Promotion of stomatal infiltration of glyphosate by an organosilicone surfactant reduces the critical rainfall period

The addition of the organosilicone surfactant ‘Silwet L77’ at 1-5 ml litre^?1 to formulated glyphosate gave complete surface wetting on application to the adaxial leaf surface of perennial ryegrass (Lolium perenne L.). The wetting characteristics of the solution were associated with rapid foliar uptake and near maximal uptake in 3 h compared to greater than 5 h in the absence of ‘Silwet L77’. Evidence is presented showing that solutions containing ‘Silwet L77’ rapidly infiltrate stomata. Rapid uptake did not occur after application to the astomatous abaxial surface of perennial ryegrass leaves. The rapid rate of glyphosate uptake reduced the critical rainfall period to 2 h or less, compared to up to 10 h in the absence of ‘Silwet L77’. The use of ‘Silwet L77’ has major practical implications for the use of glyphosate in regions with unpredictable rainfall or high rainfall frequency.     

几种有机硅助剂对草甘膦在单子叶植物体内吸收、转移和分布的影响

采用14C-草甘膦同位素标记法研究了4种有机硅助剂Silwet L-77、Silwet 800 、Freeway 和Boost 在体积分数0.1%用量下对草甘膦在黑麦草( Lolium perenne L. cv. Grasslands Greenstone)体内吸收、转移和分布的影响。结果表明:与单用草甘膦相比，4 种助剂的加入显著地降低了草甘膦在黑麦草体内的吸收和转移量，助剂之间无显著性差异。 处理后24和72 h测定，草甘膦主要分布在幼嫩组织中，其次是根部，在老叶片中的转移量最 少。无论转移量高低，草甘膦在植物体内的分布总是表现为地上部的比例高于地下部。有机 硅助剂对草甘膦在各组织中的分布比例没有影响。     

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 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.     

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.     

Optimizing foliar activity of glyphosate on Bidens frondosa and Panicum maximum with different adjuvant types

The influence of non-ionic (X-77) and organosilicone (L-77) adjuvants and of methylated seed oil (MSO) on the uptake, translocation and efficacy of glyphosate was investigated in Bidens frondosa L. and Panicum maximum Jacq. In addition, the physicochemical properties of adjuvants and adjuvant + glyphosate aqueous solutions were determined. Significantly lower surface tension and contact angle values were obtained with aqueous solutions of L-77 alone and with glyphosate. Over a 48-h time course, it was observed that >50% of applied ¹⁴C-glyphosate was absorbed within 15 min in B. frondosa with L-77. At 6 h and thereafter, ¹⁴C glyphosate absorption was significantly higher with MSO compared with X-77 in B. frondosa . In P. maximum , uptake and translocation of ¹⁴C-glyphosate + adjuvant were increased in general up to 48 h after treatment application, except with L-77, which showed no improvement in uptake – instead there was a significant reduction compared with no treatment with L-77. This indicated its antagonistic effect on this grass species. The lower values of ¹⁴C-glyphosate in P. maximum also confirmed that adjuvant effects were species specific. In the efficacy studies, glyphosate formulated with L-77 achieved significantly higher control of B. frondosa , while there was no control of P. maximum with this treatment. This confirmed antagonism in glyphosate absorption into P. maximum by L-77. Furthermore, significantly higher control of tested plants was recorded with MSO in comparison to X-77, which confirms the solubilizing or humectant nature of MSO.     

Insecticidal activity of surfactants and oils against silverleaf whitefly (Bemisia argentifolii) nymphs (Homoptera: Aleyrodidae) on collards and tomato

The insecticidal activities of four surfactants (Cide‐kick, Silwet L‐77, M‐Pede and APSA‐80), a dishwashing detergent (New Day), a mineral oil (Sunspray oil), a cotton seed oil and a vegetable oil, alone or in combination, were tested against nymphs of Bemisia argentifolii Bellows & Perring on collards and tomato. Silwet L‐77 was more effective (>95% mortality) than Cide‐Kick or APSA‐80 at rates from 0.25–1.00 g AI litre⁻¹ but caused severe phytotoxicity to tender tomato leaves at all but the lowest rate. New Day dish detergent at 2.0 ml litre⁻¹ caused mortality (95%) comparable to M‐Pede insecticide soap at 10‐fold greater concentration. A New Day ingredient, cocamide DEA, was considerably more active than the other ingredients or the commercial mixture. Additional surfactants added to Sunspray oil increased efficacy in some treatments, but not others. Toxic responses of 2nd‐ and 3rd‐ instar whiteflies to vegetable oil and cotton seed oil at 5.0 and 10.0 ml litre⁻¹ plus 0.4 g AI litre⁻¹ APSA‐80 ranged from 22.1 to 79.9% and 66.3–88.7% mortality, respectively. Whitefly mortality was greater on tomato than on collard in six of seven instances when differences between host plants were significant. Our results indicate that the these surfactants and oils have good potential for controlling B argentifolii. © 2000 Society of Chemical Industry     

