Foliar uptake of pesticides—Present status and future challenge

Uptake of pesticides into plant foliage varies with plants and chemicals, and can be greatly influenced by adjuvants and environmental conditions. It is known that the penetration of pesticides into plant leaves is related to the physicochemical properties of the active ingredients, especially molecular size and lipophilicity. However, the uptake rate of a compound cannot be predicted by either of them or even combination of them. For a specific chemical, uptake varies greatly with plant species and there is no simple method at the moment to quickly evaluate the leaf surface permeability of a plant. Various adjuvants are being used to increase the penetration of pesticides into target plant foliage, but their effects vary with chemicals and plant species. The mechanisms of action of adjuvants in enhancing pesticide uptake remain unclear despite the effort made during the last three decades. Modern analytical and microscopic techniques provide powerful tools to deepen our understanding in this field. However, a more multidisciplinary approach is urgently needed to elucidate the transcuticular diffusion behaviour of pesticides and the mode of action of adjuvants. A better understanding of the foliar uptake process should lead to a more rational use of pesticides and minimize their negative impact on the environment.     

助剂在除草剂应用中的作用及发展前景

对助剂在除草剂中的应用历史、国外现状、发展趋势进行了综述。主要内容有助剂在除草剂中的作用,如抗飘移、兼容、沉积、去泡、水质调节等及相应的助剂品种;按来源和化学结构,助剂的类型有表面活性剂类、油类、无机盐类等,这些助剂对除草剂活性提高都有促进作用。文中指出了生物源、环境相容性、低水生生物毒性、易降解、对作物没有毒害的高效新型助剂是助剂开发的方向,并介绍了部分国外新品种;作者还对我国应采取的对策提出了建议。     

Effects of relative humidity and substrate on the spatial association between glyphosate and ethoxylated seed oil adjuvants in the dried deposits of sessile droplets

BACKGROUND: In recent years, several studies have shown the impact of adjuvants on the characteristics of herbicide deposits on leaf surfaces. Until now, most studies have addressed the distribution of active ingredients (AIs), whereas few experiments have focused on the location of the adjuvants. The objective of this study was a systematic examination of the particle distribution profile of both the AI (glyphosate, Gly) and the adjuvants after the application of sessile microdroplets on hydrophobic (Teflon) and hydrophilic (glass and aluminium) model surfaces. RESULTS: The association degree (AD) was surface dependent and specific for the tested adjuvants. In general, the rather hydrophobic adjuvant RSO 5 showed decreasing AD with Gly at increasing relative humidity (RH) levels. The rather hydrophilic RSO 60 adjuvant displayed higher AD between the compounds at a higher RH. A high concentration of the adjuvant reduced the AD for both of the RSO adjuvants evaluated. CONCLUSION: The combination of surface properties, the type of adjuvant and the relative humidity determines the degree of association between Gly and the adjuvants. The present results suggest that the interaction between the AI and an adjuvant determines whether spatial separation occurs, whereas physical processes (e.g. capillary particle movement, inward and outward Marangoni flows and the evaporation rate) are decisive for the extent of the separation. Coffee‐ring structures were formed exclusively with the adjuvant + Gly mixtures, whereas Gly alone formed either one big deposit or several small islands distributed within the droplet footprint. Copyright © 2011 Society of Chemical Industry     

喷雾助剂对茎叶处理除草剂的增效机制及应用研究进展

农田草害的发生严重影响了农业生产和发展,使用除草剂进行化学防治是目前最省时省力和防除效果最好的除草方法.其中,茎叶处理除草剂因其具有不受土壤环境影响、按草施药、灵活和选择性高等优点,应用范围更广.然而,茎叶处理除草剂在喷雾施药过程中由于受到杂草叶片界面特性的影响,常出现药液迸溅、滚落、难以渗透等现象,导致除草剂用量增大...     

