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Classification of herbicides.pptx

  1. 1. Presented by: Uday Kumar Lodh M.Sc. Forestry (Plantation Technology) ICAR JRF (AIR-2)
  3. 3. WHAT ARE PESTICIDES?? • Substances meant for attracting, seducing, and then destroying any pest. • They are a class of biocide. • The most common use of pesticides is as plant protection products (also known as crop protection products), which in general protect plants from damaging influences such as weeds, fungi, or insects. • Use of pesticides is so common that the term pesticide is often treated as synonymous with plant protection product. • It is in fact a broader term, as pesticides are also used for non-agricultural purposes.
  4. 4. The Food and Agriculture Organization (FAO) has defined pesticide as: • Any substance or mixture of substances intended for preventing, destroying, or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals, causing harm during or otherwise interfering with the production, processing, storage, transport, or marketing of food, agricultural commodities, wood and wood products or animal feedstuffs, or substances that may be administered to animals for the control of insects, arachnids, or other pests in or on their bodies.
  5. 5. World scenario Indian scenario
  6. 6. Facts about pesticides and herbicides • Largest consumption of herbicides is in wheat followed by rice and tea. • The largest manufactured and consumed herbicides in india is isopruton. • Per hectare consumption of pesticide in India is less than 0.5kg/ha. • Highest consumption of pesticides in the world is Japan (10-12 kg/ha). • Herbicide consumption in India is 40g/ha. •The largest pesticide consuming crop in india is cotton followed by rice and vegetables.
  7. 7. CLASSIFICATION OF HERBICIDES A) Selective herbicides :- One that kills only targeted weeds e.g., • Simazine • Atrazine • 2,4-D • MCPA (2-methyl,4- chlorophenoxy acetic acid) • Butachlor • Pendimethalin On the basis of selectivity
  8. 8. B) Non-selective herbicides :- Kills all vegetation (crop + weed) without the regard of species e.g, • Diquat • Paraquat • Sodium chlorate • Weed oils  However selectivity depends on dosage of herbicides for ex.. Simazine and diuron acts as Non-selective herbicides when applied at high rates.  Selective herbicidal control has reached such an advanced stage that weed of a grass family can be controlled in the crop of same family.. Ex avena
  9. 9. On the basis of Translocation A) contact herbicide :- Kills the vegetation either weeds or crops when it comes in contact e.g. • Paraquat • Diquat When applied to foliage it will not kill its roots, though in simple annuals the roots may die because they were deprived of their shoots
  10. 10. B) Systemic or translocated :- Moves within the plant from the point of treatment to its other parts and affect the whole system like photosynthesis and, • 2,4-D, • Atrazine  Important in controlling the perrenial weeds.  Can be applied in low volume sprays.  Some herbicides may exhibit both, contact and tranlocation activities. Ex., Atrazine
  11. 11. On the basis of its range A) Narrow spectrum herbicides : when applied to a mixed population of weeds, proves active on one or limited species. • Useful against specific noxious weeds. • Eg ., Metoxuron, Difenzoquat and Diclofop are widely used against specific weeds like phalaris minor and avena fatua. • There is need to employ additional herbicides to control mixed weed species.
  12. 12. B) Broad spectrum herbicides : control weed species belonging to different classes at a time.
  13. 13. On the basis of time of application A) Pre-plant applied : such herbicides are applied before planting of crop in the field e.g. Fluchloralin & Alachlor. B) Pre-emergence : applied before emergence of weeds but post-emergence of crops e.g. only selective herbicides . C) Post-emergence: applied after the emergence of weed and crop e.g. 2,4-D , Propanil, Diquat,Dalapon.
  14. 14. On the basis of method of application A) Soil applied herbicides: primarily applied to soil rather than vegetation .  Inside soil it kills weeds as they germinate & inhibits sprouting of rhizomes, stolons and tubers.  It eliminates early weed competition for period it remains active in soil (4-8 weeks).  Largely applied at the time of at the time of planting of crops ex., simazine,alachlor,trifluralin
  15. 15. B) Foliage applied : applied to weeds after their emergence from soil.  They are absorbed by the plant foliage and translocated to other plant parts Most effective against young weeds in their seedling stage but at high rates may kill established weeds ex., paraquat ,Diquat & MCPB(2-methyl,4- chlorophenoxy butyric acid).
  16. 16. c) Aquatic application • Chemicals specifically formulated for use in water to kill or control aquatic plants. • They are sprayed directly onto floating or emergent aquatic plants or are applied to the water in either a liquid or pellet form. Ex. Copper sulphate , 2,4-D.
  17. 17. On the basis of its residual effect A) Residual herbicide: Maintains its phytotoxic effects in soil for considerable time after its application.  Residue period may be 3-4 weeks in some herbicide (2,4-D & EPTC) and much longer in others. B) Non-residual herbicides : It is inactivated in soil immediately in few days after it reaches the soil. ex.. paraquat , diquat , amitrole  very short persistence herbicides for quick knock down of existing weeds
  18. 18. ON THE BASIS OF CHEMICAL STRUCTURE 1) Inorganic Herbicides: Contain no carbon atoms(such compounds may contain either C-H or C-C bonds, but not both) in their molecules. These were the first chemicals used for weed control before the introduction of the organic compounds. a) Acids: Arsenic acid, arsenious acid, arsenic trioxide & Sulphuric acid. b) Salts: Borax, copper sulphate, ammonium sulphate, Na chlorate , Sodium arsenite ,Copper nitrate.
