A compartmental computer model of foliar uptake of pesticides

The uptake and movement of a chemical into a wheat leaf has been simulated in a 5-compartment model. The compound is considered to be applied to the leaf as discrete droplets of solution, from which water evaporates at a uniform rate. Solute diffuses from the droplets through the plant cuticle into the epidermal cell wall, and from there either into and out of the cytoplasm and vacuole of the mesophyll cells or along cell walls to the xylem. Once in the xylem it is carried in the transpiration stream towards the tip of the leaf. Accurate values for the parameters required by the model have not yet been measured, but the model simulates in a qualitative manner the movement pattern observed for 1-methyl-2-pyridone. The results presented focus attention on the possible importance of membrane permeability in determining the phytotoxicity of xylem mobile pesticides.     

Photolysis of pesticides: influence of epicuticular waxes from Persica laevis DC on the photodegradation in the solid phase of aminocarb,methiocarb and fenthion

Pesticides with N,N‐dimethyl and thiomethyl moieties (aminocarb, methiocarb and fenthion) were irradiated under artificial light (λ > 290 nm) in an amorphous wax phase from Persica laevis DC. The effect of the presence of the wax on the photolysis rate differed in the three pesticides, increasing it in aminocarb, having little effect in methiocarb and slowing it down in fenthion. The presence of the wax affected the qualitative photodegradation behaviour of all the pesticides. The data obtained were compared with those for pirimicarb, which had been studied earlier. © 2001 Society of Chemical Industry     

Influence of metolachlor and the metolachlor protectant CGA 43089 on the biosynthesis of epicuticular waxes on the primary leaves of Sorghum bicolor Moench

Epicuticular wax synthesis by the primary leaf of Sorghum bicolor seedlings is inhibited when the germinating seeds are treated with 5 ppm metolachlor before germination. The composition of the free and esterified primary alcohols plus free and esterified fatty acids and aldehydes have been analysed. The predominant alcohol (75%) had 32 carbons while the 28- and 30-carbon homologues accounted for 78% of the fatty acids. Treatment of the germinating seeds with metolachlor strongly inhibited formation of the C₂₈, C₃₀ and C₃₂ alcohols. Synthesis of C₃₀ and C₃₂ fatty acids was decreased while that of the C₂₆ homologues was somewhat elevated. Simultaneous treatment of the germinating seed with metolachlor and the herbicide protectant CGA 43089 (α-[cyanomethoximino]-benzacetonitrile) resulted in normal wax synthesis. The results lead to the conclusion that the protectant prevents metolachlor from inhibiting synthesis of the dominating C₂₈ to C₃₀ chain-length constituents of the sorghum epicuticular wax.     

Control of foliar diseases in barley: towards an integrated approach

Barley is one of the world??s most important crops providing food and related products for millions of people. Diseases continue to pose a serious threat to barley production, despite the use of fungicides and resistant varieties, highlighting the impact of fungicide resistance and the breakdown of host plant resistance on the efficacy of control measures. This paper reviews progress towards an integrated approach for disease management in barley in which new methods may be combined with existing measures to improve the efficacy of control in the long-term. Advances have been made in genetic mapping of resistance (R) genes and in identifying novel sources of genes in wild barley populations and land races. Marker assisted selection techniques are being used to pyramid R genes to increase the durability of resistance. Elicitors to induce host resistance used in combination with fungicides can provide effective disease control in the field and could delay the evolution of fungicide insensitivity. Traits that may contribute to disease tolerance and escape have been identified and the extent of genetic variation within barley germplasm is being determined. Tools are being developed to integrate the above methods via an assessment of the risk of economic injury occurring from disease to guide decisions on the requirement for fungicide treatment. Barriers exist to the adoption of integrated management approaches from growers and end-users further down the supply chain (e.g. acceptance of variety mixtures) and policy incentives from government may be required for it to be taken up in practice.     

农药在植物中的内吸和传导行为与施药技术研究进展

农药的施用方式和施用效果与其在植物中的内吸和传导行为密切相关.农药在植物表面和内部的内吸和传导行为,不仅与其自身理化性质有关,还受植物种类、生长期、生长条件及施药方式等因素的影响.研究农药在植物体内的内吸和传导行为及其影响因素,对于选择合适的施药技术及提高农药利用率具有重要的指导意义.本文综述了农药在植物体内的内吸和传...     

