Rationale for a natural products approach to herbicide discovery

Weeds continue to evolve resistance to all the known modes of herbicidal action, but no herbicide with a new target site has been commercialized in nearly 20 years. The so-called 'new chemistries' are simply molecules belonging to new chemical classes that have the same mechanisms of action as older herbicides (e.g. the protoporphyrinogen-oxidase-inhibiting pyrimidinedione saflufenacil or the very-long-chain fatty acid elongase targeting sulfonylisoxazoline herbicide pyroxasulfone). Therefore, the number of tools to manage weeds, and in particular those that can control herbicide-resistant weeds, is diminishing rapidly. There is an imminent need for truly innovative classes of herbicides that explore chemical spaces and interact with target sites not previously exploited by older active ingredients. This review proposes a rationale for a natural-products-centered approach to herbicide discovery that capitalizes on the structural diversity and ingenuity afforded by these biologically active compounds. The natural process of extended-throughput screening (high number of compounds tested on many potential target sites over long periods of times) that has shaped the evolution of natural products tends to generate molecules tailored to interact with specific target sites. As this review shows, there is generally little overlap between the mode of action of natural and synthetic phytotoxins, and more emphasis should be placed on applying methods that have proved beneficial to the pharmaceutical industry to solve problems in the agrochemical industry.     

Agrochemical lead optimization by scaffold hopping

Scaffold hopping, the exchange of a specific portion of a potential active ingredient with another substructure with the aim of finding isofunctional molecular structures with significantly different molecular backbones, often offers the chance in lead discovery or optimization to mitigate problems related to toxicity, intellectual property, and insufficient potency or stability. Scaffold hopping tools such as isosteric ring replacement including 1,3 nitrogen shift and cyclic imine–amide isosterism, but also ring opening and ring closure approaches, functional group isosterism, reversion of functional groups, chain shortening, chain lengthening, and scaffolds delivered by natural products, have become a permanent fixture of the innovation and optimization process in crop protection research. Their appropriate use will be explained through examples of success stories in the field of agrochemistry. Analogies to, but also differences from, the main categories of scaffold hopping in medicinal drug discovery are discussed. © 2017 Society of Chemical Industry     

Natural products that have been used commercially as crop protection agents

Many compounds derived from living organisms have found a use in crop protection. These compounds have formed the basis of chemical synthesis programmes to derive new chemical products; they have been used to identify new biochemical modes of action that can be exploited by industry-led discovery programmes; some have been used as starting materials for semi-synthetic derivatives; and many have been used or continue to be used directly as crop protection agents. This review examines only those compounds derived from living organisms that are currently used as pesticides. Plant growth regulators and semiochemicals have been excluded from the review, as have living organisms that exert their effects by the production of biologically active secondary metabolites.     

The functioning and sustainability of village crop protection brigades in Niger

In 1992 and 1993, two studies were executed in Niger to evaluate the functioning and sustainability of village plant protection brigades. The history of these brigades, their functioning, and the way the training was put into practice are discussed, as well as the problems encountered by the brigadiers. Also, the division of benefits of the brigade within the villages is dealt with. The approach adopted by the programme is discussed. It is argued that It is unlikely that many brigades will continue to exist after the end of the programme, given the costs and availability of pesticides and equipment. The fact that the bigger and richer farmers within the village benefit most undermines community based‐support. The roots of these problems can be traced back to the top‐down approach. A more participatory approach, based on the enhancement of farmers’ decision‐making and their knowledge of the environment and its risks, is advocated.     

