Effect of non-ionic nonylphenol surfactants on surface physicochemical properties, uptake and distribution of asulam and diflufenican

The effect of non-ionic nonylphenol (NP) surfactants containing 4–14 ethylene oxide (EO) molecules on the distribution of asulam and diflufenican was investigated in Pteridium aquilinum L. Kuhn and Avena fatua L. The distribution of the herbicides was dependent on the EO content and concentration of surfactant and differed between plant species and herbicide. The surface properties of contact angle, droplet diameter and surface tension were examined. For solutions of asulam, the greatest reductions in contact angle, surface tension and greatest droplet diameter were obtained with surfactants of EO 6.5–10 (at 0.001–0.1%). For solutions of diflufenican, these responses were greatest when applied with surfactant of EO 4. Surfactants of EO 6.5–10 increased the uptake and translocation of [¹⁴C]asulam in P. aquilinum, particularly at surfactant concentrations of 0.01 % and 0.1 %. All surfactants increased uptake of [¹⁴C]asulam in A. fatua with no significant effects of surfactant EO number or concentration. For both species, there was a positive correlation between the optimum surface characteristics of the herbicide droplets and the uptake of asulam. With diflufenican, greatest uptake and translocation by mature frond tissue of P. aquilinum occurred at the highest concentration of surfactant EO 4; in A. fatua, however, uptake and translocation were not significantly affected by any of the surfactants.     

Studies on the mode of action of asulam in bracken (Pteridium aquilinum L. Kuhn) I. Absorption and translocation of [14C]asulam

Studies of the absorption and translocation of foliage-applied ring-labelled [¹⁴C]asulam [methyl (4-aminobenzenesulphonyl) carbamate] were carried out using glasshouse and field-grown bracken plants. Translocation of ¹⁴C from the treated frond was primarily according to a 'source to sink’pattern with intense accumulation of radioactivity in the metabolically active sinks viz. rhizome apices, frond buds, root tips and young frond tissue. In the case of field bracken, translocation and distribution of ¹⁴C was extensive in the rhizome system, accumulation occurring in the active as well as dormant buds situated on the non-frond-bearing and storage rhizome branches. Treatment of fully expanded fronds with 100μl of [¹⁴C]asulam (1 mg, 1.0–1.5 μCi) as 2 μl droplets resulted in a rapid initial uptake during the first week, followed by progressive entry and distribution with time. Basipetal translocation to the rhizome system was positively correlated with total uptake. High humidity (95%) and high temperature (30°C) stimulated uptake and subsequent basipetal translocation to a considerable degree. Uptake was greater through the stomatal-bearing abaxial than through the adaxial cuticle. Incorporation of a surfactant (Tergitol-7, 0.1%) increased penetration by up to 30%. Uptake declined markedly as the frond aged, while translocation was predominantly acropetal in young treated fronds, becoming exclusively basipetal when the fronds matured. Optimum uptake and maximum distribution of [¹⁴C]asulam in the rhizome and its associated buds was achieved when treatments were applied to almost fully expanded fronds. The translocated ¹⁴C (asulam and possibly some of its metabolites) showed a considerable degree of persistence in the rhizome system, 8% of the applied activity still remaining in the rhizome 40 weeks after treatment.     

Penetration of bean leaves by aminotriazole as influenced by adjuvants and humidity

Penetration of bean leaves (Phaseolus vulgaris var. Canadian Wonder) by aminotriazole (3-amino-1,2,4-triazole) was greatly enhanced under high humidity conditions (ca 10% in 17 h at the low humidity level (LHL) compared with ca 80% in 2 h at the high humidity level (HHL)). The addition of polyoxyethylene 20 sorbitan monolaurate (polysorbate 20) to the spray fluid increased penetration on all occasions at the LHL. The increase obtained was found to be dependent on the concentration of polysorbate 20. The inclusion of polysorbate 20 at the HHL resulted in an increase in aminotriazole penetration at low polysorbate 20 concentrations 0.2–12.8 g/litre and a non-significant decrease over the aqueous control at a concentration of 40 g/litre. With additions of glycerol to the spray fluid, aminotriazole penetration was increased on all occasions at the LHL while at the HHL no concentration of glycerol was found to enhance penetration. The addition of polysorbate 20 (< 0.1 to 40 g/litre) to a spray solution containing glycerol (0.3 ml/litre) enhanced penetration at the HHL compared with the aqueous and glycerol controls. A polysorbate 20 plus glycerol combination (6.4 g+0.6 ml/litre) gave the same order of penetration (98.4 and 94.0%) at the HHL and LHL respectively. In both cases penetration exceeded that obtained with the corresponding polysorbate 20 and glycerol controls. Some of the practical implications of these findings are discussed.     

