleavage), the hydroxylation reactions being quatitatively the more important. The results for all three pesticides are compared to those obtained previously from studies with intact plants of the same species.     

The degradation of the herbicide benzoylprop ethyl on the foliage of cereal seedlings

The breakdown of the herbicide benzoylprop ethyl [SUFFIX, ethyl N-benzoyl-N-(3,4-dichlorophenyl)-2-aminopropionate] has been examined in wheat, oat, and barley seedlings after application of ¹⁴C-labeled herbicide to the foliage.Within 15 days of the application the route and rate of the breakdown were similar in the plants of all three species. Some of the herbicide was present in the plants in a complexed form which could be extracted from the plant with organic solvents and converted back into the herbicide on treatment with hot acid. Evidence was obtained for hydrolysis of the herbicide in the plant to give its des-ethyl analog which conjugated with plant sugars. There was some evidence for a small degree of degradation of benzoylprop ethyl by debenzoylation to give products which also conjugated or complexed.There was no evidence for the formation of 3,4-dichloroaniline in the plants.