In 1971, Monsanto developed the epoch-making broad-spectrum herbicide Glyphosate in the world's agriculture. Glyphosate isopropylamine salt, amine salt and sodium salt were introduced in the mid and late 1970s; ICI launched the top three in 1989.é” salt. At present, glyphosate has become the most widely used and most productive pesticide variety in the world, and its annual sales have always ranked first in pesticides. In recent years, with the development of genetically modified glyphosate resistant crops, the use of glyphosate has increased year by year, which not only affects the development direction of new varieties, but also has a major impact on the market pattern of existing herbicide varieties. Railway Fence,Road Fence,Barrier Snow Fencing Yongzhong Wiremesh Co., Ltd. , http://www.hbwires.com
1 Properties and dosage forms of glyphosate 1.1 Chemical structure Glyphosate is a very stable compound in the form of acids and their salts:
1.2 Physicochemical properties Glyphosate is white, odorless solid; density 1.74g / ml, melting point 200 ° C (no decomposition), 45 ° C vapor pressure 2.45 × 18-8 KPa (1.84 × 10-7mmHg); at 25 ° C, pH Storage at 5.7 ~ 9 hours is stable for 32d. The solubility in water at 25 ° C is 15.7 g / l (pH 7) ~ 11.6 g / l (pH 2.5), and the isopropylamine salt is 900 g / l (pH 7) ~ 786 g / l (pH 4).
1.3 The dosage form is processed into a salt or an ester based on glyphosate acid. Due to the poor absorption of acid by plants, glyphosate acid is easy to precipitate at high doses, especially at low liquid discharge. Therefore, the activity of acid is usually lower than that. Salt. The most commonly used dosage form is "Roundup" containing isopropylamine salt, which is significantly soluble in water; typically a soluble liquid (SL) containing 365 g/l or 480 g/l of active ingredient. In recent years, Monsanto has introduced a high content of glyphosate (94%), soluble granules and tablets. Surfactants and synergists are very important in the processing of glyphosate formulations. Ammonium sulfate and diammonium sulfate are commonly used activators. Glyphosate isopropylamine salt is a weak acid that can be dissociated in solution. The anionic part of the molecule is the active ingredient. They can be combined with other cations such as Ca2+, Mg2+, K+, Na+, Fe2+/3+ in the spray solution. In combination, salts formed by plants are not easily absorbed, and ammonium sulfate and diammonium sulfate can prevent the formation of such antagonistic salts, thereby forming glyphosate-NH4+ which is rapidly absorbed by plants. Phosphate, tartaric acid and ethylenediaminetetraacetic acid all increase the activity of glyphosate.
Surfactants should be given full attention in glyphosate formulations. Silicone surfactants have been designated as essential additives for glyphosate in New Zealand. They induce glyphosate to be quickly absorbed by plants through the pores, avoiding rainwater leaching and significantly improving herbicidal effects. Recently, the US EPA accepted IV-acyl sarcosine (methyl methamine) and IV-acyl sarcosine sodium salt surfactants produced by Hampshire Chemical Company as auxiliaries in the processing of glyphosate formulations, which are superior to Most surfactants are available.
In the transgenic glyphosate resistant crop field, glyphosate can be processed into a mixture or mixed with the herbicide variety used in the crop depending on the crop species. At present, glyphos-based mixtures mainly include (g/l): FallowStar [glyphosate + dicamba], Backdraft [glyphosate + imidazoquinoic acid (imazaquin)] (149+178) ,Extreme [glyphosate + imidazolium yoghurtyr] (238+258), Staple Plus [glyphosate + pyrithiobac] (40.2+1.7), Campaign and Lamdmater (glyphosate +2,4 -D) (108 + 192), Fidlemaster (acetochlor + atrazine + glyphosate) (240 + 180 + 90) and Ready Master ATZ (atrazine + glyphosate) (240 + 180) and the like.
2 Characteristics of glyphosate 2.1 Unique target and mechanism of action Unlike all current herbicide varieties, glyphosate has its unique target and mechanism of action. Glyphosate is an inhibitor of amino acid biosynthesis and its primary target is 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the shikimate pathway. Because of the inhibition of EPSPS, it is catalyzed by phosphoenolpyruvate (PEP) and shikimate-3-phosphate (S3P) to 5-enolpyruvylshikimate-3-phosphate. The conversion process of (5-enolpyruvylshikimate-3-phosphate, EPSP) is stopped, thereby inhibiting the biosynthesis of aromatic amino acids.
In plants, EPSPS is mainly found in chloroplasts and plastids. When glyphosate is present, glyphosate preferentially binds to the active site of EPSPS, causing the latter to undergo structural changes, thereby inhibiting its binding to PEP. And subsequent biocatalytic reactions.