  19. 19. 2) ORGANIC HERBICIDES • Contain carbon and hydrogen in their molecules. • Consists of 16 to 17 groups. • OILS: Diesel oil, standard solvent, xylene-type, aromatic oils etc.
  20. 20. GROUP HERBICIDES Aliphatics Dalapons , TCA(trichloro acetic acid) , acrolein Amides & acetamides Butachlor , alachlor ,propachlor, propanil Benzoics 2,3,6-TBA, Dicamba , Tricamba, Chloramben Bipyridiniums Paraquat , diquat Carbamates Propham , barban, dichlormate Thiocarbamates Butylate , thiobencarbe or benthiocarb Dithiocarbamates CDEC , metham Nitriles (benzonitrates) Bromoxylin , dichlobenil Dinitroanilines Fluchloralin(basalin) , pendimethalin, trifluralin, nitralin Phenols Dinoseb , DNOC , PCP Phenoxys 2,4,5-T ; MCPA; 2,4-DB ; Dichlorprop Triazines Atrazines , propazine, simazine ( soil applied) Ureas Diuron , monuron , isoproturon Uracils Bromacil , terbacil Diphenyl ethers Nitrofen (Toke – 25) Others Pichloram , pyrazon, glyphosate
  21. 21. 1) Aliphatic acids • Dalapon is active on plant shoots. • Maximum use is against grasses in jute, coffee, citrus, some stone fruits and under grape vines. • On non-crop land , combined with 2,4-d,dalapon (10-20kg) forms a very good general weed killer. • Split application has proved more effective on perennial grasses. • Persistence in soils is 2-4 weeks.
  22. 22. 2)Amides & acetamides • Principal use : selective pre-emergence control of annual grass & broad-leaf weeds. However propanil is used only post-emergence to the weeds & has no pre-emergence activity. • Mode of action :. They inhibit several metabolic process including lipid biosynthesis and synthesis of proteins and giberellins . Pronamide inhibits the mitosis activity (foliar applied). • Tranlocation : readily root absorbed and translocated • Common characteristics : * Do not control established weeds. * Readily leached in soils in rainfall condition. * It is soil applied. * soil persistence is 1-3 months . * Herbicides loss from soil is mostly by microbial action. Butachlor propanil
  23. 23. 3) Bypyridinium herbicides Two herbicides namely paraquat and diquat Also referred to as “quaternary ammonium herbicides” These herbicides are active as cations. Principle use : - Non selective, early post-emergence control of seedling grass and broadleaf weeds in croplands prior to crop planting or emergence. - paraquat is also a crop dessicant. -Diquat is principally used to control aquatic weeds in ponds ,lakes and ditches
  24. 24. Mode of action : These are post- emergent, contact-type herbicides,killing green tissue very rapidly. -These herbicidal activity is dependent on presence of light,oxygen,and photosynthesis - They are rapidly absorbed by green plant tissue and they interact with the photosynthetic process to produce superoxides, which destroy the plant cells.  Tranlocation : paraquat and diquat are not translocatedin plants  common characteristics : - They are photochemically degraded on plant surfaces . - they have no soil residue activity. - weed biotypes resistant to paraquat and diquat have occurred where these herbicides were applied repeatedly for 5 or more years
  25. 25. 4) Dinitroaniline herbicides • Pendimethalin, trifluralin,fluchloralin belong to this group. Principal use o Pre-emergence control of seedling grass , broadleaved weeds and corn fields. Mode of action  Inhibition of mitosis  Inhibit root and shoot development by interfering cell division in meristems  Adversely affect development of cell wall and membranes Translocation  Not tranlocated in plants after root or shoot absorption Selectivity • Should avoid contact with desired plants . Characteristics  Applied prior to weed seed germination  Have little or no post emergence activity  Lateral root development of crop plants (cotton and soybean ) is inhibited in soil treated with these herbicides.  Their soil persistence is about 6 months or less.
  26. 26. MoA: Microtubule assembly inhibition Chemistry: Dinitroaniline Herbicide: pendimethalin Symptoms: root malformation, root stunting, root thickening MoA: Microtubule assembly inhibition Chemistry: Dinitroaniline Herbicide: trifluralin Symptoms: leaf reddishness, root malformation, root stunting, root thickening, stunting
  27. 27. 5) Thiocarbamate herbicides Metham , Butylate , thiobencarbe or benthiocarb, EPTC(S-Ethyl dipropylthiocarbamate) Principal use • Used in pre-emergence control of annual grass weeds • Do not control established weeds • Metham ( dithiocarbamate used as nonselective soil fumigant to control weeds , insects , fungi) & also kill roots in sewer pipes. Mode of action  Inhibit lipid formation due to inhibition of acetyl-CoA. Translocation  Rapidly absorbed by roots and translocated upwards Selectivity  Selectivity is due to rapid molecular degradation of the herbicides by tolerant plants and failure of susceptible plants to do so.  Herbicide placement with respect to seed germination and seedling development Common charcteristics  Site of action is the developing shoot and coleoptile of grass seedlings.  Only control seedling grasses  Highly volatile therefore it is soil incorporated by tillage
  28. 28. Plant: alfalfa MoA: Inhibition of lipid synthesis Chemistry: Thiocarbamate Herbicide: EPTC Symptoms: leaf cupping, leaf curling, leaf distortion, leaf malformation, leaf stacking, stunting Plant: alfalfa MoA: Inhibition of lipid synthesis Chemistry: Thiocarbamate Herbicide: EPTC Symptoms: leaf distortion, seedling distortion, stunting
  29. 29. 6) