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.     

Influence of water stress on absorption, translocation and phytotoxicity of fenoxaprop-ethyl and imazamethabenz-methyl in Avena fatua

The influence of water stress on the absorption and translocation of ¹⁴C-labelled fenoxapropethyl and imazamthabenz-methyl in Avena fatua L. (wild oat) was studied. The phytoioxicity to A. fatua of both herbicides with a droplet application was also examined under water stress conditions. The absorption of both fenoxaproethyl and imazamethabenz-methyl was reduced by waler stress when the plants were harvested within 24 h after herbicide application. Up to 48 h after the application, the translocation out of the treated lamina of both herbicides, based on percentage of applied ¹⁴C. was reduced under water stress conditions. When havested 96 h after herbicide application, however, water stress no longer significantly affeaed the absorption and translocation of either herbicide. When the herbicides were applied as individual droplets, water stress reduced the phytotoxicity of fenoxaprop-ethyl but not that of imazamethabenz-methyl. It is concluded that the changes in herbieide absorption and translocation may not be the major physiological processes associated with differential whole-plant response oi A faiua to fenoxaprop-ethyl and imazamefhabenz-methyl under water stress.     

Foliar absorption and translocation of nicosulfuron and rimsulfuron in five annual weed species

Ambrosia artemisüfolia L. (common ragweed) and Digitaria ischaemum Schreb. (smooth crabgrass) are not controlled by nicosulfuron and rimsulfuron at the highest recommended application rates, whereas Panicum miliaceum L. (wild proso millet), Amaranthus retroflexus L. (redroot pigweed) and Avena fatua L. (wild oat) are susceptible. The foliar absorption and translocation of ¹⁴C-nicosulfuron and ¹⁴C-rimsulf uron were studied in these weed species up to 48 h after treatment (HAT). Differences in herbicide uptake and translocation were not correlated with the species susceptibility. By 48 HAT, more than 50% of both herbicides remained on the treated leaf surface. Foliar absorption of rimsulfuron was greater than that of nicosulfuron in A. retroflexus, P. miliaceum and A. artemisüfolia. Most of the absorbed herbicide remained in the treated leaf of each weed species. Export of ¹⁴C–nicosulfuron ranged from 28 to 54% of that absorbed, in contrast to 15 to 39% for ¹⁴C–rimsulfuron. The absorption and translocation rates of both herbicides were highest within the initial 6 HAT, and decreased thereafter. Both herbicides showed approximately the same distribution pattern within each weed species.     

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.     

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.     

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.     

Effects of two surfactant series on the absorption and translocation of 14C-glyphosate in sicklepod and prickly sida

The weed species, prickly sida (Sida spinosa L.) and sicklepod (Senna obtusifolia L.), were treated with ¹⁴C-glyphosate alone and formulated with different polyethlylane oxide (PEO) surfactants in tallow amine ethoxylate and non-ionic alkoxylate series to determine the amount of ¹⁴C-glyphosate absorption and translocation. The surface tension, contact angle, and ¹⁴C-glyphosate distribution were significantly affected by both the presence of different waxes on the plants and by the addition of surfactants to the glyphosate. The surface and contact angle values of the surfactants, with and without glyphosate, showed a significant increase as the PEO number increased in both surfactant series. A higher absorption of the ¹⁴C-glyphosate was recorded for S. spinosa compared with S. obtusifolia. The absorption and translocation of the ¹⁴C-glyphosate increased with the increase in the PEO number of tallow amine ethoxylate. In the case of the non-ionic alkoxylate surfactant series, an increase in the absorption of ¹⁴C-glyphosate was recorded when the surface tension and contact angle values decreased. There was no significant difference in the translocation values obtained in the two species after the addition of the surfactants. The amount of ¹⁴C-glyphosate absorbed by the treated leaf was significantly higher in the case of S. spinosa compared with S. obtusifolia. A linear relationship was observed with the physical properties, ¹⁴C absorption, and the efficacy of glyphosate with the addition of the non-ionic alkoxylate surfactant series. The percentage control was higher with the higher PEO surfactant in the tallow amine ethoxylate surfactant series and with the lower PEO surfactant in the non-ionic alkoxylate surfactant series as the two series are chemically different.     

