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.     

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。     

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.     

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.     

Studies on the site of uptake by plants of chlortoluron and terbutryne

Experiments were done to observe the pattern of early root development of radish (Raphanus raphatnistrum L.) and perennial ryegrass (Lolium perenne L.), the mobility of chlortoluron following application to the soil surface, the effect of protecting the subterranean shoots of four plant species on their response to chlortoluron and terbutryne and the relative quantities of ¹⁴C-labelled chlortoluron taken up by radish and Avenu fatua from root and shoot zone exposure. Both chlortoluron and terbutryne appear to be able to enter the plants examined, Alopecurus myosuroides, Stellaria media, perennial ryegrass and radish, through roots and shoots. It is suggested that shoot uptake is relatively more important for plants like perennial ryegrass than for those whose roots develop more quickly and invade the soil above the seed, such as radish. The quantities of radioactive chlortoluron taken up from soil containing 400 ng g^?1 showed that less than 3 ng per plant could reduce A. fatua fresh weight by 17–40% while over 30 ng per plans had little effect on radish. By comparison 2 kg ha^?1 chlortoluron applied to the soil surface of pots which were sub-irrigated for 3 weeks gave a concentration of 170 ng g^?1 in the layer of soil 10–12 mm from the surface. It is suggested that for shallow germinating species with herbicides of physical and phytotoxic properties similar to chlortoluron, the solvent action of rainfall, together with diffusion, is enough to allow the transport of toxic quantities to the target plant although any leaching action is likely to increase activity.     

The effects of six adjuvants on the rainfastness of chlorpyrifos formulated as an emulsifiable concentrate

The chemically different adjuvants ‘Agral’, ‘Bond’, ‘Codacide Oil’, Li 700, ‘Silwet L’-77, and ‘Headland Guard’ were assayed to determine their effects on the rainfastness of an emulsifiable concentrate formulation of the organophosphorus pesticide chlorpyrifos. Cabbage leaves were each treated with 200×0.25-μl droplets of diluted formulation using a hand-held microapplicator. Droplet deposits were left to air-dry for 1 h prior to exposure to simulated rainfall. Rain fastness was assessed using GC residue analyses of treated leaves after exposure to 10, 20 or 30 min simulated rainfall. The results indicated that the latex-based adjuvants ‘Bond’ and ‘Headland Guard’ induced a statistically significant increase in rainfastness, results for the other adjuvants assayed being either not significant or inconclusive. The results are discussed within the context of using adjuvants to enhance insecticide efficacy. ©1999 Society of Chemical Industry     

Imazaquin Spray Retention,Foliar Washoff and Runoff Losses under Simulated Rainfall

Spray retention and foliar washoff of imazaquin in smooth pigweed (Amaranthus hybridus L.) and sicklepod (Senna obtusifolia (L.) Irwin and Barneby) were investigated. Imazaquin (70 g AI ha⁻¹) was applied alone, with nonionic surfactant ‘X-77’ or organosilicone-based nonionic surfactant ‘Kinetic’ to plants at two- to five-leaf stage and subjected to 2·5 cm rainfall in 20 min either 1 or 24 h after application. Imazaquin spray retention was higher with adjuvants than without. Retention was similar between adjuvants in smooth pigweed but ‘Kinetic’ retained twice as much imazaquin as ‘X-77’ in sicklepod. Rainfall 1 h after application washed off three-quarters of foliar residues regardless of plant species or adjuvant. However, at 24 h after application, foliar washoff was lowest with ‘Kinetic’ followed by ‘X-77’ in both species. Imazaquin washoff ranged from 33 to 88% in the two species at 24 h after application. Overall, imazaquin activity was similar with either adjuvant in smooth pigweed but ‘Kinetic’ was more effective than ‘X-77’ in sicklepod. Runoff losses from the surface of a Bosket sandy loam (Mollic Hapludalfs) soil in runoff trays (1·2% slope) were also studied. Imazaquin was applied as above to trays with and without smooth pigweed canopy. A 2·5-cm rainfall was applied in 20 min at 24 h after application. Runoff samples collected in one-litre fractions were analyzed by enzyme-linked immunosorbent assay. Sediment (but not water) in runoff was greatly reduced (56%) by pigweed cover as compared to bare trays. Imazaquin in the first litre of runoff was higher than in subsequent runoff fractions regardless of pigweed cover. Total imazaquin lost in runoff was higher in pigweed cover (23%) than bare trays (16% of applied). Imazaquin concentration in 10–20 cm soil depth in pigweed cover trays was higher than in bare trays. These results suggest that imazaquin is vulnerable to foliar washoff and the herbicide washed off could move in the aqueous phase due to shorter contact time with soil for sorption.     