The foliar uptake of isoproturon by wheat and Alopecurus myosuroides huds

The uptake and translocation of ¹⁴C-isoproturon (3-p-cumenyl-1-1,-dimethylurea) in wheat (tolerant) and backgrass (sensitive) following foliar treatment under controlled environmental conditions were examined. The amount of ¹⁴C-isoproturon translocated through the xylem was about 10 times that translocated through the phloem in both wheat and blackgrass. However, 25.5% of the applied ¹⁴C-isoproturon was translocated in the xylem in blackgrass, compared with 8.9% in wheat. ¹⁴C-isoproturon did not respond significantly to induced sink-demand in either species. Leaf-disc autoradiograms revealed the absorption of ¹⁴C-isoproturon by the minor veins and translocation into the cut vein endings. No significant differences were found in between wheat and blackgrass in this respect.     

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.     

Benzimidazole pesticides: Analysis and transformations

Some properties, analysis and transformations by plants, animals, soil and light of benomyl, carbendazim, thiabendazole, fuberidazole, cypendazole and fenazaflor are discussed.     

Spray retention, foliar uptake and translocation of glufosinate and glyphosate in Ambrosia artemisiifolia

Ambrosia artemisiifolia plants exhibit stomata on both leaf surfaces and three types of trichomes: (i) small (<50 μm) spherical or ovoid, (ii) medium‐sized (50–100 μm) and (iii) long (100–200 μm) and sharp. Only the long and sharp trichomes were stained with AgNO₃, indicating the presence of hydrophilic domains. Epicuticular waxes appeared amorphous, consistent with high levels of spray retention. Glufosinate was readily taken up by A. artemisiifolia leaves, with maximum uptake of >80% of the applied label, and half maximum uptake being reached within 6 h. The foliar uptake of glyphosate was nearly complete and half of it was attained after 3 h. Glufosinate and glyphosate were ambimobile and their translocation out of the treated leaves amounted to 13–16% and 11–15% of the absorbed radioactive label respectively. Glufosinate was mainly directed to the apical developing tissues, with less amounts reaching the tissues below the treated leaves. Glyphosate was directed towards the sink tissues (apical developing tissues and roots). The sensitivity of A. artemisiifolia to glufosinate and glyphosate can be explained by high spray retention, rapid and important foliar uptake, and appreciable migration out of the parts of the plant hit by the spray.     

Influence of wetting agents on the foliar uptake and herbicidal activity of glufosinate

The influence of four different wetting agents on the foliar retention, uptake and herbicidal activity of the glutamine synthetase inhibitor, glufosinate, was examined in growth-chamber experiments on barley (Hordeum vulgare L. cv Roland) and barnyard grass (Echinochloa crus-galli (L.) P.B.) as test species. The non-formulated monoammomum salt, glufosinate-ammonium, was applied as a spray, either alone or mixed with a wetting agent. The dose rates of herbicide and wetting agent were 0.5 g a.i. litre^?1 and 2.0 g litre^?1, respectively, on barnyard grass, and 2.0 g a.i. litre^?1 and 60 g litre^?1, respectively, on barley. Herbicide damage, rated 10 days after spraying, was greatest when glufosinate was used with a sodium C₁₂/C₁₄-alcohol-diglycolether sulfate (FAEO-sulfate) and least with polyoxyethylene (POE)(8) tridecyl ether; intermediate effectiveness was obtained with a combination of herbicide and a POE(15) tridecyl ether or POE(15)-tallow amine. The activity of the target enzyme, glutamine synthetase, measured 2 h after spraying, was reduced most when FAEO-sulfate was present and least with POE(8) tridecyl ether. The behaviour of the glufosinate wetting agent solutions on plant foliage was analysed by measurements of spray retention, droplet contact angles and foliar uptake of [¹⁴C]glufosinate. The results led, for both grass species, to the conclusion that differential ability of the wetting agents to enhance the permeation of glufosinate from the leaf surface deposit into the leaf tissue was the main factor responsible for the differences in herbicidal effectiveness of the glufosinate/wetting agent combinations used in this study.     