Review: Resistance as a concomitant of modern crop protection

This paper reviews the impact of resistance to fungicides and insecticides/acaricides on the way crop protection is practised. It is now clear that resistance can develop to virtually any crop-protection product, in any pest, fungal pathogen or even weed. As a limiting factor in crop protection, it is a fact of life. A positive side-effect is the precision with which products are used today, with increasing implementation of Integrated Pest Management (IPM) programmes. This is a vital step towards sustainability. This paper describes: past experiences; current status of resistance; how resistance management influences current crop protection practices; regulatory aspects; and the outlook for the future. It concludes that EU regulations on resistance management must be simple and workable. Chemicals will continue to have a central role in optimising yields from the world's crops, as new tools, including biotechnology, become available for crop protection and resistance management. The crop-protection industry's innovations and product stewardship programmes will contribute to sustainable agriculture. This will provide continued benefits to users, the environment and society. ©1997 SCI     

Natural products in agriculture—a view from the industry

The paper discusses the use of natural products and biological control agents in crop protection from an industrial viewpoint. The criteria which must be satisfied are noted. Examples are given from the genetic engineering of baculoviruses and proteins. The final section considers the utility of natural products as a source of leads for conventional agrochemicals, and the screens needed. © 1998 SCI.     

Common vole (Microtus arvalis) ecology and management: implications for risk assessment of plant protection products

Common voles (Microtus arvalis) are common small mammals in some European landscapes. They can be a major rodent pest in European agriculture and they are also a representative generic focal small herbivorous mammal species used in risk assessment for plant protection products. In this paper, common vole population dynamics, habitat and food preferences, pest potential and use of the common vole as a model small wild mammal species in the risk assessment process are reviewed. Common voles are a component of agroecosystems in many parts of Europe, inhabiting agricultural areas (secondary habitats) when the carrying capacity of primary grassland habitats is exceeded. Colonisation of secondary habitats occurs during multiannual outbreaks, when population sizes can exceed 1000 individuals ha^?1. In such cases, in‐crop common vole population control management has been practised to avoid significant crop damage. The species' status as a crop pest, high fecundity, resilience to disturbance and intermittent colonisation of crop habitats are important characteristics that should be reflected in risk assessment. Based on the information provided in the scientific literature, it seems justified to modify elements of the current risk assessment scheme for plant protection products, including the use of realistic food intake rates, reduced assessment factors or the use of alternativee focal rodent species in particular European regions. Some of these adjustments are already being applied in some EU member states. Therefore, it seems reasonable consistently to apply such pragmatic and realistic approaches in risk assessments for plant protection products across the EU. © 2013 Society of Chemical Industry     

Potential and actual uses of zeolites in crop protection

In this review, it is demonstrated that zeolites have a potential to be used as crop protection agents. Similarly to kaolin, zeolites can be applied as particle films against pests and diseases. Their honeycomb framework, together with their carbon dioxide sorption capacity and their heat stress reduction capacity, makes them suitable as a leaf coating product. Furthermore, their water sorption capacity and their smaller particle sizes make them effective against fungal diseases and insect pests. Finally, these properties also ensure that zeolites can act as carriers of different active substances, which makes it possible to use zeolites for slow‐release applications. Based on the literature, a general overview is provided of the different basic properties of zeolites as promising products in crop protection. © 2015 Society of Chemical Industry     

Combining novel monitoring tools and precision application technologies for integrated high-tech crop protection in the future (a discussion document)

The possibility of combining novel monitoring techniques and precision spraying for crop protection in the future is discussed. A generic model for an innovative crop protection system has been used as a framework. This system will be able to monitor the entire cropping system and identify the presence of relevant pests, diseases and weeds online, and will be location specific. The system will offer prevention, monitoring, interpretation and action which will be performed in a continuous way. The monitoring is divided into several parts. Planting material, seeds and soil should be monitored for prevention purposes before the growing period to avoid, for example, the introduction of disease into the field and to ensure optimal growth conditions. Data from previous growing seasons, such as the location of weeds and previous diseases, should also be included. During the growing season, the crop will be monitored at a macroscale level until a location that needs special attention is identified. If relevant, this area will be monitored more intensively at a microscale level. A decision engine will analyse the data and offer advice on how to control the detected diseases, pests and weeds, using precision spray techniques or alternative measures. The goal is to provide tools that are able to produce high-quality products with the minimal use of conventional plant protection products. This review describes the technologies that can be used or that need further development in order to achieve this goal.     