Penetration of bracken fronds by asulam as influenced by the addition of surfactant to the spray solution and by pH

Asulam (methyl(4-aminobenzenesulphonyl)carbamate) does not penetrate rapidly on foliar application to bracken (Pteridium aquilinum). Its performance is therefore erratic if rain follows immediately after spraying. The addition of the surfactant polyoxyethylene sorbitan monolaurate (Tween 20) increased spray retention and doubled penetration of asulam by the bracken frond. Concentrations of Tween 20 greater than 01 % (w/v) gave no further increase in penetration and pH had no effect. Pénéetration de l'asulame dans les frondes de fougiré: influence de l'addition d'un mouillant a la bouillie herbicide et du pH L'asulame (méthyl(4-aminobenzinsulfonyl)carbamate) ne pénètre pas rapidement lorsqu'il est appliqué par voie foliaire sur la fougére (Pteridium aquitinum). En conséquence, son efficacité est irrégulière s'il plcut immédiatement apres le traitement. L'addition d'un mouillant, le Tween 20 ou monolaurate de polyoxyéthylène sorbitol a augmenté la rétention de la pulvérisation et a doublé la pénétration de l'asulame dans les frondes de fougères. Les concentrations de Tween 20 supérieures à 0,1 % (pds/vol) n'ont pas augmenté la pénétration et le pH s'est montré sans effet. Der Einfluss von Netzmittetzusatz und pH auf die Penetration von Asulam in Wedel des Adterfarns Asulam (N-(4-Amino-benzolsulfonyl)-carbaminsäure-methyl-ester) dringt in Adlerfarn (Pteridium aquilinum) bei Blattapplikation nicht schnell ein. Deshalb ist seine Wirkung unzuver-lässig, wenn es unmittelbar nach der Spritzung regnet. Der Zusatz des Netzmittels Polyoxyäthylensorbitanmonolaurat (Tween 20) erhöhte die Retention der Spritzbrühe und verdoppelte die Penetration von Asulam in die Adlerfarnwedel. Höhere Konzentrationen von Tween 20 als 0,1 % (Gew./Vol.) steigerten die Penetration nicht und das pH spielte keine Rolle.     

Effects of some nonionic polyoxyethylene surfactants on uptake of ethirimol and diclobutrazol from suspension formulations applied to wheat leaves

The influence of a number of commercial nonionic polyoxyethylene surfactants on the foliar penetration and movement of two systemic fungicides, ethirimol and diclobutrazol, was studied in outdoor-grown wheat plants at different growth stages and post-treatment temperatures in two consecutive growing seasons. Both fungicides were applied as ca 0·2 μl droplets of aqueous suspension formulations containing 0·5 g litre^?1 of ¹⁴C-labelled active ingredient; surfactants were added to these suspensions at concentrations ranging from 0·2-10 g litre^?1. To achieve optimum uptake of each fungicide the use of surfactants with different physicochemical properties was required. For diclobutrazol, a lipophilic compound, uptake of radiolabel was best with surfactants of low mean molar ethylene oxide (E) content (5-6) but it was necessary to use concentrations of ca 5 g litre^?1 to attain this. The surfactant threshold concentration for uptake enhancement of radiolabel from ethirimol formulations (< 2 g litre^?1) was much lower than that for diclobutrazol but surfactants with E contents > 10 induced the greatest amount of uptake. For both fungicides, surfactants with an aliphatic alcohol hydrophobe were generally more efficient in promoting their uptake than those with a nonylphenol moiety. The sorbitan-based surfactant ‘Tween 20’ proved to be an effective adjuvant only for the ethirimol formulation; the uptake enhancing properties of the block copolymer ‘Synperonic PE/F68’ were weak. Uptake performance could not be related to the spreading properties of the respective formulations on the wheat leaf surface or to differences in solubilisation of the two fungicides by the surfactants. Although surfactants could substantially increase the amount of acropetal transport of radiolabel from both fungicides, none of those tested specifically promoted it; a constant proportion of the radioactive dose absorbed by a treated leaf was usually exported away from the site of application. The results are discussed in the light of current theories about the mode of action of surfactants as spray adjuvants.     