Modelling penetration of plant cuticles by crop protection agents and effects of adjuvants on their rates of penetration

A theory of cuticular penetration of crop protection agents (CPAs) is presented, which incorporates properties of cuticles and cuticular waxes as well as properties of active ingredients and adjuvants. Based on this theory, two models are developed which are analytical in the sense that they help to quantify and understand (i) differences in permeability among cuticles from different species, (ii) effects of properties of CPAs on permeabilities of cuticles and rates of uptake and (iii) the effects of adjuvants on properties of cuticles and rates of uptake of CPAs. The models can be used to predict rates of uptake of CPAs as affected by properties of cuticular waxes, active ingredients and adjuvants. However, before this can be done, a constant, two parameters and at least two variables must be estimated. Properties of cuticles are accounted for by the constant D⁰/Δx and the parameter β′. The former, the ratio of the mobility of a hypothetical molecule having zero molar volume (D⁰x) divided by the path length (Δx) across the cuticle, has the dimension of velocity (ms^?1) and is independent of the solubility of the CPA. The latter is a measure of size selectivity of the cuticle. Differences in permeabilities of cuticles from different species increase with increasing size of active ingredients due to size selectivity (β′). Removing cuticular waxes from Citrus cuticles increased D⁰/Δx by a factor of 2042, while β was not affected. Differential solubility of CPAs is considered part of the driving force and at least two different partition coefficients are needed to account for differences in solubilities in cuticular waxes, cutin, water and the formulation residue on the surface of the cuticles. Adjuvants are solvents in the formulation residue on the leaf surface once the carriers (water and other volatile solvents) have evaporated and certain adjuvants also act as accelerators; they penetrate the cuticle and increase D⁰/Δx. Thus, accelerators increase rates of uptake and this effect depends on two factors, (i) the intrinsic activity of the accelerator and (ii) rate of penetration into the cuticle, because the active ingredients follow the accelerator front across the cuticle. Since accelerators penetrate from the formulation residue into the cuticle, the volume of the formulation residue decreases with time. This maintains high concentrations of CPAs in the formulation residue and, thus, maximum driving forces and rates of penetration. To utilise fully this dual accelerator effect, it is necessary to match velocities of penetration of accelerators and active ingredients accurately.     

Assessing the risk of pesticide environmental impact in several Argentinian cropping systems with a fuzzy expert indicator

BACKGROUND: The introduction of transgenic soybean (Glycine max, L.) varieties resistant to glyphosate (GR soybeans) has rapidly expanded in Argentina, increasing pesticide use where only grasslands were previously cultivated. The authors compared an estimate of environmental risk for different crops and active ingredients using the IPEST index, which is based on a fuzzy‐logic expert system. For IPEST calculations, four modules are defined, one reflecting the rate of application, the other three reflecting the risk for groundwater, surface water and air. The input variables are pesticide properties, site‐specific conditions and characteristics of the pesticide application. The expert system calculates the value of modules according to the degree of membership of the input variables to the fuzzy subsets F (favourable) and U (unfavourable), and they can be aggregated following sets of decision rules. IPEST integrated values of ≥ 7 reflect low environmental risk, and values of < 7 reflect high risk. RESULTS: Alfalfa, soybean and wheat showed IPEST values over 7 (low risk), while maize had the lowest IPEST values (high risk). Comparing active ingredients applied in annual and perennial crops, atrazine and acetochlor gave the highest risks of environmental contamination, and they are mainly used in maize. Groundwater was the most affected compartment. CONCLUSIONS: Fuzzy logic provided an easy tool combining different environmental components with pesticide properties to give a simple and accessible risk assessment. These findings provide information about active ingredients that should be replaced in order to protect water and air from pesticide contamination. Copyright © 2010 Society of Chemical Industry     

Use of the scanning electron microscope and cathodoluminescence in studying the application of pesticides to plants

The efficacy of a pesticidal formulation is in part affected by the surface to which it is applied. During the drying process, spray drops can interact with the complex microenvironment of trichomes, secretory glands, stomata, epicuticular wax and cuticle of the leaf epidermis. The subsequent uptake and persistence of the deposit can be further influenced by the action of the microclimate, including humidity, temperature, rain and dew. The scanning electron microscope (SEM), which is an instrument ideally suited for the study of the surface of bulk specimens, has been used to show the spreading and distribution of pesticides applied as sprays and individual drops to leaf surfaces. Particle size, crystal growth and co-precipitation of the active ingredient with surfactants and other adjuvants have also been investigated. The SEM can also show how some pesticides and their adjuvants continue to be taken up by the leaf long after the drops have visibly dried. Phytotoxicity, sometimes associated with the penetration of active ingredient or formulation adjuvant, can also be demonstrated using the microscope, especially if either specifically emits cathodoluminescence. These images can also supply complementary information concerning the persistence of deposits, provided that interpretation of the results is carried out with care and, if possible, in conjunction with residue and biological assays.     