Effects of herbicide mixtures and additives on Rhododendron ponticum

The possibility of increasing the activity of glyphosate, imazapyr, sulfonylurea herbicides and triclopyr against Rhododendron ponticum L. was investigated using container-grown plants. Glyphosate, imazapyr and triclopyr alone and metsulfuron-methyl with added surfactant were all phytotoxic, imazapyr and triclopyr being the most effective at the doses used. Thifensulfuron-methyl and tribenuron-methyl with ‘Mixture B’ were ineffective. The surfactants ‘Mixture B’ and ‘Silwet L77’ consistently increased the activity of imazapyr and metsulfuron-methyl. Mixtures of the herbicides did not lead to synergistic activity, and mixing imazapyr and triclopyr depressed the activity of each component. There was some enhancement of activity on R. ponticum when imazapyr and metsulfuron-methyl were applied sequentially, 48 h apart. Effets de mélanges d'herbicides et d'adjuvants au Rhododendron ponticum La possibilité d'accroître l'activité du glyphosate, de l'imazapyr, des sulfonylurées et du triclopyr contre Rhododendron ponticum a étéétudiée en utilisant des plantes cultivées en containers. Le glyphosate, l'imazapyr et le triclopyr seuls et le metsulfuron-methyl additionné d'un surfactant ont tous été phytotoxiques: l'imazapyr et le triclopyr étant les plus efficaces aux doses utilisées. Le thifensulfuron-méthyl et le tribenuron-methyl avec ‘Mixture B’ ont été inefficaces. Les surfactants ‘Mixture B’ et‘Silwet L 77’ ont considérablement augmenté l'activité de l'imazapyr et metsulfuron-methyl. Les mélanges des herbicides n'a pas abouti à une activité synergistique et les mélanges avec l'imazapyr et le triclopyr ont diminué l'activité de chaque composé. Il y a eu un certain renforcement de l'activité sur R. ponticum quand l'imazapyr et le métsulfuron-méthyl étaient appliqués de façon séquentielle, à 48 heures d'intervalle. Wirkung von Herbizidmischungen und Additiven auf Rhododendron ponticum An Container-Pflanzen von Rhododendron ponticum L. wurden versucht, die Wirksamkeit von Glyphosat, Imazapyr und Sulfonylharn-stoff-Herbiziden zu verstärken. Glyphosat, Imazapyr und Triclopyr allein und Metsulfuron-methyl nach Zugabe von Netzmitteln waren phytotoxisch, besonders Imazapyr und Triclopyr. Thifensulfuronmethyl und Tribenuron-methyl waren mit dem Netzmittel ‘Mixture B’ wirkungslos. Die Netzmittel ‘Mixture B’ und ‘Silwet L77’ erhöhten die Wirksamkeit von Imazapyr und Metsulfuron-methyl durchweg. Mischungen der Herbizide ließen keinen Synergismus erkennen, und die Mischung von Imazapyr mit Triclopyr verringerte die Wirksamkeit der Einzelkomponenten. Die Wirkung auf R. ponticum ließ sich erhöhen, wenn Imazapyr und Metsulfuron-methyl 48 h nacheinander angewandt wurden.     

Hygroscopic salts support the stomatal penetration of glyphosate and influence its biological efficacy