Effects of formulation with different adjuvants on foliar uptake of difenzoquat and 2,4-D: model experiments with wild oat and field bean

The effect of different adjuvants on the foliar uptake of difenzoquat methyl sulfate and sodium 2,4-D was studied in wild oat and field bean plants growing under controlled environmental conditions. The ¹⁴C-herbicides were applied to leaves as c. 0–2-μl droplets, usually containing 0.5 g 1^?1 active ingredient, plus adjuvants in the range 0.05–5 g 1^?1. The addition of non-ionic polyoxyethylene surfactants to solutions of both herbicides could induce considerable foliar uptake. Aliphatic C₁₃C₁₃ alcohol surfactants generally improved uptake more than nonylphenol surfactants when used at equivalent concentrations and ethylene oxide (EO) contents. The surfactant threshold for enhancement of difenzoquat uptake in wild oat was very low (0.05 g 1^?1), whilst that in field bean was much higher (>0.5 g 1^?1). For 2,4-D, surfactants at >0–5 g 1^?1 were needed to produce substantial increases in its uptake into both species. Although surfactants of low EO content (5–6) were less efficient at promoting difenzoquat uptake than those of higher EO content (10–20), particularly in wild oat, there was little dependence on surfactant EO content for enhancement of 2,4-D uptake. Adjuvants with humectant properties also promoted penetration of difenzoquat, but less so than alcohol or nonylphenol surfactants. For formulations of both ¹⁴C-herbicides translocation was directly related to the quantity of radiolabel that had penetrated the leaf tissue. Effets de la formulation avec différents adjuvants sur l'absorption foliaire du difenzoquat et du 2,4-D: modeles experimentaux sur la folle avoine et le haricot L'influence de differents adjuvants sur l'absorption foliaire du difenzoquat methyl sulfate et du 2,4 D sodium a eétéétudiée chez la folle avoine et le haricot, cultivés sous des conditions environnementales contrôlées. Les herbicides marquees au ¹⁴C ont ete appliquées aux feuilles sous forme de gouttelettes de 0,2 μl contenant 0,5 g 1^?1 de matière active, avec en plus des adjuvants de 0,05 à 5 g ^?1. L'adjonction de surfactants polyoxyethylénes non ioniques aux solutions des deux herbicides pourrait induire un absorption foliaire importante. Les surfactants d'alcools aliphatiques C₁₃/C₁₅ ont généralement augmenté la pénétration mieux que les surfactants de type nonylphénol utilises à une concentration équivalente et que les oxydes d'éthylènes (EO). Le seuil de surfactant pour l'amélioration de l'absorption de difenzoquat sur folle avoine était très bas (0,05 g 1^?1) tandis que sur haricot, il était beaucoup plus éievé (> 0,5 g 1^?1). Pour le 2,4 D, des surfactants à une dose de >0,5 g 1^?1 sont nécessaires pour produire une amelioration de son absorption chez les deux espéces. Bien que les surfactants à faible teneur en EO (5–6) fussent moins efficace pour favoriser l'absorption du difenzoquat que ceux a forte teneur (10–20), spécialement pour la folle avoine, il y avait une petite dépendance sur la teneur en EO pour l'amélioration de l'absorption du 2,4 D. Les adjuvants avec des propriétés d'humectation ont favorisé la pénétration du difenzoquat, mais moins que les surfactants alcool ou nonylphenol. Pour les formulations des deux herbicides marqués au ¹⁴C, le transport était directement reliéà la quantité de molécule marquée ayant pénétrée dans le tissu foliaire. Wirkung verschiedener Netzmittel auf die Blattaufnahme von Difenzoquat und 2,4-D am Beispiel von Flug-Hafer und Ackerbohne Der Einfluß verschiedener Zusatzstoffe auf die Blattaufnahme von Difenzoquat und 2,4-D-Na- Salz wurde an Flug-Hafer- und Ackerbohnen-Pflanzen unter kontroUierten Bedingungen untersucht. Die ¹⁴C-Herbizide wurden auf die Blatter mit etwa 0,2 μl großen Tröpfchen einer Lösung mit 0,5 g 1^?1 AS und 0,05 bis 5 g 1^?1 des Zusatzstoffs ausgebracht. Durch Zugabe von nichtionischen Polyoxyethylen-Netzmittein zu den Lösungen der beiden Herbizide konnte die Blattaufnahme erheblich gesteigert werden. Aliphatische C₁₃C₁₅-Alkohol-Netzmittel förderten die Aufnahme mehr als Nonylphenol-Netzmittel, wenn sie mit equivalenten Konzentrationen und Ethylenoxid-(EO)Gehalten ausgebracht wurden. Die Schwelle für die Steigerung der Difenzoquat-Aufnahme durch Netzmittel lag bei Flug-Hafer sehr niedrig (0,05 g 1^?1), bei der Ackerbohne vielhöher (>0,5 g 1^?1). Bei 2,4-D wurden bei beiden Arten zur deutlichen Förderung der Aufnahme Netzmittelkonzentrationen von >0,5 g 1^?1 benötigt. Obwohl Netzmittel mit niedrigem EO-Gehalt (5–6) die Difenzoquat-Aufnahme weniger förderten als solche mit höherem Gehalt (10–20). besonders bei Flug-Hafer, ergab sich für die Förderung der 2,4-D-Aufnahme kaum eine Abhängigkeit vom EO-Gehalt des Netzmittels. Additive mit feuchtigkeitshaltenden Eigenschaften förderten auch die Aufnahme von Difenzoquat, aber weniger als alkoholische oder nonylphenolische Netzmittel. Die Translokation der Mischungen der beiden ¹⁴C-Herbizide stand in direktem Verhäitnis zur Radioaktivitätsmenge, die in das Blattgewebe aufgenommen wurde.     