Selectivity factors relative to asulam for Senecio jacobaea L. control in Medicago sativa L. I. Retention,uptake and translocation*

Senecio jacobaea L. and Medicago sativa L. plants grown in a glasshouse were treated with foliar applications of aqueous solutions of asulam. Retention on foliage, uptake and translocation were measured in both species. Retention was greater in S. jacobaea than in M. sativa when no surfactant was added and similar when surfactant was added. Addition of surfactant modified spray distribution and increased asulam uptake in M. saliva but did not in S. jacobaea. S. jacobaea translocated over twice as much asulam from the treated area as M. sativa. These data suggest that surfactant should not be added for maximum selectivity. Differences in species response to asulam treatments are partially, but not entirely, explained by differences in retention, uptake and translocation.     

Uptake of aminotriazole from humectant-surfactant combinations and the influence of humidity

Uptake of aminotriazole (3-amino-1,2,4-triazole) by bean leaves (Phaseolus vulgaris var. Canadian Wonder) was not greatly influenced by the addition to the spray solution of dimethylformamide (DMF), ethylene glycol and polypropylene glycol 400 (PPG 400) over the concentration range 1.0–50.0 ml litre^?1. However, the addition of polyoxyethylene 20 sorbitan monolaurate (polysorbate 20) (0.2–1.0 g litre^?1) to spray solutions of the above additives and glycerol (5.0 ml litre^?1; except for DMF, 50.0 ml litre^?1) substantially increased uptake to 80–100% in all cases at 50 ± 10% relative humidity (r.h.). Similar penetration figures were recorded when a range of polysorbate surfactants (polysorbate 20, 40, 60, 80 and 85; 0.2 g litre^?1) were applied to spray solutions containing either dimethyl sulphoxide (DMSO) or glycerol (5.0 ml litre^?1). Humidity was found to have a critical effect upon the humectant-surfactant combinations tested, i.e. DMSO + polysorbate 20, ethylene glycol+ polysorbate 20 and PPG + 400-polysorbate 20 (5.0 ml litre^?1+0.2 g litre^?1). With DMSO + polysorbate 20 the following uptake figures were recorded: < 30% r.h., 3.1 %; 45 ± 10% r.h., 86.8%; 55–65% r.h., 48.2 % and 100% r.h., 0.3%. Similar trends were recorded with all three humectant-surfactant combinations. Further studies revealed that the adverse effect of humidity on DMSO-polysorbate mixtures could be at least overcome partially by regulating the DMSO concentration.     

Selectivity factors relative to asulam for Senecio jacobaea L. control in Medicago sativa L. II. Metabolism*

Metabolism of ¹⁴C asulam applied with surfactant was studied in Senecio Jacobaea L. and Medicago saliva L. Plants were harvested 48, 96 and 144 h after treatment and extracted with acetone. The aqueous residue of the acetone extract was partitioned with ethyl acetate and the ¹⁴C activity in the ethyl-acetate phase, the aqueous phase and the plant residue was determined. A significant amount of ¹⁴C activity was not extracted by acetone from either species. This amount increased with time in M. sativa but remained relatively constant in S. jacobaea. More ¹⁴C activity was found in the aqueous phase than in the ethyl-acetate phase in M. sativa while the reverse was true in S. jacobaea. Significantly lower amounts of free asulam were identified in M. sativa than in S. jacnbaea. Still, results of these and previous studies on retention, uptake and translocation do not completely account for differences in sensitivity found in greenhouse and field applications. Other possible explanations for selectivity are discussed.     

Uptake and translocation of [14C]asulam and [14C]bromacil by roots of maize and bean plants