The objective of this study was to better understand the role of chaotropic and kosmotropic salts in stomatal uptake, a process that occurs in parallel with cuticular penetration and affects the bioefficacy of glyphosate. In Trial 1, salt solutions of kosmotropic (NH₄)₂SO₄ and chaotropic NaClO₃, with or without the organosilicone surfactant, Break‐Thru® S233 (BT), and with or without glyphosate, were prepared. In Trial 2, sodium salts with a kosmotropic‐to‐chaotropic nature (Na₂SO₄, NaCl, NaNO₃ or NaClO₃) and BT were prepared with or without glyphosate. At very high concentrations, the salts of a kosmotropic nature induced a slight decrease in the surface tension, whereas those of a chaotropic nature triggered a significant decrease in the surface tension. Solution droplets were deposited onto the leaves of Viola arvensis and Chenopodium album. The dried deposits were analyzed with an environmental scanning electron microscope. The salts formed structures linking the exterior to the interior of the stomata in the crystalline ([NH₄]₂SO₄) or amorphous (NaClO₃) form. However, the low surface tension alone did not appear to be the unique driving force for stomatal uptake. With glyphosate, amorphous globular structures of glyphosate salt were formed in the Na₂SO₄ (kosmotropic) solution. Differently, the salts of a rather chaotropic nature (NaNO₃ or NaClO₃) formed a colloidal matrix. In general, salt residues were observed over the periclinal cell walls and inside the stomatal chamber. Neither (NH₄)₂SO₄ nor Na₂SO₄ had a significant impact on glyphosate bioefficacy. However, the chaotropic salt, NaNO₃, enhanced the bioefficacy of glyphosate the most, with a performance that was comparable to that of the solution glyphosate + organosilicone surfactant.     

A rapid bioassay for the detection of photosynthesis inhibitors in water

A modified leaf disc buoyancy procedure for the detection of photosynthesis-inhibiting residues in water is described. The modifications proposed, mainly the presence of sodium hydrogen carbonate in the infiltration solution, increased the sensitivity of the method and reduced the time required. The substituted urea and 1,3,5-triazine herbicides diuron, linuron, monuron, atrazine, ametryn and atraton were detected below 0.7 mg litre^?1 using cucumber (Cucumis sativus L., cv. ‘Dalia’) leaf discs. A concentration as low as 0.09 mg diuron litre^?1 could be detected. Although bean (Phaseolus vulgaris L., cv. ‘Bulgarian’) leaf tissue was less sensitive in this bioassay than cucumber, 0.3 mg diuron litre^?1 could still be detected. The test, being very rapid (less than 30 min per determination) and relatively sensitive, could be used for the detection of photosynthesis inhibitors in recycled water used for irrigation.     

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.     

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.     

Study of the enhancement of herbicide activity and rainfastness by an organosilicone adjuvant utilizing radiolabelled herbicide and adjuvant

‘Sylgard® 309’ organosilicone surfactant is a very effective adjuvant for broadleaf weed control with a number of herbicides. It is also effective in providing rainfastness lo these post-emergence herbicide applications. To elucidate the basis for herbicide activity enhancement and rainfastness, the absorption of [¹⁴C]acifluorfen, [¹⁴C]bentazone and [¹⁴C]‘Sylgard 309’ were studied. Non-ionic surfactants and crop oil concentrates were used as adjuvants with [¹⁴C]acifluorfen and [¹⁴C]bentazone, respectively, for purposes of comparison. Maximum absorption of [¹⁴C]acifluorfen and [¹⁴C]bentazone was obtained within 15 min after herbicide application with the organosilicone, versus ≥ 24 h with the convenlional adjuvants. [¹⁴C]-Organosilicone absorption closely paralleled that of the [¹⁴C]-herbicides. The organosilicone appears to exert its action by increasing greatly herbicide absorption. The enhancement effect did not appear to be a function of reduced surface tension. Rainfastness appeared to be a result of greatly accelerated herbicide penetration through the leaf cuticle in the presence of the organosilicone.     

Development of a predictive uptake model to rationalise selection of polyoxyethylene surfactant adjuvants for foliage-applied agrochemicals

Composition-concentration relationships between a series of C₁₃/C₁₄ polyoxyethylene primary alcohol (AE) surfactants and the foliar uptake enhancement of five model neutral organic compounds were examined in factorially designed experiments on wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants grown under controlled environment conditions. Model compounds were applied to leaves as c.0.2-μl droplets of 0.5 g litre^?1 solutions in aqueous acetone in the absence or presence of surfactants at 0.2, 1 and 5g litre^?1. Uptake of the highly water-soluble compound, methylglucose (log octanol-water partition coefficient (P) = - 3.0) was best enhanced by surfactants with high E (ethylene oxide) contents (AE15, AE20), whereas those of the lipophilic compounds, WL110547 (log P = 3.5) and permethrin (log P = 6.5), were increased more by surfactants of lower E contents, especially AE6. However, there was little difference between AE6, AE11, AE15 and AE20 in their ability to promote uptake of the two model compounds of intermediate polarity, phenylurea (log P = 0.8) and cyanazine (log P = 2.1). Absolute amounts of compound uptake were also influenced strongly by both surfactant concentration and plant species. Greatest amounts of uptake enhancement were often observed at high surfactant concentration (5 g litre^?1) and on the waxy wheat leaves compared with the less waxy field bean leaves. The latter needed higher surfactant thresholds to produce significant improvements in uptake. Data from our experiments were used to construct a simple response surface model relating uptake enhancement to the E content of the surfactant added and to the physicochemical properties of the compound to be taken up. Qualitative predictions from this model might be useful in rationalising the design of agrochemical formulations.     