Natural products for pest control: an analysis of their role,value and future

Natural products (NPs) have long been used as pesticides and have broadly served as a source of inspiration for a great many commercial synthetic organic fungicides, herbicides and insecticides that are in the market today. In light of the continuing need for new tools to address an ever‐changing array of fungal, weed and insect pests, NPs continue to be a source of models and templates for the development of new pest control agents. Interestingly, an examination of the literature suggests that NP models exist for many of the pest control agents that were discovered by other means, suggesting that, had circumstances been different, these NPs could have served as inspiration for the discovery of a great many more of today's pest control agents. Here, an attempt is made to answer questions regarding the existence of an NP model for existing classes of pesticides and what is needed for the discovery of new NPs and NP models for pest control agents. © 2014 Society of Chemical Industry     

植保无人飞机低空低容量喷雾技术应用与展望

近十年来,我国植保无人飞机迅猛发展,应用的农作物范围越来越广,不仅在水稻、小麦、玉米等主要粮食作物得到了应用,在橡胶、槟榔等高大植株的病虫害防治中更有其独特优势,已经初步形成了我国植保无人飞机低空低容量喷雾的喷头配置、配套药剂、飞防助剂、作业参数等技术体系,对于重要农作物病虫害如稻纵卷叶螟、水稻纹枯病、小麦蚜虫、玉米黏虫等防治效果均在80%以上,在各地病虫害防控中发挥了重要作用。但是,植保无人飞机喷雾作业过程中,还存在炸机或失控、雾滴飘移药害、药液分层结块、防治效果不稳定等问题。通过汇总分析植保无人飞机在重要病虫草害防治工作的成功经验和安全事故,本文提出植保无人飞机低容量喷雾技术将会得到更广泛的应用,植保无人飞机专用药剂和配套助剂、变量施药、多传感器数据融合、多机协同、精准施药、施药标准和规范等都将得到长足的发展,为现代农业和智慧农业发展提供技术支持。     

Methods for determining the vapour pressure of active ingredients used in crop protection. Part IV. An improved thermogravimetric determination based on evaporation rate

The vapour pressure of thermally stable substances can be determined easily at ambient pressure using the evaporation rate method. It is possible to measure the evaporation by thermogravimetry in the temperature range from 30°C to 800°C. Vapour pressures as low as 10^?10 Pa (10^?12 mbar) can be determined with excellent reproducibility.     

Fungicidal potential of methoxylated flavones from citrus for in vitro control of Colletotrichum gloeosporioides, causal agent of anthracnose disease in tropical fruits

Four polymethoxylated flavones (3,5,6,7,3',4'-hexamethoxyflavone, 3,5,6,7,8,3',4'-heptamethoxyflavone, 5,6,7,8,4'-pentamethoxyflavone and 5,6,7,8,3',4'-hexamethoxyflavone) were isolated and characterized from cold-pressed orange oil. Their antifungal activities were evaluated against Colletotrichum gloeosporioides (Penz) Penz & Sacc, a major plant pathogen of fruits that causes significant damage to crops in tropical, sub-tropical and temperate regions. Methoxylated flavones were effective in inhibiting mycelial growth of the fungus. As flavone concentration increased, mycelial growth decreased. 5,6,7,8,3',4'-Hexamethoxyflavone completely inhibited the growth of Cgloeosporioides at a concentration of 100 microg ml(-1).     