Bacterial biodegradation of ethoxylated surfactants

Agricultural, industrial and domestic use of surfactants leads to the entry of these compounds into terrestrial and aquatic ecosystems. Synthetic surfactants vary significantly in structure, but most consist of alkyl or alkylphenol groups attached to nonionic or anionic hydrophilic moieties. Continued use of these compounds is usually justified on the basis that they do not cause pollution problems because they undergo biodegradation by micro-organisms present in soils and surface waters. In accomplishing biodegradation, micro-organisms, predominantly bacteria, are exploiting these potentially useful resources of reduced carbon to derive energy and support growth in situations which are otherwise frequently oligotrophic. This paper reviews aspects of surfactant biodegradation, especially in relation to alcohol and alkylphenol ethoxylates used extensively as adjuvants for agrochemicals. In principle, bacteria can employ two strategies to gain access to the aliphatic chains in alcohol ethoxylate surfactants: separation of the hydrophobic chain from the hydrophile (central fission), or direct attack on the -terminal of the alkyl chain of the intact surfactant. Direct exo-cleavage of ethylene glycol units from the polyethylene glycol (PEG) chain also provides a third route to assimilable carbon. In pure cultures of known degraders or in mined environmental samples, all three strategies are exploited, some even within the same organism. Central fission occurs predominantly at the alkyl-ether bond, but may also occur within the PEG chain itself, thus producing various glycol intermediates which accumulate in pure cultures but appear only transiently in mixed environmental samples. Against this background, the relative resistance of some alkylphenol ethoxylates to biodegradation can be assessed in mechanistic terms. The steric bulk of the aryl nucleus effectively eliminates the central fission pathway. Moreover, some alkyl phenol ethoxylates contain branched alkyl chains which restrict ω-β-oxidation. As a result, ethoxylate shortening appears to be the major course of biodegradation observed so far. Not surprisingly, these surfactants are observed to undergo extensive primary biodegradation (removal of surfactant properties) but relatively restricted ultimate degradation to carbon dioxide and normal cell components.     

Evaluating ecological‐niche factor analysis as a modelling tool for environmental weed management in island systems

Management actions are essential for mitigating the potentially harmful changes in biodiversity, ecosystem function and crop/forest productivity caused by invasive species. Species distribution models, if reliable, could be used to design effective management strategies. Although several modelling methods well suited for studying invasive species have been developed for presence‐only data, often the size of available data sets for modelling is small and results are not validated with test samples. Moreover, the impact of such methods in practical applications has been overlooked. Here, we evaluated the reliability of the modelling approach based on ecological‐niche factor analysis (ENFA) implemented in Biomapper software when applied to environmental weed data in the Azores. Presence‐only data sets of two top invasive woody species (Pittosporum undulatum and Acacia melanoxylon) were used. The continuous Boyce curve was used for validation, calculated either in Biomapper (cross‐validation) or based on test samples. The species' most habitable areas that should be regarded as management targets were thus estimated from modelling and validation. By imposing size restrictions on the presence‐only data sets used in modelling and validation, other habitable areas were defined and compared. The ENFA proved to be a suitable method for modelling environmental weed distributions, regardless of the presence‐only dataset size. Moreover, the cross‐validation of Biomapper was reliable, although its results should be interpreted with caution as they could potentially lead to statistically different management target areas.     

Altered pesticide use on transgenic crops and the associated general impact from an environmental perspective

The large-scale commercial cultivation of transgenic crops has undergone a steady increase since their introduction 10 years ago. Most of these crops bear introduced traits that are of agronomic importance, such as herbicide or insect resistance. These traits are likely to impact upon the use of pesticides on these crops, as well as the pesticide market as a whole. Organizations like USDA-ERS and NCFAP monitor the changes in crop pest management associated with the adoption of transgenic crops. As part of an IUPAC project on this topic, recent data are reviewed regarding the alterations in pesticide use that have been observed in practice. Most results indicate a decrease in the amounts of active ingredients applied to transgenic crops compared with conventional crops. In addition, a generic environmental indicator -- the environmental impact quotient (EIQ) -- has been applied by these authors and others to estimate the environmental consequences of the altered pesticide use on transgenic crops. The results show that the predicted environmental impact decreases in transgenic crops. With the advent of new types of agronomic trait and crops that have been genetically modified, it is useful to take also their potential environmental impacts into account.     