The uptake and translocation of ¹⁴C-ring-labeled asulam (methylsulfanilcarbamate) and bromacil (5-bromo-3-sec-butyl-6-methyluracil), were compared after root application to maize (Zea mays L.) and bean (Phaseolus vulgaris L.). Autoradiographs showed the distribution of bromacil throughout these and other plant species, and the retention of asulam in the roots. The recovery of both compounds in quantitative radioassays was between 90 and 100%. The absorption of bromacil and asulam was rather similar. Absorption of bromacil increased up to 20% of the applied dose in bean plants after 2 days of exposure, and up to 11% in maize plants after 4 days. Absorption of asulam in bean plants was 22% of the applied dose after 2 days, and 8% in maize plants after 4 days. The pattern of distribution of bromacil and asulam was completely different. After 4 h of exposure of the roots about half of the absorbed bromacil had accumulated in the shoots, while two-thirds or more was translocated to the shoots after exposure periods of 1 to 4 days. Not more than one-eighth of the absorbed asulam was found in the shoots. In consequence, the bromacil content in the transpiration stream relative to that in the ambient solution was much higher than that of asulam. The leakage of asulam from bean and maize roots into herbicide-free nutrient solution was lower than that of bromacil. The reasons for these differences are not yet clear. There was only some metabolism of asulam in maize, but not in bean plants. No metabolites of bromacil were detected in the two plant species.     

The movement of paraquat as influenced by the partition coefficient of surfactants between water and leaf wax

“Lissapol” NX and “Lubrol” L, used to improve the uptake of paraquat into plants were found in earlier work to reduce its movement. Several series of surfactants with widely varying solubilities in water were partitioned between cabbage wax and water. A marked correlation was found between the effect of surfactants on the movement of paraquat and the amount of surfactant partitioning into the wax. It is concluded that although surfactants increase the uptake of paraquat into leaves, this increase is offset by reduced movement following penetration of surfactants into leaf tissue. Surfactant partition into wax reduces the degree of penetration, but there is no evidence how surfactants in leaf tissue reduce movement.     

Cuticular uptake of xenobiotics into living plants. Part 2: influence of the xenobiotic dose on the uptake of bentazone, epoxiconazole and pyraclostrobin, applied in the presence of various surfactants, into Chenopodium album, Sinapis alba and Triticum aestivum leaves

This study has determined the uptake of three pesticides, applied as commercial or model formulations in the presence of a wide range of surfactants, into the leaves of three plant species (bentazone into Chenopodium album L. and Sinapis alba L., epoxiconazole and pyraclostrobin into Triticum aestivum L.). The results have confirmed previous findings that the initial dose (nmol mm(-2)) of xenobiotic applied to plant foliage is a strong, positive determinant of uptake. This held true for all the pesticide formulations studied, although surfactant concentration was found to have an effect. The lower surfactant concentrations studied showed an inferior relationship between the amount of xenobiotic applied and uptake. High molecular mass surfactants also produced much lower uptake than expected from the dose uptake equations in specific situations.     

Contributions of stomatal infiltration and cuticular penetration to enhancements of foliar uptake by surfactants

Radiolabelled deoxyglucose (DOG) and glyphosate were used to investigate the effects of certain non-ionic surfactants on the kinetics of foliar uptake in three species. ‘Silwet L-77’ (5 g litre^?1), an organosilicone surfactant, enabled spray solutions to infiltrate stomata, providing uptake of DOG into Vicia bean (50%), oat (35%) and wheat (20%) within 10 min of application. ‘Silwet Y-12301’, another organosilicone, also induced stomatal infiltration but to a lesser extent; unlike L-77, this was attenuated by partial stomatal closure. A third organosilicone, ‘Silwet L-7607’, and two conventional surfactants, ‘Triton X-45’ (OP5) and ‘Agral 90’ (NP9), did not induce stomatal infiltration. The effective minimum concentration of L-77 required to enable infiltration of stomata was 2 g litre^?1. The uptake of glyphosate into bean did not differ from that of DOG but the ‘Roundup’ formulation of glyphosate partially antagonised the infiltration provided by L-77. Addition of surfactants did not increase the rate of cuticular penetration of DOG into bean but total uptake was increased, except by NP9, either via infiltration (L-77 and Y-12301) or by extending the period during which penetration occurred (L-7607 and OP5). The surfactants had a variable effect on rates of penetration of DOG into wheat and oat. In general, foliar uptake followed an exponential timecourse which was largely complete within 6 h and only rarely approached 100% of the applied chemical. The stomatal infiltration provided by L-77 caused an increase in translocation of DOG in bean.     