The effectiveness of old and new strategies for the long‐term control of Pteridium aquilinum,an 8‐year test

There is a need for management strategies to control dominant perennial weeds and restore seminatural communities. We compared the effects of five weed control treatments on dense Pteridium aquilinum relative to an untreated experimental control over an 8‐year period with the aim of restoring acid grassland. The weed control treatments tested were as follows: cutting and bruising, both twice and thrice annually, and herbicide treatment (asulam in year 1 followed by annual spot retreatment of all emergent fronds). Pteridium aquilinum performance and plant species composition were monitored. Data were analysed using Bayesian mixed‐effect models and multivariate techniques. Cutting twice and thrice yearly and the asulam treatment all reduced frond density to zero; both bruising treatments were ineffective. The plant communities in the cut and asulam‐treated plots showed differences from the untreated and bruised plots; the asulam‐treated plots contained more ruderal species and the cut plots were more typical of acid grassland. Acid grassland recovery was fastest in the asulam‐treated plots, but the cut plots caught up after approximately 5 years. There were two important conclusions. First, an intractable weed like P. aquilinum can be eradicated and a vegetation more suited for grazing can be achieved by the continuous application of some treatments over many years. Here, success was achieved by cutting twice/thrice annually, or by a single asulam application followed by annual spot spraying of all emergent fronds for 8 years. Second, bruising, a treatment favoured by some conservation organisations, did not work and cannot be recommended. The use of long‐term, continuously applied treatments might be considered for all perennial weeds with large underground root/rhizome systems.     

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

The uptake and translocation of [¹⁴C]asulam (methyl 4-aminophenyl-sulphonylcarbamate), [¹⁴C]aminotriazole (1-H-1,2,4-triazol-3-ylamine) and [¹⁴C]glyphosate (N-(phosphonomethyl)glycine) were assessed in Equisetum arvense L. (field horsetail), a weed of mainly horticultural situations. Under controlled-environment conditions, 21°C day/18°C night and 70% r. h., the test herbicides were applied to 2-month-old and 2-year-old plants. Seven days following the application of 0.07-0.09 °Ci (1.14mg) of the test herbicides to young E. arvense, the accumulation of ¹⁴C-label (as percentage of applied radioactivity) in the treated shoots, untreated apical and basal shoots was as follows: [¹⁴C]asulam, 13.2, 0.18 and 1.02%; [¹⁴C] aminotriazole, 67.2, 3.65 and 1-91%; [¹⁴C]glyphosate, 35.9, 0.06 and 0.11%. The equivalent mean values for the accumulation of ¹⁴C-label in 2-year-old E. arvense were [¹⁴C]asulam, 12.0, 1-15 and 1.74%; [¹⁴C]aminotriazole, 58.6, 9.44 and 4.12%; [¹⁴C]glyphosate, 33.1, 0.79 and 2.32%. In the latter experiment, test plants received 0.25-0.30 °Ci (4mg) of herbicide, they were assessed after a 14-day period and the experiment was carried out at 3-week intervals between 2 June and 25 August on outdoor-grown plants. Irrespective of test herbicide or time of application, very low levels of ¹⁴C-label accumulated in the rhizome system. Only 0.2% of the applied radioactivity was recovered in 2-year-old plants and 0.4% in 2-month-old plants. In the young plants [¹⁴C]asulam accumulated greater amounts and concentrations of ¹⁴C-label in the rhizome apices and nodes than [¹⁴C]aminotriazole or [¹⁴C]glyphosate treatments. Inadequate control of E. arvense under field conditions may be due to limited basipetal translocation and accumulation of the test herbicides in the rhizome apices and nodes.     