This unique target and mechanism of action of glyphosate derives many other properties and its low toxicity to animals, such as its broad spectrum of herbicides, which are not easily resistant to weeds and to animals. Low toxicity and so on.
2.2 Good systemic and extremely broad herbicidal spectrum Glyphosate is a systemic herbicide that can absorb the drug in the green part of the plant. It can be absorbed down by stems and leaves, killing the underground rhizomes of perennial deep-rooted plants; it can also be transmitted between different tillers of the same plant, killing tillers or branches that are not exposed to the agent. Glyphosate is a broad-spectrum herbicide that can effectively control all annual and perennial grasses, dicotyledonous weeds and shrubs. It can kill the world's top ten perennial deep-rooted weeds.
2.3 Weeds are not susceptible to drug-resistant weeds, and they are also resistant to drugs, just like pests and diseases. In recent years, this problem has become increasingly serious. Resistance weeds were first reported in 1982, when only 30 weeds developed resistance. In 1990, it increased to 100 species. In 1999, it increased to 171 species, involving herbicides with different mechanisms of action. Among them, anti-ALS inhibitors have the fastest growth in killing grass, ranking first among resistant weeds. Accounted for 26%.
Glyphosate is outstanding in this regard. Although it has been widely used for a long time in nearly 30 years, only a few individual weeds are resistant to it. This feature is quite valuable. The reason is first related to its unique target and mechanism of action.
2.4 Friendly to human, ecological and environmental performance The common requirements of today's society in regulating human activities are human, ecological and environmentally friendly. Pesticides are no exception. Glyphosate is outstanding in responding to this requirement:
(1) It is a safe pesticide. The original drug has an oral LD50 of 4300 mg/kg in rats and a rabbit percutaneous LD50>5000 mg/kg. Its toxicity is classified as Class III according to WHO standard or EPA standard. That is, low toxicity.
(2) It is extremely toxic to mammals, birds and fish, has no teratogenicity, carcinogenicity and genotoxicity, and has no enrichment and accumulation in animals and aquatic organisms.
(3) Glyphosate and its metabolites are harmless to animals and microorganisms in the soil, and are low-toxic to bees.
(4) It is easy to adsorb to the soil, and basically has no migration, so it will not pollute the groundwater source. It is easy to be degraded by various microorganisms in the soil, and finally converted into inorganic phosphate, ammonia and CO2, etc., does not affect the soil structure, and does not remain in the soil to affect the post-crop crop.
(5) It is slowly metabolized to aminomethylphosphonic acid in plants.
3 Metabolism and degradation of glyphosate 3.1 Metabolism and degradation in plants Glyphosate is absorbed by the weed layer of weeds, which is accumulated in the upper part of the weeds through the symplast conduction, inhibiting arylalanine (phenylalanine) The biosynthesis of acid, tryptophan and tyrosine leads to the dysregulation of several metabolic reactions including protein synthesis and sub-production, as well as the resistance of shikimate synthesis pathway. The target of this is three: plastid EPSP synthase, cytoplasmic EPSP synthase and Cytosolic 3-deoxy-D-arabino-heptanone-7-phosphate synthase. It has been shown that glyphosate is metabolized by weeds through two pathways similar to microbial degradation. One is the oxidative cleavage of the CN bond to produce AMPA, and the other is that the CP bond is decomposed by CP lyase to produce methyl glycine; the metabolite AMPA is miscellaneous. Grass is toxic, but its activity is significantly lower than glyphosate.
3.1 Metabolism and degradation in the environment Microbial degradation is the main reaction of glyphosate in soil transformation. In the natural environment, especially in the soil where herbicides such as glyphosate are used for a long time, there are a wide variety of bacteria that can tolerate or degrade glyphosate. The degradation of glyphosate in soil is extensive and rapid. The study found that there are two main degradation pathways of glyphosate, CN breaks to form aminomethylphosphonic acid (AMPA) and CP bonds break to form sarcosine. These two intermediate metabolites are further metabolized to phosphoric acid, glycine, carbon dioxide, etc. to provide a source of phosphorus, carbon or nitrogen to the bacteria. The types of degrading microorganisms mainly include Pseudomonas, Pseudomonas, Penicillium, Thermophilus, etc. These microorganisms can grow with glyphosate as the sole source of phosphorus.