Studies on a new group of biodegradable surfactants for glyphosate

The effectiveness of a homologous series of biodegradable rapeseed oil derivatives (triglyceride ethoxylates; Agnique RSO series containing an average of 5, 10, 30 and 60 units of ethylene oxide (EO) as adjuvants for foliage-applied, water-soluble, systemic active ingredients was evaluated employing glyphosate as an example. Previous experiments had revealed that the surfactants used are not phytotoxic at concentrations ranging from 1 to 10 g litre-1. The experiments were performed using Phaseolus vulgaris L and nine selected weed species, grown in a growth chamber at 25/20 (+/- 2) degrees C day/night temperature and 40/70 (+/- 10)% relative humidity. The surfactants were evaluated for enhancement of spray retention, and foliar penetration biological efficacy of glyphosate. Glyphosate was applied at a concentration of 43 mM. The surfactants were added at concentrations of 1 g litre-1. The commercial glyphosate 360 g AE litre-1 SL Roundup Ultra and unformulated glyphosate served as references. The surfactants used improved spray retention, foliar penetration and biological efficacy. Some of the formulations were comparable to the performance of Roundup Ultra in the aspects evaluated; some were even more effective in enhancing spray liquid retention and promoting glyphosate phytotoxicity in several plant species. In these studies Agnique RSO 60 generally was most effective.     

Effect of additives in aqueous formulation on the foliar uptake of dimethomorph by cucumbers

BACKGROUND: The efficacy enhancement of dimethomorph formulation by several adjuvants is thought to be through increased foliar uptake. In order to identify the most effective adjuvants, the adjuvancy of 36 additives was examined in aqueous formulations in relation to the absorption of dimethomorph by cucumber leaves. RESULTS: Polyethylene glycol monohexadecyl ethers with ethylene oxide (EO) contents of between 7 and 20, polyethylene glycol monooctadecyl ethers with EO contents of between 10 and 20 and polyethylene glycol monooctadecenyl ethers with EO contents of between 6 and 20 were effective adjuvants for promoting dimethomorph uptake from both aqueous acetone solutions and aqueous wettable powder (WP) suspensions into cucumber leaves. Polyethylene glycol monododecyl ethers with EO contents of between 7 and 9 were effective in promoting dimethomorph uptake from aqueous WP suspensions but less effective relative to the other adjuvants tested with aqueous acetone solutions. Foliar uptake of dimethomorph was also facilitated by the addition of methyl hexadecanoate, methyl octadecenoate and methyl octadecadienoate. CONCLUSIONS: Although the foliar uptake of dimethomorph from both aqueous WP suspensions and aqueous acetone solutions was greatest in the presence of fatty alcohol ethoxylates generally having a C₁₆ or C₁₈ lipophile, uptake from aqueous surfactant–acetone solutions was, on average, 7.6‐fold greater than that from aqueous WP suspensions containing surfactant. Copyright © 2009 Society of Chemical Industry     

Uptake and movement of paraquat in cocksfoot and wheat as influenced by surfactants

Surfactants are used to increase the efficiency of herbicide formulations mainly because they wet out leaf surfaces, thereby stabilising and increasing the contact area of droplets on the surface. Herbicide penetration through the cuticle may also be facilitated. The work described eliminates effects on wetting and contact area in order to study the effect of surfactants on the penetration and movement of paraquat in cocksfoot. Surfactants were various types of alcohols and amine oxides condensed with 2 to 30 moles of ethylene oxide used at 0.1 to 0.5%. An adult leaf of cocksfoot (Dactylis glomerata) was immersed briefly to constant area in paraquat solutions containing surfactant and uptake and movement of paraquat is recorded. Uptake was little affected by differences in surfactant structure except where surface activity was low and solutions failed to wet out the leaf surface. Percentage movement with 0.5% surfactant was often less than that with 0.1% and a high ethylene oxide content also reduced percentage movement. Paraquat activity was influenced by both the degree of uptake and movement, but movement was the greater influence. Amine oxide surfactants reduced movement less than those based on alcohols. The action of surfactants is discussed in terms of a hydrophobic/hydrophilic balance in the surfactant molecule.     