Studies on the mode of action of diflufenican in selected crop and weed species: Basis of selectivity of pre- and early post-emergence applications

Diflufenican, a pre- and early post-emergence herbicide, was found to be highly active against a wide range of weeds at application rates of 50–250 g ha-1. Studies on the mode of selectivity with [14C]diflufenican have demonstrated that selectivity between cereal crops and selected weed species is primarily due to differential uptake and indirectly to translocation; ‘depth protection’ appears to be the major reason for selectivity of soil-applied diflufenican.     

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.     

A review of the effects of humidity, humectants, and surfactant composition on the absorption and efficacy of highly water-soluble herbicides

It is well known that environmental conditions have an important influence on herbicide efficacy. In particular, the effect of humidity on herbicide uptake has been attributed to changes in cuticle hydration and droplet drying. As early as the 1950s, it was hypothesized that humectants such as glycerol would enhance herbicide uptake by not letting droplets dry, thus maintaining the herbicide in solution, and hence making it available for uptake. Shortly thereafter, evidence was found to support this hypothesis and humectants were used successfully in warm, dry areas to increase herbicide efficacy. However, by the mid-1980s, there was little use of humectants as research on humectants gave way to investigations on the effect of ethylene oxide (EO) content on surfactant performance to improve herbicide uptake and efficacy. While ethoxylated surfactants effectively increase the uptake of both lipophilic and hydrophilic herbicides, the suggestion that long EO chains have humectant properties is misleading, since the studies that led to this suggestion were performed at high humidity, which would prevent rapid droplet drying. Furthermore, current evidence suggests that highly water-soluble, ionic herbicides may be more sensitive to low humidity and rapid drop drying than lipophilic herbicides. Therefore, an overview is presented on the interaction of water-soluble herbicides with surfactants, the cuticle, and humidity, with particular emphasis on the impact of low humidity and humectants on herbicide uptake. It was found that when one focuses on research performed at low humidity the importance of humectants emerges, which is not in keeping with what is now commonly accepted.     

Influence of some nonionic surfactants on water sorption by isolated tomato fruit cuticles in relation to cuticular penetration of glyphosate

The effects of several nonionic surfactants on [¹⁴C]glyphosate mono(isopropylammonium) diffusion across isolated tomato fruit cuticles (Lycopersicon esculentum Mill.) were compared under controlled atmospheric conditions (25°C; 65% R.H.) using a model system consisting of 1-μl droplets applied to isolated cuticles on agar blocks. Rates of diffusion for glyphosate (10 g acid equivalent litre^?1 in the applied solution) and overall amounts recovered in underlying agar blocks were influenced by the ethylene oxide (EO) chain length for a homologous nonylphenol surfactant series (10 g litre^?1). Glyphosate uptake increased with EO content, reaching an optimum at a mean of 17 EO, then decreasing below control values for surfactants with 40 EO. There was a strong influence of the hydrophobe on glyphosate penetration for different surfactants with similar mean EO content (10 EO). The primary aliphatic amine enhanced penetration the most, followed by the nonylphenol while the aliphatic alcohol showed no improvement on glyphosate transfer across cuticles. Water soprtion was greatly enhanced by a primary aliphatic amine (10 EO) and by a nonylphenol (17 EO). The aliphatic alcohol (10 EO) and a shorter-chained nonylphenol (4 EO) did not significantly enhance water sorption. Comparison of water sorption with glyphosate diffusion across cuticles suggests a strong relationship between the two. Change in solution pH over a limited range had no significant effect. Promotion of cuticular hydration by surfactants may thus play an important role in the enhancement of foliar uptake of water-soluble herbicides such as glyphosate.     

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

Penetration of bean (Vicia faba var. Maris Bead) foliage by asulam was found to be affected differently by different surfactants. Some anionic and non-ionic surfactants brought about a significant increase compared with the aqueous control, others were similar to the aqueous control and one caused a significant reduction. High humidity increased asulam uptake and the effect was still further enhanced in the presence of Tween 20. High humidity was also found to influence asulam penetration in the presence of glycerol. With urea, uptake was greater under high humidity conditions and in the presence of Tween 20. A similar enhancement of penetration was found with potassium ethyl xanthate at lower concentrations (0–0.20%) in the presence of Tween 20. On the other hand, reduced uptake resulted at higher concentrations (0.40–1.00%). Tributyl phosphate brought about an increase in penetration at concentrations greater than 0.75%. However, both potassium ethyl xanthate and tributyl phosphate were shown to damage the leaf surface.     