高效植保机械与精准施药技术进展

农药、植保机械（又称药械）与施药技术是影响农药喷施效果、防治效果和农药利用效率的3个同等重要的因素。药械与施药技术随着农药学科的发展而发展,整体来讲药械发展经历了人背机器、机器背人、人机分离、喷雾机器人4个典型时代。我国现有耕种面积大小不同的各类农场3.2亿个,总耕地面积1.2亿hm2,年均植保防治作业面积4亿～5亿hm2次,至今我国连续10多年的粮食连年增产,新型植保装备与高效施药技术的研发应用推广功不可没。与20世纪相比,在新千年前20年,国内外药械和施药技术与高速发展的绿色农药生产相互适应、相互促进,进入了快速发展的轨道,至2020年我国植保机械社会保有量突破2.5亿台,自走式喷杆喷雾机260多万台,各类果园喷雾机150多万台,植保无人机10多万台;新型植保装备与高效施药技术为农药减量提供了手段,助推了农药利用率的提高和农药的减量计划的实施。2020年全国水稻、玉米、小麦三大粮食作物的农药利用率达到40.6%,较2015年提高了4个百分点,新型植保装备与高效施药技术为解决诸如农药有效利用率低、操作人员中毒、农药残留超标和环境污染等问题做出了突出贡献。特别是在我国自走式喷杆喷雾机、...     

Implementing a globally harmonized risk assessment‐based approach for regulatory decision‐making of crop protection products

A global, harmonized evaluation system for crop protection chemicals based on exposure and risk will improve the ability to inform risk management decisions and better support innovation. This would be achieved through harmonized risk assessment‐based regulatory decision‐making realized through the application of the best available science, via integration of new methods and traditional data to create tailored exposure‐driven risk assessments. A requirement to achieve success is a structure that encourages direct communication between the regulatory community and the regulated industry, which would enable a more rapid incorporation of new technologies and advancing science. An approach that emulates the International Conference of Harmonization (ICH) for pharmaceuticals would bring together regulatory authorities and the regulated industry along with relevant experts from academia and Non‐Governmental Organizations to discuss scientific and technical advances and their implementation. These discussions would also encourage the elimination of outmoded practices that no longer serve a purpose resulting in more uniform testing requirements and best practices for data evaluation to support safe use and scientifically defensible human health and environmental risk assessments. New and developing technologies offer exciting opportunities to improve the current toxicity testing paradigms to provide better solutions and diminish animal testing. Implementation of a harmonized approach will increase the speed, efficiency and accuracy of regulatory decision‐making for human health and environmental protection while increasing the efficiency of providing safe and effective innovative products to the agriculture community. © 2020 Society of Chemical Industry     

Methods for determining the vapour pressure of active ingredients used in crop protection. Part V: Thermogravimetry combined with solid phase microextraction (SPME)

The well-established evaporation rate method for determining the vapour pressure of active ingredients in crop protection down to the order of 10^-12 mbar can be supplemented by the new sample preparation technique of Solid Phase MicroExtraction (SPME). With this technique, it is possible to identify evaporating substances by analysis after partitioning into the polymer coating of a thin fibre in the outlet-gas flow of thermogravimetric equipment. The active ingredients fenpropimorph, kresoxim-methyl, metolachlor, clomazone and (Z)-9-dodecenyl acetate were used in this study, which showed that, despite the relatively small amount of collected material, an analytical identification of the evaporating compound by SPME/GC can be successfully achieved. In particular, the experiments have demonstrated a clear correlation between the linearity of the weight loss curve and the evaporation process of a pure compound. In the case of organic compounds that are unstable to heat, the SPME method can also be utilized to show whether, and at what temperatures, decomposition of the sample into fragments of higher volatility occurs. For example, the insecticide dimethoate showed a clear temperature dependence of both evaporation behaviour and in the SPME/GC analysis. © 1998 SCI     

Screening study for potential lead compounds for natural product-based fungicides: I. Synthesis and in vitro evaluation of coumarins against Botrytis cinerea

An efficient, one-pot synthesis of angular and linear dihydropyranocoumarins, along with C-6 and C-8 prenylated coumarins is reported. These compounds, together with single- and furanocoumarins, were tested for their potential antifungal activity against the phytopathogen Botrytis cinerea Pers ex Fr. The results show that furanocoumarins may be able to control the fungus B cinerea.