Adjuvant Effects on the Therapeutic Control of Potato Late Blight by Dimethomorph Wettable Powder Formulations

Dimethomorph is an effective Oomycete fungicide useful for the control of late blight (Phytophthora infestans, deB) on potatoes (Solanum tuberosum, L.) by preventative (prophylactic) sprays. The results of glasshouse trials using S. tuberosum plants inoculated one day prior to treatment showed that the weak to moderate curative (therapeutic) action of a wettable powder formulation of dimethomorph (WP1) could be substantially enhanced by spray tank adjuvants. A limited survey of surfactant adjuvants indicated that enhancements of performance of WP1 varied with the ethylene oxide content in two series of surfactants, C₁₂/C₁₄ alcohol ethoxylates (‘Genapol’ C series) and nonylphenol ethoxylates (‘Arkopal’ N series). Optimum enhancements were obtained with intermediate degrees of ethoxylation and ‘Genapol’ C080 was adjudged to be marginally superior to its analogues and superior to all of the ‘Arkopal’ series, as well as to a silicone ethoxylate/propoxylate (‘Silwet’ L-77), an alkylamine ethoxylate/propoxylate (‘Armoblen’ 557), and sodium sulfosuccinate (‘Aerosol’ OTB). It was also superior to an emulsifiable paraffinic/naphthenic oil (HVI 60E). Further trials established that relatively high application rates (1000–1500 g ha⁻¹) of ‘Genapol’ C080 were required for maximum enhancement and that the presence of mancozeb, as a co-fungicide, did not substantially affect the enhancement of the therapeutic performance of dimethomorph by ‘Genapol’ C080.     

Organosilicone surfactant performance in agricultural spray application: a review

The effects of organosilicone surfactants on the physico-chemical properties of spray solutions, and on foliar uptake and field performance of agrochemicals are reviewed. Aqueous solutions of organosilicone surfactants frequently have lower equilibrium surface tensions (down to 20 mN m^?1) than conventional surfactants. Dynamic surface tension of silicone surfactants, however, is not consistently lower than that of conventional surfactants. On leaf surfaces of many plant species spray droplets containing organosilicone surfactants spread completely. Organosilicone surfactants are ineffective in lowering surface tension when mixed with most conventional surfactants. However, poly-alkylene oxide surfactants do not interfere with surface tension lowering by organosilicone surfactants. Some organosilicone surfactants degrade rapidly in acidic or alkaline spray solutions and degradation adversely affects performance. Generally, organosilicone surfactants increase foliar uptake and field performance of agrochemicals more rapidly, but final uptake is not consistently different from conventional surfactants. Frequently, mass flow of the spray solution through open stomata accounts for rapid enhancement of uptake and performance. The studies reviewed suggested that some organosilicone surfactants may offer advantages over conventional surfactants, but require some precautions if their full potential is to be utilized. Revue: les tensio-actifs de type organosilicone dans la pulvérisation phytosanitaire Les effets des tensio-actifs de type organosilicone sur les propriétés physicochimiques des bouilles de pulvérisation, ainsi que sur la pénétration foliaire et l'efficacité au champ des produits phytosanitaires, sont examinés. Les solutions aqueuses de tensio-actifs organosilicones ont souvent des tensions superficielles à l'équilibre plus basses (20 nN m^?1) que celles des tensio-actifs conventionnels. Ce n'est cependant pas toujours le cas de leur tension superficielle dynamique. Sur la surface foliaire de beaucoup d'espèces végétales, les gouttelettes contenant des organosilicones s'étalent complètement. Les tensio-actifs organosilicones perdent leur faculité de baisser la tension superficielle lorsqu'ils sont mélangés à la plupart des tensio-actifs conventionnels. Cette restriction ne concerne pas les tensio-actifs de type polyalkylène oxyde. Certains tensio-actifs organosilicones se dégradent rapidement si la bouillie est acide ou alcaline, ce qui affecte leur efficacité. En général, ils accélèrent la pénétration foliaire et l'efficacité au champ des produits phytosanitaires mais la pénétration finale n'est pas différente de celle quiest obtenue avec des adjuvants conventionnels. Souvent, la pénétration de la bouillie par l'ouverture stomatique rend compte de l'augmentation de pénétration et d'efficacité. Certains surfactants organosilicones pourraient offrir des avantages par rapport aux tensio-actifs conventionnels mais qu'ils demandent certaines précautions pour que leur potentiel soit pleinement exprimé. Möglichkeiten des Einsatzes von Silikon-Tensiden in Formulierungen und Spritzlösungen Es wird ein überblick über den Einfluß von Silikon-Tensiden auf die physikochemischen Eigenschaften von Spritzbrühen, die Blattaufnahme und die Wirkung von Agrarchemikalien gegeben. Wäßrige Lösungen von Silikon-Tensiden haben oft eine niedrigere Gleichgewichtsoberflächenspannung (20 mN m^?1) als solche herkömmlicher Tenside. Die dynamische Oberflächenspannung ist mit Silikon-Tensiden jedoch nicht immer niedriger als mit herkömmlichen. Auf den Blattflächen vieler Pflanzenarten spreizen Spritztröpfchen von Lösungen mit Silikon-Tensiden vollständig. Werden Silikon-Tenside mit herkömmlichen Tensiden gemischt, so sind die Lösungen weniger oberflächenaktiv als die reiner Silikon-Tenside. Lediglich in Mischungen mit Polyalkylenoxid-Tensiden bleibt die niedrige Oberflächenspannung der Silikon-Tenside erhalten. Einige Silikon-Tenside zerfallen in saurer oder basischer Spritzbrühe schnell, wodurch ihre Wirkung beeinträchtigt wird. Der Zusatz von Silikon-Tensiden beschleunigt zwar allgemein die Blattaufnahme und Wirkung von Agrarchemikalien, doch unterscheidet sich die insgesamt aufgenommene Dosis oft nicht von der mit herkömmlichen Tensiden. Die schnellere Aufnahme und Wirkung ist in vielen Fällen auf das Eindringen der Spritzbrühe durch offene Stomata ins Blattgewebe zurückzuführen. Silikon-Tenside können gegenüber herkömmlichen Tensiden in einigen Situationen Vorteile bieten, wenn ihre spezifischen Eigenschaften beim Einsatz berücksichtigt werden.     