Spray retention, foliar penetration, translocation and selectivity of asulam in wild oats and flax

Summary: Résumé: Zusammenfassung The spray retention, foliar penetration and translocation of asulam [methyl (4 aminobenzenculphonyl) carbamate] by wild oats (Avena fatua L.) (Susceptible) and flax (Linum usitatissimum L.)(Tolerant) were examined in an attempt to elucidate the nature of differential sensitivity. Wild oat plants retained about four times as much spray solution of a commercial formulation of asulam as did flux. Penetration into flax was much more rapid than into wild oats. Added surfactant and high relative humidity greatly enhanced the penetration of the herbicide into wild oats. An increase in temperature from 10 to 30° C resulted in a large increase in penetration into both species. After foliar application of ¹⁴C-asulam the radioactivity was distributed throughout the wild oat plants. But the translocation in flax was very limited. Here most of it remained in the treated leaf, probably as a result of contact injury caused by the chemical No detectable qualitative or quantitative differences in the metabolism of asulam in the two species were found. Our studies suggest that spray retention, foliar penetration and translocation all play an important role in the selectivity of asulam between wild oats and flax. Rétention'de la pulvérisation, pénélration foliaire, migration el selectivity de I'asulamt chez la folle-avoine et Ie lin La rëtention de la pulvérisation, la pénétration foliaire et la migration de I'asusulame (4 aminobenzënesulfonyl carbamate de méthyle) not étéétudJiees chez la folle avoine (Avfna fatua L.) (sensible)ct chez le lin (Linum usitalissimum L) (resistant) pour tenter d'ëlucider la nature de la difference de scnsibilité. LES plantes de folle-avoine ont retenu quatre fois plus que le lin de la pulvérisation d'une formulation commercial d'asulame. La pénétration dans Ie lin a été beaucoup plus rapide que dans la folle-avoine. L'addition d'un agent de surface et one humidité relative êlevêe ont grandement favorisê la pênetration de I'herbicide dans la folle-avoine one élévation de la temperature de 10 à 30° C a provoqué one import ante augmenta tion de la pênêtration dans les deux espèces. Après one application foliaire d'asulame marqué au ¹⁴C. la radioactivité a été rêpartie dans l'ensemble de la plante chez la folle-avoine. mais la migration chez le lin a êtê três limitêe. La plus grande panie de cette radioactivitê est restêe dans la feuille traitèe. probablement en raison des damages provoquês par le contact duproduit. ll n'a pasêtêdecelê de differences, ni qualitatives. niquantitatives. Dans)le mêtabolisme de l'asulame chez les deux espêces. Nos recherches suggèrent que la retention de la pulvêrisation, la pénétration fotiaire et la migration jouent un röle important dans la sélectivité de l'asulame entre la folle-avoine et le lin. Spritzmitelrterenrntion, Blmprnetlration, Tronslokation and Selekrivitär von Asulam hei Flughafer and Flachs Spritzmittelretention. Blat penetration and Translokation von Asuiam [Methyl-l-aminobenzolsulfonyl)-carbamat] bei Flughafer (Avina fatua L.)empfindlich) and Flachs (Limum usiiaiis imum L.)(tolerant) wurden untersucht mit dem ziel. Aufklärung über die Ursache der unter Mhiedlichen Emptindlichkeit zu erhalten Flughaferpflanzen hielten etwa vicnnai so vicl Spritzmittellösung ciner handclsüblichen Asulamformulierung zurück wie Flachs. Die Penetration bei Flachs erfolgte vicl schnelier als bei Flughafer. Der Zusatz von oberflächenaktiven Stoffen and hohe Luftfeuchtigkeit erhöhten die Penetration des Herbizids bei Flughafer beträchtlish. Tcmperaturerhöhung von 10 auf 30°C führte bei beiden Pflanzenarten zu einer starken Zunahme der Penetration. Nach Blattapplikation von ¹⁴C-Asu lam war bei Flughafer die Radioaktivität über die gesamte Pflanze verleilt; bei Flachs dagegen fand nur eine sehr beschränkteTranslokation statt. Hier verblieb die meiste Radio aktivität im behandelten Blatt. was wahrscheinlich auf eine Schädigung durch Kontaktwirkung des Mittels zURÜCKZU führenist. Qualitative oder quantitative Unlerschiede im Metabolismus von Asulam in den beiden Pflanzen konnten nicht gefunden werden. Unscre Untersuchungen lassen vermuten. dass Spritzmittelretention. Biattpenetration and Translokation gemeinsam für die Selektivität von Asulam zwisehen Flughafer und Flachs eine wichiige Rolle spielen.     