Influence of light, temperature and humidity on the translocation and activity of glyphosate in Elymus repens (=Agropyron repens)

The effects of light, température and humidity on the performance and translocation of glyphosate in Elymus repens (L.) Gould (=Agropyron repens L. (Beauv.)), during the period of 48 h after treatment, were studied in controlled-environment cabinets. Increases in the levels of all three factors resulted in increases in herbicide performance. In general, these differences were statistically significant at all treatment periods except the longest when almost full control was achieved. The results highlight the important influence of environmental factors on herbicide performance during the short-term, post-spraying period. The application of ¹⁴C-labelled glyphosate to the adaxial leaf-sheath surface resulted in very rapid uptake and was used as a method of treating plants to study herbicide translocation under different environmental conditions. Increased light levels and temperatures enhanced basipetal translocation to the crowns and rhizomes but increased humidity had no significant effect with this form of application.     

The selectivity of methabenzthiazuron between barley, perennial ryegrass and Poa trivialis

In field experiments methabenzthiazuron at 1.1 kg ai/ha applied pre-emergence gave good control of Poa trivialis L. in perennial ryegrass S23 which was undersown in spring barley (Zephyr); no significant damage to barley or perennial ryegrass resulted from 2.2 kg ai/ha. However this dose applied when barley had three to four leaves decreased the subsequent barley yield. In pot experiments in the glasshouse methabenzthiazuron was active mainly due to uptake through the soil. Much greater damage to barley and perennial ryegrass resulted when herbicide-treated soil was placed below seed level than above the seed. The difference was less marked with P. trivialis. The latter started to develop secondary roots near the soil surface earlier than either perennial ryegrass or spring barley.     

The effect of the herbicide glyphosate on non‐target spiders: Part I. Direct effects on Lepthyphantes tenuis under laboratory conditions

We examined the toxic effects of glyphosate to adult female Lepthyphantes tenuis (Araneae, Linyphiidae), a common spider of agricultural habitats. The overspray technique was used to investigate the effect of the herbicide on forty individuals in each of six glyphosate treatments (2160, 1440, 1080, 720, 360 and 180 g ha^?1) and a distilled water control. Spiders collected from the wild were individually placed in exposure chambers and checked every 24 h over a 72‐h experimental period. Mortality of L tenuis remained at less than 10% in all treatments at 24 and 48 h after spray application, and only increased marginally (to 13%) after 72 h. These results support other limited data which suggest that glyphosate is ‘harmless’ to non‐target arthropods. More extended laboratory testing to investigate any side‐effects of glyphosate on the life history of L tenuis and other non‐beneficial invertebrates is required. © 2001 Society of Chemical Industry     

Glyphosate‐resistant Italian ryegrass (Lolium multiflorum) on rice paddy levees in Japan

The rapid range expansion of naturalized Italian ryegrass (Lolium multiflorum Lam.) in farmland is a serious problem in Fukuroi city in Shizuoka Prefecture, Japan. Glyphosate has been used to control Italian ryegrass in the levees of rice paddy fields and wheat fields for ～20 years, but this weed in Fukuroi city is poorly controlled by glyphosate. In order to elucidate the level of resistance to glyphosate in Italian ryegrass populations, seed bioassays and a foliar application experiment, using seeds collected from 16 wild populations in and around Fukuroi city and from three susceptible cultivars, were conducted. For the susceptible cultivars and one population from a site where glyphosate had not been applied for >10 years, the shoot length in the seed bioassays was greatly suppressed at a glyphosate concentration of 10 mg ai L^?1 and no seedling survived after the foliar application of glyphosate at a rate of 2.3 kg ai ha^?1. Nine wild populations from levees in the southern part of Fukuroi city showed vigorous shoot growth at a glyphosate concentration of 10 mg ai L^?1 and had at least a 78% survival rate after the application of glyphosate at 2.3 kg ai ha^?1. Four wild populations from levees in the northern part of Fukuroi city showed a slight suppression of the shoot growth as a result of the glyphosate treatment and their survival rates ranged from 20 to 64%. The results suggested that resistance to glyphosate has evolved in the wild populations of Italian ryegrass that are growing on the levees. This is the first report of a glyphosate‐resistant weed in Japan.     