A scanning electron microscope study of glyphosate deposits in relation to foliar uptake

The effects of several formulations on foliar uptake of glyphosate, and on the morphology of glyphosate deposits on leaves, were examined in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.). [¹⁴C]glyphosate, in the form of the free acid or the isopropylamine salt (IPAS), was applied to foliage alone or with various adjuvants. Uptake of all glyphosate IPAS formulations was greater than that of the corresponding acid formulation. Addition of ‘Tween 20’ enhanced the uptake of glyphosate IPAS compared to glyphosate alone, but had no effect on the uptake of glyphosate acid. Ammonium sulfate and the ‘Roundup’ formulation blank increased the uptake of glyphosate acid and IPAS to 2-3 times that of herbicide alone. Surface deposits, as observed by scanning electron microscopy, varied with the formulation of the herbicide, although there were no differences between the acid and IPAS formulations. Glyphosate alone initially formed a deposit with both crystalline and smooth, amorphous areas. Later in the treatment period (48 and 72 h after application), the deposit was almost entirely crystalline. The addition of ‘Tween 20’ or of formulation blank resulted in the formation of a more amorphous, non-crystalline deposit. Herbicide solutions containing ammonium sulfate dried to form a highly crystalline deposit. However, crystals similar to those of glyphosate alone were not visible in these deposits. The ability of these adjuvants to prevent or delay crystal formation may play a role in their enhancement of herbicide uptake.     

Surfactant and salt affect glyphosate retention and absorption

The influence of nonylphenoxy surfactants and glyphosate salt formulation on spray retention, phytotoxicity and [¹⁴C]glyphosate uptake was investigated in wheat (Triticum aestivum L). and Kochia scoparia L. The amount of spray retained, and uptake of [¹⁴C]glyphosate increased with increasing hydrophilic-lipophilic balance (HLB) value of surfactants. The volume of spray delivered to the plant treatment area and retained by wheat and K. scoparia plants increased with increasing surfactant HLB values, but this only partly accounted for the higher spray retention. Spray retention by leaves of plants was not affected by calcium chloride, either alone or with ammonium sulphate in the glyphosate spray solution. [¹⁴C]Glyphosate absorption by wheat and K. scoparia was reduced by calcium chloride alone, but not in mixtures with ammonium sulphate, regardless of surfactant. Phytotoxicity and uptake of glyphosate salt formulations for wheat was: isopropylamine > ammonium > sodium > calcium; these results indicate that the surfactant selected is important to maintain glyphosate efficacy and that sodium and calcium cations antagonize glyphosate by forming salts that are absorbed less than commercial isopropylamine formulations.     

