Author: Zhang Yi Xuan Shanghai Pesticide Research Institute
Thiocarbamates are a class of pesticides, some of which are fungicides and some of which are herbicides. The dithiocarbamate thiocarbamate fungicide was developed in the 1940s and is a major breakthrough, becoming the most popular and widely used organic chemical fungicide for the control of various crop fungal diseases. . Dithiocarbamates include dialkyldithiocarbamates (eg, thiram, thiram, rammed iron) and alkylene bisdithiocarbamate (eg, mancozeb, sensen zinc) , mancozeb, desensen, methyl dexame zinc). The latter, also known as ethylene bisdithiocarbamate (EBDC), is the first broad-spectrum leaf fungicide. EBDC is an old and reliable product that has been used to control plant diseases for more than 50 years after introduction and continues to be used. These fungicides act on multiple sites and are often used in combination with many single-site biocides to manage resistance. This paper describes the potential role of dithiocarbamate in the management of modern biocide resistance development at specific sites, in particular the widely used sub-class EBDC fungicides of dithiocarbamate and its future development. prospect.
1 development and characteristics
1.1 Development
The development of antifungal dithiocarbamate compounds in the 1940s is believed to have opened up an active period of new fungicide synthesis. The first patent for dithiocarbamate fungicides was granted in 1934 by thiram (ethylene dithiocarbamate (EBDC), which was commercialized primarily as a seed coating in 1940. Soon Later, thiram iron (dimethylammonium sulphate) and its closely related thiram (zinc dimethyldithiocarbamate) were developed in 1942. The first EBDC compound developed was dysen sodium (Asian Sodium ethyl bisdithiocarbamate), commercialized in 1943, and then commercialized in 1945. Dyson zinc is sodium sulphate and zinc sulphate (zinc ethylene bisdithiocarbamate) The reaction products are widely used to control potato early and late blight, and later used in other vegetable and fruit crops. Under continuous research and development, another EBDC fungicide (ethylene bis-dithio) in 1950 Manganese carbamate is patented and is more effective than zinc. In 1962, a complex of zinc ions and manganese, namely mancozeb (ethylene bis-dithiocarbamate and 2% zinc) Ion) is registered as the most important and widely used dithiocarbamate fungicide. In 1958 and 1 respectively In 963, two EBDC compounds were developed, namely, polys[ammine[ethylenebis(dithiocarbamato)]zinc(2+)][tetrahydro-1,2,4,7-dithiadiazocine-3,8-dithione And methyl dexame zinc (zinc bis(dithiocarbamate), a foliar and fruit protectant.
1.2 Mechanism and characteristics
Dithiocarbamate fungicides release EBIS (ethylene-bis-isothiocyanatesulfide) in water, which interferes with different biochemical processes in fungal cytoplasm and mitochondria. EBIS is a thiol inhibitor that inactivates the sulfhydryl groups of the amino acids of the enzyme and forms complexes with metal-containing enzymes. Therefore, it can disrupt different metabolic processes such as lipid metabolism, fungal respiration, and adenosine triphosphate (ATP) production.
Dithiocarbamate has many important properties that can be developed as an important tool for the chemical management of plant diseases. Compared with inorganic copper and sulfur preparation products, it has high safety to crops and can be rapidly degraded by hydrolysis, oxidation and photolysis in the environment. Dithiocarbamates are compatible with the most commonly used fungicides, insecticides and acaricides, but the compatibility of the two must be verified before mixing with the cream formulation. Such products are incompatible with Bordeaux blends, fixed copper compounds (compoundcoppercompounds) or stone sulphur compounds.
Dithiocarbamate has only a preventive effect. This fungicide remains on the surface of plants, does not penetrate the epidermis, has no systemic, and has no therapeutic effect. Due to degradation, photolysis and rain erosion, dithiocarbamate can not be left on the leaf surface for a long time, so it must be reused. Once a week, it can protect the old and new parts of plants well. The host plant is protected by inhibiting the germination of the fungal spores and preventing the spore buds from entering the host tissue. However, laboratory studies have shown that the EBDC fungicide mancozeb has less effect on the expansion of mycelium and disease of Phytophthorainfestans in invasive leaf tissue, but prevents sporangia formation and swimming in actual disease control. The germination of the spores.
1.3 toxicity
The use of dithiocarbamate fungicides also has side effects. In laboratory studies, EBDCs such as mancozeb, mancozeb, and dexame zinc interfere with animal reproduction and endocrine. The effects of mancozeb, mancozeb and mancozeb on thyroid function and waterlogging are related to its metabolite ethylenethiourea (ETU). ETU has the potential to cause birth defects and cancer in laboratory animals and has been classified as a human carcinogen by the US Environmental Protection Agency. Because EBDC can be converted to ETU (except for methyl dexamethasone), some countries have considered limiting the use of these fungicides, but so far there is no direct evidence that the use of dithiocarbamate bactericides has led to human cancer. . Mancozeb has moderate to low acute toxicity to rats, mice, hamsters, cats and sheep, while Daisenlian is not toxic to rats by acute oral, transdermal and inhalation. The World Health Organization believes that it is unlikely that there will be an acute risk of Daisenlian and Mancozeb when operated on a label.
1.4 Disease prevention
Global foliar application of dithiocarbamate fungicides to control about 400 fungal pathogens in more than 100 crops. They are mainly used in potato, grape, citrus, apple, pomegranate, tomato, melon and banana trees, and are also important for controlling cereals, corn, peanuts, Brassica, onions, beets, asparagus, nuts, lawns and flower diseases. Dialkyldithiocarbamate thiram is mainly used for seed treatment, while thiram and thiram are mainly used for foliar treatment of fruits, vegetables and flowers. Dithiocarbamates are effective against all major classes of fungal pathogens, such as ascomycetes, basidiomycetes, and deuteromycetes and oomycetes. The use of these fungicides can significantly increase crop yields. In general, EBDCs are more effective than dialkyl subclasses of carbamates.
2 The sensitivity of the pathogen to the dithiocarbamate is unchanged
Dithiocarbamate fungicides have been routinely used worldwide for more than 50 years and there have been no records of resistance cases so far. The Biocide Resistance Action Committee classifies the mechanism of action of dithiocarbamate as M (multiple site effect), indicating a low/negligible risk of resistance development. Dithiocarbamate acts on multiple sites in the target fungal cell, so several mutations in the target gene or one detoxification metabolic pathway is required to promote the emergence of resistance. Interestingly, these low-resistance risk characteristics also apply to thiocarbamate (category N) herbicides . In the laboratory, the fungi were chemically mutagenized by increasing the concentration of the bactericide or exposing the bactericide to ultraviolet light, and studying the resistance of some fungi to daisenlian, mancozeb and senseng zinc. In some cases, resistance developed, but not stable, and the resistant lines returned to their original sensitivity after continued cultivation with the fungicide-free medium, so the target pathogens in the enhanced field trials It is not possible to develop resistance to dithiocarbamate soon. Several reports have shown that EBDC has been routinely used to control different fungal and oomycete pathogens of different crops for several years, and the sensitivity of fungicides has not decreased.
3 management of resistance to other fungicides
Fungicide resistance is a challenge to manage many important fungal diseases, threatening the commercial potential of some powerful single-site biocides. Major fungal pathogens for single classes of major classes such as benzimidazole, diimide, benzamide, demethylation inhibitors, phenylaminopyrimidine, QoIs fungicides, carboxylic acid amides and succinate dehydrogenase inhibitors Point inhibitors have developed resistance. In some cases, significant crop losses are caused by the failure of disease control. Before introducing single-site compounds, growers generally use dithiocarbamates and other protective fungicides to prevent the development of the disease without encountering resistance problems. Although single-site inhibitors generally have better control effects and have partial therapeutic advantages, dithiocarbamates are still widely used to control several diseases. These multi-site biocides are an important part of the resistance management strategy, which can delay the development of single-site biocide resistance in the mixture.
3.1 for blends or wheels
Fungicides are often used in combination to broaden the spectrum of control and to delay the selection of resistant individuals in the pathogen population. Dithiocarbamate fungicides and single-site biocides are used to delay the development of multiple pathogen resistances that cause significant losses to crops. Among the mixed dithiocarbamates, mancozeb is the most popular and specific site sterilization of benzamide, benzimidazole, demethylation inhibitor and methoxy acrylate. A fungicide for mixing agents. Other EBDCs, such as mancozeb, methyldyne, zinc, and dexamethasone, are also commonly used in combination with many single-site biocides. Starting from the introduction of these fungicides, it is a rule that benzamide and other antibacterial fungicides are mixed with EBDC fungicides before packaging to delay the development of resistant strains. This has become an effective and practical strategy for the development of resistance to high-risk pathogens such as Phytophthora, Trichoderma, Pythium, Potentella, Pythium and similar fungal pathogens. EBDC fungicides containing zinc and/or manganese, such as mancozeb, mancozeb, dexamethasone and methyl dexamethasone, are mainly used in France to work with single-site bactericides to manage grape downy mildew resistance. Strategy. Dithiocarbamate is effective against both resistant and susceptible pathogens. Mixing can not only reduce the rate of evolution of pathogenic bacteria to risky mixed components, but also reduce the recommended dosage without reducing control. This strategy helps to extend the effective use of many single-site biocides.
Dithiocarbamates are also used with single-acting site bactericides to delay the evolution of pathogen population resistance. Both mixed and rotational use are considered effective strategies to delay the development of risky biocide resistance, although there are differences in their perceptions of efficacy. Most trials have shown that mixed resistance development is slower than round. Even if substantial levels of resistance have emerged, mixing often has good results and can reduce crop losses.
The dithiocarbamate has a lower control effect under high disease pressure, but the obtained control effect is considered to be satisfactory because the dithiocarbamate reduces the development of single-site biocide resistance. risk. Many single site biocides and dithiocarbamate premixes have been commercialized.
3.2 synergy with compatible fungicides
Although it is sometimes difficult to distinguish the additive and synergistic effects of the components of the mixture, there are examples of the synergistic effect of the mixture containing the EBDC bactericide such as mancozeb and methyl dexamethasone. In the case where one of the ingredients in the mixture has developed resistance, the advantage of synergism is particularly pronounced, and the dosage can be reduced.
In several disease control studies, it was found that there is synergistic effect between benzamide and mancozeb. In the control of grape and cucumber downy mildew, the potato and tomato late blight in the mixture is more effective than the corresponding concentration of each single agent. However, the degree of synergy depends on the concentration of the dithiocarbamate compound in the mixture. The combination of azoxystrobin and methyldyne zinc with a 1:6 mixture has a higher control effect against Phytophthora capsica than other ratios, indicating that the synergistic effect of this ratio is stronger.
4 future prospects
The discovery and development of new action mechanisms of fungicides helps to manage the resistance of existing fungicides, but because most new compounds act on single-sites, there is a certain level of resistance to the disease. Dithiocarbamates and other multi-site broad-spectrum fungicides, such as phthalimide (sterilized mono) and chlorinated nitrile (chlorocyanil) are fungal disease-protecting plants and management single-acting sites An important means of point biocide resistance. EBDC is still of great use worldwide, especially in developing countries due to its low cost and better use alone or in combination with single-site biocides to better control disease. However, the potential risks of ETU formation by degradation of dithiocarbamate may limit its use. The challenge of effectively controlling disease and managing resistance with dithiocarbamate is to minimize the impact on users, consumers and the environment.
4.1 Comprehensive use
The purpose of the resistance management strategy is not only to slow down the evolution of target pathogen resistance, but also to prevent disease and reduce crop yield losses. Integrated Disease Management (IDM) can delay or even avoid the development of risky fungicide resistance. Bactericides, resistant crop varieties, cultivation methods, and biological control agents are all part of IDM, and the fungicides may be used less frequently in each growing season, so the selection pressure is low. The use of fungicides in IDM strategies is also beneficial in situations where resistance has occurred.
Dithiocarbamates, risky fungicides and resistant genotype plants are used together for IDM to better control disease and manage the resistance of fungicides. This has been tested and achieved good results. Planting potato varieties with multi-gene resistance to late blight, and then applying reduced amount of mancozeb, can better control the disease and reduce the risk of resistance to the resistance of Phytophthora infestans to metalaxyl. Similarly, the cultivation of sunflowers with multiple resistance genotypes, the application of mancozeb, metalaxyl and azoxystrobin or mancozeb and azoxystrobin mixtures compared with only the application of metalaxyl and mancozeb Can better prevent the development of Plasmoparahalstedi resistance to metalaxyl. In the IDM strategy, the amount of dithiocarbamate and site-specific bactericides is reduced, so their residual risk in the environment is reduced.
4.2 Slow release of active ingredients
Dithiocarbamate nanoformulations are currently being developed which are capable of controlling the release of active ingredients, further enhancing their biological activity and transitibility, reducing the amount required, and killing germinated spores with greater efficiency. With polyethylene glycol as the "blocking agent", nano-formulation of mancozeb has been developed, which has good control effect on target pathogenic bacteria and has less impact on the environment than traditional preparations. The micro-encapsulation of the compound into hyperbranched polycitric acid has led to the development of a zinc-based nano-formulation. Similar nano-formulations of other EBDCs are currently being developed, and if commercialization is successful, this will reduce the use rate and the harmful effects on the environment and humans.
5 summary
Dithiocarbamate has been used worldwide for decades to control many economically important plant diseases. Such fungicides have a broad spectrum of activity, a large number of sites, and a low risk of development of target pathogen resistance. Dithiocarbamate has been successfully used as a compatibilizing ingredient to delay the selection and emergence of single-site biocide resistance. This lays the foundation for the blending strategy and is the cornerstone of the anti-resistance strategy. If they remain cost effective, they may continue to be used to prevent crop yield losses.
However, the widespread use of EBDC fungicides has raised concerns about their occupational and ecotoxicological hazards. The main management challenge is that some of the major metabolites of dithiocarbamate, ETU, are thought to interfere with mammalian endocrine. In 2005, due to this problem, people called for the ban on mancozeb, but the US Department of Agriculture believes that the actual risk is very low if it is used according to the recommended amount of the label, and this bactericide is an important part of the anti-resistance strategy, so it refuses This request was made. The World Trade Organization has retained mancozeb, sensitized zinc, mancozeb, methyldyne zinc and other dithiocarbamates with a toxicity class of U, indicating that these fungicides are unlikely to cause in conventional applications. Acute hazard. The successful development of its nanoformulations will help reduce the dose used and minimize the toxic effects on animals and humans.
Most of the new compounds have high activity against fungal pathogens of different crops, but have a single action site mechanism for specific target sites of fungal cells, and therefore, it is easier to develop resistance. Dithiocarbamates will likely continue to play an important role in anti-resistance strategies, extending the useful life of biocides with high activity and novel mechanisms of action. The combined use of dithiocarbamates, risky fungicides and moderately resistant plant varieties will further contribute to the continued management of disease and reduce the risk of resistance and ecotoxicity.
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(Source: World Agrochemical Network)
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