杂草种类、叶龄及药后降水时间对烟嘧磺隆药效的影响

温室盆栽条件下研究了反枝苋Amaranthus retroflexus、马唐Digitaria sanguinalis、稗草Echinochloa crus-galli、牛筋草Eleusine indica和苘麻Abutilon theophrasti 5种杂草对烟嘧磺隆的敏感性。结果表明:反枝苋和稗草对该药剂最敏感,而苘麻对烟嘧磺隆的耐药性最高。药液中添加2.5 mL/L的有机硅助剂Silwet L-77提高了对除马唐以外的所有草种的防除效果,表明在作用于马唐时Silwet L-77与烟嘧磺隆之间存在拮抗作用。杂草叶龄对烟嘧磺隆的药效有明显的影响,3~5叶期施药,防效高达89.9%以上,而7叶期的防效只有75%。药后1.5 h和3.0 h降水3 mm降低了烟嘧磺隆的防效,但药后6.0 h降雨对药效无显著影响。烟嘧磺隆与Silwet L-77混用,可提高药剂对反枝苋的抗雨水冲刷能力,但对马唐的效果没有提高。     

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.     

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.     

Seed germination behavior of glyphosate‐resistant and susceptible Italian ryegrass (Lolium multiflorum Lam.)

Ryegrass (Lolium multiflorum Lam.) is one of the most difficult annual weeds to control in cultivation systems worldwide, especially in temperate regions. The widespread use of herbicides in the past two decades has selected resistant biotypes of ryegrass in crops in Southern Brazil. Ryegrass seeds are dormant when disseminated and germination can be staggered over time (crop‐growing season). Knowledge of the germination behavior of seeds from herbicide‐resistant plants has been little studied, but it would be very useful in integrated weed management. Thus, this study aimed to characterize the dynamics of the soil seed bank of two biotypes of L. multiflorum, one glyphosate‐resistant and the other glyphosate‐susceptible, under a no‐tillage system. The treatments were arranged in a bifactorial scheme, using seeds from biotypes (glyphosate‐resistant and glyphosate‐susceptible) with monthly periods of removal from field (one to 12 months). Seeds of each biotype were placed on the soil surface and covered with soil and straw to simulate no‐till conditions. The percentage of germinated, dormant, and dead seeds was evaluated every 30 days. The ryegrass seed bank of glyphosate‐susceptible and glyphosate‐resistant biotypes was reduced to 11 and 15% of dormant seeds, respectively, at the end of 12 months. However, there was no variation in germination, dormancy, and seed mortality between susceptible and glyphosate‐resistant ryegrass. Seeds of glyphosate‐resistant biotype and susceptible showed germination behavior with similar dynamics in the soil over a period of 12 months.     

A target-site mutation is present in a glyphosate-resistant Lolium rigidum population

Annual ryegrass (Lolium rigidum) is the only weed species to have evolved resistance to the broad‐spectrum herbicide glyphosate in Australia. A population that had failed to be controlled by glyphosate was collected from a vineyard in the Adelaide Hills region of South Australia. Dose–response experiments on this population (SLR 77) showed that it was glyphosate resistant, with an LD₅₀ that was 1.9–3.4 times higher than that of a susceptible population (VLR 1). The movement of radiolabelled glyphosate within SLR 77 plants showed that this population did not have the differential glyphosate translocation mechanism of resistance common to several other Australian glyphosate‐resistant populations. Subsequent analysis of shikimic acid accumulation within the plant after glyphosate treatment showed that this population accumulated significantly less shikimic acid than a susceptible population, but more than a glyphosate‐resistant population with the translocation mechanism, indicating the possible involvement of another mechanism of resistance. Sequencing of a portion of the SLR 77 5‐enolpyruvylshikimate‐3‐phosphate synthase gene was carried out and a mutation causing an amino acid change at position 106 from proline to threonine was identified. This mutation is likely to be responsible for glyphosate resistance in this population, as mutations in this position have been found to be responsible for glyphosate resistance in goosegrass (Eleusine indica) from Malaysia. This paper represents the first report of target‐site glyphosate resistance in L. rigidum and provides evidence that this species has at least two mechanisms of glyphosate resistance present in Australia.     