Some physicochemical factors influencing foliar uptake enhancement of glyphosatemono(isopropylammonium) by polyoxyethylene surfactants

Structure-concentration–foliar uptake enhancement relationships between commercial polyoxyethylene primary aliphatic alcohol (A), nonylphenol (NP), primary aliphatic amine (AM) surfactants and the herbicide glyphosatemono(isopropylammonium) were studied in experiments with wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants growing under controlled-environment conditions. Candidate surfactants had mean molar ethylene oxide (EO) contents ranging from 5 to 20 and were added at concentrations varying from 0·2 to 10 g litre^?-1 to [¹⁴C]glyphosate formulations in acetone–water. Rates and total amounts of herbicide uptake from c. 0·2–μl droplet applications of formulations to leaves were influenced by surfactant EO content, surfactant hydrophobe composition, surfactant concentration, glyphosate concentration and plant species, in a complex manner. Surfactant effects were most pronounced at 0·5 g acid equivalent (a.e.) glyphosate litre^?-1 where, for both target species, surfactants of high EO content (15–20) were most effective at enhancing herbicide uptake: surfactants of lower EO content (5–10) frequently reduced, or failed to improve, glyphosate absorption. Whereas, at optimal EO content, AM surfactants caused greatest uptake enhancement on wheat, A surfactants gave the best overall performance on field bean; NP surfactants were generally the least efficient class of adjuvants on both species. Threshold concentrations of surfactants needed to increase glyphosate uptake were much higher in field bean than wheat (c. 2 g litre^?-1 and < 1 g litre^?-1, respectively); less herbicide was taken up by both species at high AM surfactant concentrations. At 5 and 10 g a.e. glyphosate litre^?-1, there were substantial increases in herbicide absorption and surfactant addition could cause effects on uptake that were different from those observed at lower herbicide doses. In particular, the influence of EO content on glyphosate uptake was now much less marked in both species, especially with AM surfactants. The fundamental importance of glyphosate concentration for its uptake was further emphasised by experiments using formulations with constant a.i./surfactant weight ratios. Any increased foliar penetration resulting from inclusion of surfactants in 0·5 g litre^?-1 [¹⁴C]glyphosate formulations gave concomitant increases in the amounts of radiolabel that were translocated away from the site of application. At these low herbicide doses, translocation of absorbed [¹⁴C]glyphosate in wheat was c. twice that in field bean; surfactant addition to the formulation did not increase the proportion transported in wheat but substantially enhanced it in field bean.     

Studies on octylphenoxy surfactants. Part 2: Effects on foliar uptake and translocation

The effects of octylphenol (OP) and four of its ethoxylated derivatives on uptake into, and distribution within, maize leaf of 2-deoxy-glucose (2D-glucose), atrazine and o, p′-DDT are reported. The surfactants and OP (2 g litre^?1 in aqueous acetone) increased the uptake, at both 1.5 and 24 h, of the three model compounds (applied at 1 g litre^?1) having water solubilities in the g, mg and μg litre^?1 ranges. The uptake of 2D-glucose was positively correlated with the hygroscopicity of the surfactants. The uptake of DDT and atrazine increased with the uptake of the surfactants, being inversely related to their hydrophile:lipophile balance (HLB). Uptake of 2D-glucose and atrazine was enhanced at high humidity, the relative enhancement for atrazine increasing with increasing ethylene oxide (EO) content of the surfactants. A significant proportion of the atrazine and DDT entering the leaf was recovered from the epicuticular wax, the amount of atrazine recovered from the wax increasing with the EO content of the surfactants. The proportion of the surfactants taken up which was recovered from the epicuticular wax was minimal at an EO content of 12.5–16 mole equivalents. The appearance of the deposits on the leaf surface differed markedly among the surfactants, with similar trends for all three chemicals and without visible evidence for infiltration of the stomatal pores. The total quantities of glucose and atrazine translocated were increased by all surfactants but that of DDT was not, despite increases in uptake of up to 7.5-fold. Relative translocation (export from treated region of leaf as a percentage of chemical penetrating beyond the epicuticular wax) was reduced in all cases in the presence of surfactant. Up to 30% of the applied [¹⁴C]chemicals was not recovered from the treated leaf after 24 h. The reduced recovery of 2D-glucose, but not that of atrazine and DDT, was largely attributable to movement out of the treated leaf, with approximately 70% of the chemical taken up being translocated basipetally. Loss of atrazine and DDT was a result of volatilisation. There was no evidence that either [14C]2 D-glucose or [¹⁴C]atrazine was metabolised to [¹⁴C]carbon dioxide.     