British and European community regulations and registration requirements for non-pesticidal co-formulants in pesticides and for adjuvants

Pesticides in Great Britain are subject to legislation that requires them to be approved by Ministers. Specific data for non-pesticidal co-formulants are not generally required but are encompassed within the requirements for the formulated pesticide in which they are present. Adjuvants, substances without significant pesticidal properties which enhance the effectiveness of a pesticide when added to that pesticide, can be used with pesticides only in accordance with the approval of that pesticide or as varied by lists of authorised adjuvants published by Ministers. Data must be supplied for adjuvants to appear on this list. National legislation on pesticides is soon to be amended to take account of a European Community Directive which seeks to harmonise registration requirements throughout the Community. It is as yet unclear how this will affect registration of co-formulants and adjuvants.     

飞防助剂和施药液量对植保无人飞机喷施雾滴沉积和棉花蓟马防效的影响

为明确飞防助剂和施药液量对植保无人飞机喷施在棉花冠层的雾滴沉积和对棉花上蓟马防效的影响,选择倍达通、功倍、杰效丰和迈丝4种飞防助剂,设置3种施药液量,通过田间试验研究了植保无人飞机喷施25%噻虫嗪水分散粒剂后其在棉花冠层的雾滴密度、覆盖率、沉积量和雾滴均匀性以及对棉花上蓟马的防效。结果表明,4种飞防助剂和3种施药液量对植保无人飞机喷施的雾滴沉积和蓟马防效均有显著影响。增加施药液量可显著增加雾滴在棉花冠层的密度与覆盖率,添加飞防助剂对雾滴密度的提升效果显著。4种助剂对农药雾滴在棉花冠层上、中、下部的覆盖率的影响趋势较为一致,与棉花冠层上部相比,对中、下部位覆盖率的影响较低。施药液量为2 L/667 m²时,添加倍达通、功倍、杰效丰、迈丝及无助剂对照的雾滴穿透性分别为46.0%、49.1%、33.6%、36.1%和44.3%,该施药液量下各处理雾滴穿透性均较好。随着施药液量增加,药后1、3、7 d对棉花蓟马的防效也显著提升。在相同施药液量下,25%噻虫嗪水分散粒剂药液中添加飞防助剂倍达通和杰效丰相较于功倍和迈丝,对棉花蓟马具有更高的防治效果。试验结果为植保无人飞机防治...     

Factors Influencing Aerial Insecticide Application to Forests

A successful aerial insecticide application is one that provides the desired degree of pest control at an economic cost, with little environmental impact. This paper discusses a broad range of factors that affect treatment efficacy and environmental impact from aerial insecticide application to forests. Efficacy is affected by parameters such as the choice of active ingredient and its application rate, the volume application rate, tank mix characteristics, the spray droplet size spectrum, and the timing of, and meteorological conditions during an application. Environmental impact is influenced by aspects such as active ingredient specificity, meteorological conditions during the application, avionics use and buffer zone width. Key differences between insecticide applications in forestry and agriculture are pointed out.     

Effects of alcohols,glycols and monodisperse ethoxylated alcohols on mobility of 2,4-D in isolated plant cuticles

Effects of n-alcohols, ethoxylated alcohols and glycols on mobility of 2,4-dichlorophenoxy acetic acid (2,4-D) in cuticular membranes (CM) isolated from bitter orange (Citrus aurantium L.) leaves were studied. 1-Heptanol, 1-octanol and 1-nonanol had the highest effects, as they increased solute (2,4-D) mobility by 25- to 30-fold. Increasing the number of carbon atoms in the alcohols decreased their effectiveness. Ethoxylation of alcohols did not increase 2,4-D mobility and effectiveness decreased with increasing ethoxylation. Free glycols had no effect on solute mobility in isolated cuticles. The results show that ethoxylation is not required for increasing solute mobility in cuticles. It is suggested that alcohols and ethoxylated alcohols are sorbed in cuticular waxes and plasticize them. The data show that alcohols and ethoxylated alcohols having between seven and ten carbon atoms are powerful accelerator adjuvants, as long as the degree of ethoxylation is not too high. Free short-chain alcohols synthesized by leaves may act as endogenous plasticizers and modulate permeabilities of cuticles, depending on environmental and growing conditions.     