Studies of the mechanism of action of asulam in plants. Part I: Antagonistic interaction of asulam and 4-aminobenzoic acid

Studies have been carried out on the herbicidal action of asulam [methyl (4-aminophenylsulphonyl)carbamate] and sulphanilamide, alone or in association either with 4-aminobenzoic acid (4ABA) or 4, 6-diamino-1-(3, 4-dichlorophenyl)-1, 2-dihydro-2, 2-dimethyl-1,3,5-triazine (DCDT). The soaking of wheat seeds (Triticum estivum L.) for 12 h at 30°C in asulam and DCDT in a 10:1 ratio doubled the inhibition of root growth produced by soaking in asulam alone; the addition of 4ABA partially reversed the activity of asulam. Foliar applications of a mixture of asulam + DCDT (1.1 + 0.55 kg ha^?1) markedly increased the activity of asulam in susceptible wheat, wild oat (Avena fatua L.), tolerant flax (Linum usitatissimum L.), and in Stellaria media L. The activity of asulam at 1.1 kg ha^?1 was reversed by 4ABA at 2.2 kg ha^?1 by about 50% in wheat and wild oat, 82% in flax and 100% in S. media. The results indicate that asulam and sulphanilamide act by similar mechanisms in apparently inhibiting the biosynthesis of folic acid.     

Increased foliar activity of clodinafop‐propargyl and/or tribenuron‐methyl by surfactants and their synergistic action on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis)

Surfactants can improve postemergence herbicide efficacy and reduce the amount of herbicide required to obtain weed control. The effect of surfactants on the efficacy of herbicides is complicated and depends on the interaction among the plant, surfactant, and herbicide. The effects of surfactants on the efficacy of clodinafop‐propargyl and/or tribenuron‐methyl on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis) under greenhouse conditions were investigated. In addition, the surface tension of aqueous solutions of the surfactants and surfactants + herbicides was determined. Significantly lower surface tension values were obtained with the aqueous solutions of citofrigate (Citogate plus Frigate) alone and with the herbicides used in this study. The citofrigate surfactant lead to the greatest enhancement of clodinafop‐propargyl and/or tribenuron‐methyl efficacy and the effect was species‐dependent. The efficacy of clodinafop‐propargyl and/or tribenuron‐methyl in the presence of surfactants in controlling wild oat was higher than for wild mustard. The foliar activity of the tested herbicides rose with increasing surfactant concentrations. The tank mixture of clodinafop‐propargyl and tribenuron‐methyl showed a synergistic effect in controlling wild oat and wild mustard. The synergistic effect in controlling wild mustard was greater than for wild oat.     

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.     

Studies on the selectivity of alloxydim-sodium in plants

Alloxydim-sodium, methyl 3-[1-(allyloxyimino)butyl]-4-hydroxy-6,6-dimethyl-2-oxocyclohex-3-enecarboxylate sodium salt, is a selective herbicide which controls grass weeds in a wide range of broad-leaf crops. Spray retention, tested at two growth stages, was generally greater for the broad-leaf crops (cotton, sugarbeet, flax, beans and peas) than for wild oat (Avena fatua L.), blackgrass (Alopecurus myosuroides Huds), barley and couch grass [Agropyron repens (L.) Beauv.], and did not contribute to selectivity between susceptible and tolerant species. Broad-leaf crops tolerated 2820 g alloxydim-sodium ha^?1, three times the recommended rate used to control annual grasses. Differential uptake and translocation were not factors contributing to selectivity. In wild oat, blackgrass and sugarbeet, uptake and translocation of ¹⁴C continued during a period of 14 days after treatment with [¹⁴C]alloxydim-sodium. Translocation in susceptible and tolerant species was predominately symplastic. Over 40% of the applied ¹⁴C was eliminated from treated wild oat, blackgrass and sugarbeet plants within 7 days, due to degradation and volatilisation. A greater proportion of the methanol-soluble radioactivity extracted from leaves and roots was present as water-soluble polar metabolites in sugarbeet, than in wild oats, 7 days after treatment. The proportion of unaltered alloxydim in the organo-soluble fraction of a methanol extract was greater in wild oat than in sugarbeet. Differential metabolism appears to be one of the factors contributing to alloxydim-sodium selectivity between sugarbeet and wild oat.