Among the two degradation pathways of glyphosate, most of the microbial degradation intermediates are AMPA and are carried out in the form of co-metabolism, that is, some bacteria degrade glyphosate to AM PA and others completely degrade AMPA. Pseudomonas, Flavobacterium, Arthrobacter, Klebsiella pneumoniae, etc. have been reported to rapidly degrade glyphosate into a non-toxic product AMPA through its metabolic activities, and the resulting phosphate can be utilized by a large number of microbial metabolism. . The scientists isolated 7 symbiotic nitrogen-fixing rhizobium bacteria capable of degrading glyphosate, such as Rhizobium meliloti, Rhizobium pea, Rhizobium natto, Rhizobium clover, Agrobacterium rhizogenes and Agrobacterium tumefaciens. This type of symbiotic rhizobium is required for growth of glyphosate as the sole source of phosphorus. It has C-P lyase (phosphonoacetate hydrolase) activity, which can interrupt the carbon-phosphorus bond in glyphosate to form a metabolic intermediate sarcosine. (N-methylglycine). Another report, Pseudomonas sp. And Arthrobacter sp. has a CP bond cleavage pathway.
In a complex forest ecosystem, glyphosate quickly disappears through a combination of dilution, conduction and biodegradation. (1) in rivers and slow-flowing ponds, through dilution and rapid disappearance in combination with soil, half-life <10h; (2) slow disappearance in ponds when climate is cold and microbial activity is low; (3) glyphosate Closely combined with the soil, it disappears rapidly; (4) The residual level of forest leaves is the highest, but it decreases rapidly. The moist conditions are favorable for the rapid decomposition of glyphosate in the leaves.
The method of using glyphosate indicates that the residual period of glyphosate in the soil is short. Glyphosate is widely used in pre-emergence or post-emergence seedlings. The conventional dose of glyphosate has no effect on crop growth, and does not harm insects, mites and microorganisms in the soil. Weeds can also germinate in the treatment area. Growing. American scientists conducted 13 tests in 47 different locations in 5 countries to determine the half-life of glyphosate. The test results showed that the half-life of glyphosate was 32 days. These locations include simple ecosystems such as farmland and complex forest ecosystems. This shows that glyphosate can quickly disappear from the environment under different soil and climatic conditions. In 2002, the European Union completed an assessment report on the environmental fate of glyphosate, indicating that the half-life of glyphosate averaged 30 days in wide-area climate conditions such as the United States, Canada and the European Union.
Glyphosate is easily adsorbed by organic matter and mineral clay. Once it touches the soil surface, it will bind tightly with the soil particles. Therefore, in most soils, the herbicidal ability of glyphosate is very weak. In the current study, glyphosate has not been found to move in the soil and therefore cannot penetrate into the untreated area. Glyphosate in soil and water does not move due to microbial degradation. When contacted with plant stem fluid, it is rapidly absorbed and transmitted through the symplast to various parts of the plant. Studies have also shown that glyphosate is safe for mammals, birds and fish and does not show signs of accumulation in the food chain. The toxic effects of glyphosate on aquatic organisms and environmental safety test results show that glyphosate is safe for fish and algae during normal application and weeding in water, but may have a slight effect on leech, but after 6 days of application The residue of glyphosate in the water basically disappears, and the water pupa is recovered at a faster rate, and its effect can be recovered in a short period of time.
4 Expanding the use of glyphosate Glyphosate is a systemic, conductive, and herbicide herbicide. Because it is not selective, it is widely used in non-farm, orchard, roads, forestry, etc. is too big.
Spraying before and after emergence of less tillage and no-tillage crops to prevent weeds from being produced, the dosage (0.20-2.24) kg/hm2. Ornamental plants, woody plants and vineyard weeds are sprayed after emergence, and control annual and perennial weeds. They are important herbicides in rubber gardens and orchards, and the dosage is (0.85~4.2) kg/hm2. When the protective spray is higher than 25 to 30 cm in height of corn, sorghum, soybean, etc., a protective cover is attached to the sprayer to spray, so that the liquid droplets do not contact the crop and are sprayed on the weed plants. In addition, this spray method can also be used to control weeds in rice fields.
Sugar cane sugar: Spraying low-dose glyphosate 10d-15d before sugarcane harvest can increase the sucrose content in sugarcane.
Crop drying and ripening: mainly used in wheat, corn, soybean and cotton crops, usually sprayed around 10d ~ 15d before harvest, wheat, corn dosage (0.25 ~ 0.85) kg / hm2, cotton dosage (0.85 ~ 4.0) ) kg / hm2. In the northeastern part of China, due to the short growth period, the water content of the grain is high when the crop is harvested, and the phenomenon of so-called “water glutinous rice†appears. Spraying glyphosate will help solve this problem.
Inhibition of forage growth and improved feed quality: application of glyphosate inhibited Agrostis spp. heading and reduced dormancy, increased edible and dry matter and protein content; inhibited Poa pratensis, Growth of Paspalum spp., Festuca ovina, Cynodon daclon, etc. Improve feed quality, usually in the amount (0.1 5 ~ 0.20) kg / hm2.
Review on the characteristics, safety and application of glyphosate