Effect of Adjuvants on the Therapeutic Activity of Dimethomorph in Controlling Vine Downy Mildew. I. Survey of Adjuvant Types

The effect of adjuvants on the performance of emulsifiable concentrate (EC) and wettable powder (WP) formulations of dimethomorph, a new systemic Oomycete fungicide, has been investigated using a two-day therapeutic (curative) assay with downy mildew (Plasmopara viticola, Berl. & de T.) on vines (Vitisvinifera L., cv. Cabernet Sauvignon) in glasshouse trials. The EC formulation had some therapeutic activity in this type of test. This activity was increased by the spray tank incorporation of 6 g litre⁻¹ of either emulsifiable rape seed oil (‘Atplus’ 412) or emulsifiable paraffinic oil (‘Atplus’ 411F). However, these improvements in performance were overshadowed by those brought about by incorporation of 3 g litre⁻¹ of a series of C₁₃/C₁₄ alcohol ethoxylates varying in ethylene oxide content from 5 to 20 moles:(‘Marlipal’ 34/6EO, 34/11EO, 34/20EO). Nearly complete fungal control was obtained in the presence of these adjuvants with a dimethomorph application rate of 25 g ha⁻¹ compared with only around 90% control at 400 g ha⁻¹ without adjuvants. The WP formulation was inactive in this therapeutic test but the presence of the adjuvants improved the performance of this formulation towards the high levels observed with the EC plus adjuvants, demonstrating that adjuvants could markedly influence the performance of solid, otherwise therapeutically inactive, dimethomorph formulations. Further trials examined other types of adjuvants (nonylphenol, alkylamine and silicone ethoxylates) but either they were no better than the alcohol ethoxylates or they induced unacceptable phytotoxicity. Trials with alcohol ethoxylates (‘Genapols’) from another source demonstrated activity equivalent to the ‘Marlipal’ surfactants. A two-factorial matrix experiment with ‘Genapol’ C050 showed that, under glasshouse conditions, >90% control could be obtained with the dimethomorph EC at 25 g AI ha⁻¹ with 375 g ha⁻¹ ‘Genapol’ C050. Applications of the WP formulation required slightly higher rates of either 50 g AI ha⁻¹ plus 375 g ha⁻¹ ‘Genapol’ C050 or 25 g AI ha⁻¹ plus 750–1500 g ha⁻¹ ‘Genapol’ C050. The overall conclusion was that alcohol ethoxylates varying in alkyl chain length from C₁₂ to C₁₈ and ethylene oxide content between 5 and 20 moles for the C₁₂ surfactants and ∽15 moles for the C₁₈ surfactants were effective adjuvants in promoting the therapeutic activity of dimethomorph formulationsagainst P. viticola on glasshouse-propagated vines.     

麦冬草对草甘膦耐药性的形态学机制

麦冬、土麦冬和阔叶土麦冬都对草甘膦具有较高的天然耐药性,其耐药性的主要机制是由于EPSPS基因结构差异、基因多拷贝以及高表达量,但是,靶标机制并不能完全解释阔叶土麦冬的耐药性最高,麦冬的耐药性最低,土麦冬居于中间。为了进一步揭示其耐药性的非靶标机制,采用光镜和扫描电镜观察了麦冬、土麦冬和阔叶土麦冬的叶表皮显微结构,发现麦冬、土麦冬和阔叶土麦冬的气孔主要分布于叶片下表皮,气孔密度分别为37.6、36.15和23.92个/mm~2。但是,土麦冬和阔叶土麦冬的气孔在叶片上表皮也有分布,并且阔叶土麦冬上表皮的气孔明显多于土麦冬。麦冬草气孔带和非气孔带细胞在细胞长度、面积和长宽比等方面均存在差异。麦冬气孔周围的表皮细胞平周壁具明显瘤状突起,导致气孔下陷;土麦冬气孔周围的表皮细胞平周壁呈波浪状突起,使气孔略下陷;阔叶土麦冬气孔周围的表皮细胞平周壁基本无突起,气孔下陷不显。这些结构特征差异可能与麦冬草对草甘膦的耐药性差异有一定的相关性。