Studies on the mode of action of asulam in bracken (Pteridium aquilinum L. Kuhn) II. Biochemical activity in the rhizome buds

The effect of asulam (methyl (4-aminobenzenesulphonyl) carbamate) on the synthesis of RNA and protein was investigated in bracken sporeling plants and excised rhizome bud tissue. Foliage application of asulam (4.4 kg/ha) reduced the RNA levels in frond buds and young fronds within 3 days, while protein levels were significantly reduced after 14 days. A significant reduction in respiratory activity of buds was observed after 2 weeks, the level of inhibition being 54% after 8 weeks. During a 3-h incubation period, O₂ uptake by excised bud issue was stimulated by 5 and 10 ppm asulam and inhibited by higher concentrations; ₃₂P uptake was inhibited at all concentrations. Asulam (5 ppm and above) inhibited bud growth and reduced RNA and protein levels in incubated buds (20 h at 30°C), and the incorporation of [₁₄C]orotic acid into RNA and [₁₄C]leucine into protein. Reduction of RNA levels and inhibition of [₁₄C]ladenine incorporation into RNA in buds occurred entirely in the ribosomal and supernatant fractions of the cellular extract. Inhibition of RNA synthesis by asulam (50 ppm) as measured by [₁₄C] orotic acid incorporation into RNA was completely antagonized by CEPA (3-chloroethylphosphonic acid) (50 ppm) and partially by 2,4-D (2,4-dichlorophenoxyacetic acid) (50 ppm) and GA (Gibberellic acid) (50 ppm). These results suggest that the interference of asulam with RNA and protein synthesis at the metabolically active sinks (rhizome buds) could be one of its major mechanisms of action in bracken.     

Asulam mixtures for weed control in flax

Five field experiments were conducted from 1972 to 1975 to evaluate weed control in flax (Linum usitatissimum L.) using post-emergence treatments of asulam [methyl (4-aminobenzenesulphonyl) carbamatel alone and in combination with other herbicides. The ¹⁴C-asulam absorption by leaf segments and roots of glasshouse grown wild oats (Avena fatua L.) was also investigated. Asulam at 1.12 kg/ha gave good wild oat control and acceptable control of green foxtail (Setaria viridis (L.) Beauv.). However, wild oat control was poorer when asulam was combined with other herbicides: on a 3-year average, as compared with asulam alone at equal rates, the asulam+MCPA mixture resulted in a greater antagonism and a significant 6% reduction in flax seed yield, whereas the asulam+bromoxynil/MCPA mixture gave the least antagonistic effect, improved broadleaf weed control and increased yield by 13%. In mixtures, the potassium salt of MCPA was more compatible with asulam for weed control than the amine form. Both leaf segments and roots of wild oats absorbed and distributed less ¹⁴C-asulam from solutions containing MCPA than from those containing bromoxynil or bromoxynil/MCPA.     

Relative solubilities of bifenox and 1-naphthylacetic acid (NAA) in plant cuticles and in selected pure or aqueous glycol additives

The driving force for foliar penetration is the product of the partition coefficient (K) between the cuticle and the formulation residue, and the concentration of the active ingredient in the spray residue. Ethylene glycols and polyethylene glycols (PEGs) are often contained in commercial formulations, because they are good solvents and not toxic. Since they are humectants, the water content of the formulation residue varies with humidity of the air. At 25°C and 65% relative humidity PEG 400 contains about 50% water. The partition coefficients for the lipophilic herbicide, bifenox, increased with increasing water content of the ethylene glycols and PEGs, such that log K was a linear function of the mass fraction of water or PEG. The K value was about 0·5 for the system cuticle/pure PEG and 27500 for the system cuticle/water. When PEG contained 50% water, K was only 110. Partition coefficients of bifenox between cuticle and ‘Tween’ 80 depended also on humidity, having values of 0·75 in cuticle/pure ‘Tween’ 80 and 29·1 when ‘Tween’ 80 contained 50% water. With 1-naphthylacetic acid (NAA), which is a weak acid, partition coefficients also depended on water content of PEG 400, but a maximum curve was obtained. The maximum partition coefficient (211) was observed with a mixture of 30% PEG 400 and 70% water, which corresponded to a humidity of 88%. We suggest that this is due to an effect of PEG 400 on the ionisation of NAA. Our data demonstrate that partition coefficients are affected by humidity, because solubilities of lipophilic compounds and weak acids in PEG/water mixtures vary greatly with the water content. This in turn affects driving forces, mainly by the effect of humidity on partition coefficient. With non-ionisable lipophilic compounds, partition coefficients, driving forces and rates of foliar uptake therefore increase with increasing humidity. © 1998 SCI