Low detection of glyphosate in rivers following application in forestry

BACKGROUND

Glyphosate is the most commonly used herbicide in the world, and is used in agriculture, forestry, and urban settings. In regions with high glyphosate use, such as agricultural, glyphosate and its' major derivative aminomethylphosphonic acid (AMPA) are frequently detected in surface waters. In Canadian forestry glyphosate-based herbicides are used to control vegetation that competes with conifer trees and are applied one to two times during a rotation, leading to infrequent application to the same area. Forestry occurs over a large spatial extent, and the cumulative application in space can lead to a large percentage of the land base receiving an application through time. To assess the frequency and concentration of glyphosate and AMPA in surface waters of a region where forestry is the dominant use sector, we conducted three monitoring programs targeting: (i) immediately after application, (ii) after rainfall, and (iii) cumulative application over a large spatial extent.

RESULTS

Across all monitoring programs we collected 296 water samples between August and October from eight river systems over two years and detected glyphosate in one sample at 17 ppb.

CONCLUSION

Glyphosate is not likely present in surface waters during baseflow conditions as a result of applications in forestry. Lack of detection is likely because soil capacity to bind glyphosate remains high due to infrequent applications to the same area, and factors that limit sediment transport to surface waters such as buffers. Additional sampling is needed during other stream conditions, ideally spring freshet, to determine peak concentrations. © 2023 National Research Council Canada. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. Reproduced with the permission of the Minister of Innovation, Science, and Economic Development.     

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.     

Effect of Adjuvants on the Therapeutic Activity of Dimethomorph in Controlling Vine Downy Mildew. II. Adjuvant Mixtures,Outdoor-Hardened Vines and One-Pack Formulations

Previous investigations have shown that certain C₁₂–C₁₈ alcohol ethoxylates with between 5 and 20 moles ethylene oxide gave large enhancements to the therapeutic activity of emulsifiable concentrate (EC) and wettable power (WP) formulations of dimethomorph in controlling two-day-old infections of downy mildew (Plasmopara viticola, Berl. & deT) on glasshouse propagated vines (Vitis vinifera, L.). In a continuation of that work it has been shown that similar enhancements could also be obtained on vines that had been grown under outdoor conditions for two to three weeks before treatment (outdoor-hardened vines) and it is concluded that the treatments would therefore be effective on field vines. Mixtures of either ammonium sulfate or the silicone ethoxylate, ‘Silwet’ L77, with the best alcohol ethoxylates, ‘Genapol’ C050 or ‘Genapol’ C080, produced slight antagonism of the action of the ‘Genapols’ and therefore were of no benefit. Trials with one-pack formulations prepared containing the ‘Genapol’ adjuvants produced good dose response curves from which estimated doses for 90% fungal control (ED₉₀ values) could be calculated by Logit analysis. These one-pack formulations were significantly more effective than the standard EC formulation (ED₉₀=335 g AI ha⁻¹, glasshouse vines and 445 g AI ha⁻¹, outdoor hardened vines) with optimum enhancements with those formulations containing an adjuvant: dimethomorph ratio of either 9:1 on glasshouse vines (ED₉₀= 13 g AI ha⁻¹) or 6:1 on outdoor-hardened vines (ED₉₀=30 g AI ha⁻¹). This last result was significantly better than that obtained with a commercial formulation of cymoxanil, ‘Fytospore’, (ED₉₀=86 g AI ha⁻¹) and encouraged the recommendation that these one-pack formulations should be examined in field trials.     

The fungicide tridemorph as a selective herbicide for the control of Holcus lanatus in ryegrass and of Bonus sterilis in barly

The potential of the fungicide tridemorph selectively to control established plants of Holcus lanatus L. in ryegrass (Lolium perenne L) and Bromus sterilis L. in barley (Hordeum vulgare L.) was examined in glasshouse trails. A dose of 4.2 kg ha^?1 tridemorph gave selectively between H. lanatus and ryegrass similar to, but more costly than, that which would be provided by 1.2 kg ha^?1 asulam. B sterilis was more sensitive to tridemorph than was barley. Two additives, glycerol and the oil-surfactant mixture ‘PF’ enhanced this selectivity when tridemorph was applied at 2.1 kg ha^?1.