甲酯化油助剂对氯虫苯甲酰胺在甘蓝叶片上沉积的影响

室内模拟研究了5种自制甲酯化油类助剂与氯虫苯甲酰胺喷雾液桶混对其物理性状及在甘蓝叶片上沉积的影响。结果表明,供试5种助剂均可不同程度降低药液的表面张力及缩短药液干燥时间,并增加氯虫苯甲酰胺在甘蓝叶片上的最大持留量及抗雨水冲刷力,增强农药的渗透性。花生油酸甲酯助剂(MPOA)对药液喷雾性能改良作用最为明显。添加0.02%的MPOA可降低药液表面张力28%左右,甘蓝叶片最大持留量增加约4倍,而且可大大增强药剂的渗透性。     

Adjuvants and herbicidal efficacy – present status and future prospects

The influence of adjuvants on spray liquid behaviour and herbicide performance is reviewed. Total formulation efficacy can be expressed as a function of [deposition:retention:uptake: translocation:a.i. toxicity]. Adjuvants influence the physico-chemical and plant interactions involved for each factor. Deposition efficiency of spray droplets on to a target is dependent largely on the droplet spectrum, whereas retention performance is dependent on plant leaf surface character, orientation and canopy architecture, as well as droplet volume, velocity and dynamic surface tension effects. Uptake into plant foliage is affected by the leaf surface wax, cuticle age and composition and species variability. Uptake can be improved through appropriate formulation to provide either stomatal infiltration or much greater and faster cuticular absorption of the active ingredient. The inherent translocation capability of the a.i. is not affected directly by adjuvants, which are relatively immobile, but they can increase the mass of absorbed a.i. translocated, as a consequence of improved uptake or may reduce it as a result of localized contact phytotoxicity. Considerable progress has been made in developing models of spray droplet deposition, adhesion and retention, as well as uptake. In future, individual models may be combined to provide an integrated formulation efficacy decision support system.     

Optimizing diquat efficacy with the use of adjuvants

Optimizing diquat efficacy with the use of adjuvants may broaden the spectrum of weed control, but relevant research towards this direction is limited. Field and greenhouse experiments were conducted to evaluate the effect of diquat applied alone and with six commercial adjuvants (surfactants and oil-based adjuvants) on various weed species. Diquat effect was evaluated in two field experiments on natural populations of common lambsquarters (Chenopodium album L.), prostrate knotweed (Polygonum aviculare L.) and burning nettle (Urtica urens L.) along with two greenhouse trials on rigid ryegrass (Lolium rigidum L.). In field or greenhouse experiments, all the adjuvants significantly increased the control of C. album, P. aviculare, and L. rigidum, from 48, 42 and 7%, up to 82, 74 and 67%, respectively, in terms of fresh weight reduction, but to a different extent for each adjuvant. U. urens was totally (100%) controlled in terms of visual estimation either with diquat or with diquat plus any adjuvant. The differences in the effect of diquat applied with adjuvants mainly depended on the weed species examined and they were not proportional to the surface tension reduction of the spray solution caused by the adjuvants. Overall, the surfactants and the oil-based adjuvants examined in this study considerably enhanced the effect of diquat; this can broaden the spectrum of weed control against broadleaf and grass weeds in orchards and non-crop areas. The results are discussed in relation with the classification of the adjuvants.     

Weed control on hard surfaces in The Netherlands

The non-agricultural use of pesticides in The Netherlands declined in the period 1986-2001 from 127000 to 40000 kg AI per annum. However use on pavements rose from 23% to 50% of the total non-agricultural use. To diminish the dependency on herbicides, both preventive and curative non-chemical weed control methods have been examined. In the future both mechanical and thermal methods can be improved. On a flat pavement mechanical methods are preferred because they are more effective. Two approaches are used by municipalities to lower the environmental impact of the use of herbicides on pavements. The first is to phase out the use of chemicals on hard surfaces and the second is the integrated approach in which herbicides are not prohibited, but used only on places and at times when the risk of run-off is below a mutually accepted level. Both approaches can be effective.     

喷雾助剂对苯唑草酮防除玉米田杂草的减量增效作用

为了评价不同喷雾助剂对苯唑草酮减量施用下的增效作用,采用仪器分析和田间试验的方法研究了7种助剂对30%苯唑草酮悬浮剂的药液特性和杂草防效的影响。结果表明,7种助剂均能显著降低药液的表面张力、接触角和干燥时间,增加药液铺展直径。其中,杰效利对表面张力和接触角的影响最大,迈丝和渗透者对干燥时间的影响最小。田间试验结果表明,添加迈丝和渗透者对苯唑草酮的增效作用好于其他助剂,苯唑草酮的田间用量可以减少30%以上。