农药兑水茎叶喷施对靶沉积剂量传递与调控研究进展

农药兑水茎叶喷施对靶沉积是一个复杂的剂量传递与分布过程，涉及制剂形成、药液配制、雾化分散、空间运行、叶面沉积和稳态持留等动态过程，受到药剂特性、环境因素、为害规律、植株形态和叶面结构等多因素影响，在水稻、小麦和玉米三大粮食作物上对靶沉积率为40.6%。其中，对不同区域、不同靶标作物种植体系中农药损失规律和高效利用机理研究与认识不足，是农药对靶沉积剂量传递效率低的主要原因之一。本文以农药向靶标作物及有害生物传递的过程行为为主线，将农药兑水茎叶喷施对靶沉积的剂量传递过程分解为雾滴空间运行、叶面动态沉积和稳态持留3个过程，从空间维度综述了各过程中的表观现象与行为、损失规律及其调控机制途径与技术等；从技术发展与进步角度，分析了农药对靶沉积剂量传递与调控研究和认知的发展思路，概述了典型代表性成果，提出了未来研究与发展建议。期望客观认知农药高效对靶沉积的损失规律与调控机制，探析主控过程与影响因子，提出农药减量施用调控方法、控制技术指标及功能助剂施用限量标准等，为农药减施增效关键技术与产品研发提供理论与技术支持。     

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-enhanced foliar uptake of some organic compounds: Interactions with two model polyoxyethylene aliphatic alcohols

Interactions occurring during the surfactant-enhanced foliar uptake of seven model organic compounds were examined using two homogeneous surfactants, hexaethylene glycol monotridecyl ether (C13E6) and hexadecaethylene glycol monododecyl ether (C12E16). Surfactant–compound and compound–surfactant interactions were detected by measurement of their relative uptake rates following application of c. 0·2 μl droplets of the corresponding radiolabelled formulations. The magnitude of surfactant–compound interaction was found to vary according to the physicochemical properties of both the compound and the surfactant, and was influenced by surfactant concentration and target plant species. Interactive and non-interactive mechanisms, both leading to substantial enhancement of compound uptake, could be identified, but their precise nature could not be elucidated. Although penetration of C13E6 into the site of application appeared to be essential in order to activate the uptake of a compound, substantial absorption of C12E16 was not always required to produce the same effect. The results are discussed in the light of possible sites and modes of action for activator polyoxyethylene surfactant adjuvants.     

PEG渗透胁迫下3份大麦材料幼苗叶片抗旱生理特性分析

以甘啤4号、哈瑞特和D- 22大麦为材料,测定不同浓度PEG6000(5％、10％、15％、20％、25％和30％)渗透胁迫处理下大麦幼苗叶片的相对含水量、Pro含量等生理指标,分析PEG渗透胁迫模拟干旱对大麦生理生化特性的影响.结果表明,随着PEG溶液浓度的增加,三个材料的大麦幼苗叶片的相对含水量均下降,而脯氨酸含量...     

作物从土壤中吸收、传递和累积农药的研究进展

农药是保障粮食安全的重要农业投入品,施用后部分农药会沉积在土壤中,甚至会被作物根部吸收,进入作物体内并累积于可食部位,从而导致潜在农产品质量安全问题。研究表明,土壤中的有机质含量、农药的辛醇-水分配系数和作物脂质含量是影响作物吸收非离子型农药的关键因素,作物各部位的脂质含量是影响该类农药累积的关键因素,借助蒸腾作用向上传递是作物根部吸收传导农药的主要动力。本文重点综述了农药被作物的根部吸收、传递和累积及其主要影响因素,结合植物吸收模型的发展及运用,展望了该领域未来发展方向,为农药归趋及应用风险研究提供参考。     

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

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

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.     

Considering degradation kinetics of pesticides in plant uptake models: proof of concept for potato

BACKGROUND

Degradation kinetics of pesticides in plants are crucial for modeling mechanism-based pesticide residual concentrations. However, due to complex open-field conditions that involve multiple pesticide plant uptake and elimination processes, it is difficult to directly measure degradation kinetics of pesticides in plants. To address this limitation, we proposed a modeling approach for estimating degradation rate constants of pesticides in plants, using potato as a model crop. An operational tool was developed to backward-estimate degradation rate constants, and three pesticides were selected to perform example simulations.

RESULTS

The simulation results of thiamethoxam indicated that the growth dynamics of the potato had a significant impact on the degradation kinetic estimates when the pesticide was applied during the early growth stage, as the size of the potato determined the uptake and elimination kinetics via diffusion. Using mepiquat, we demonstrated that geographical variations in weather conditions and soil properties led to significant differences in the dissipation kinetics in both potato plants and soil, which propagated the variability of the degradation rate constant. Simulation results of chlorpyrifos differed between two reported field studies, which is due to the effect of the vertical distribution of the residue concentration in the soil, which is not considered in the majority of recent studies.

CONCLUSIONS

Our proposed approach is adaptable to plant growth dynamics, preharvest intervals, and multiple pesticide application events. In future research, it is expected that the proposed method will enable region-specific inputs to improve the estimation of the degradation kinetics of pesticides in plants. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.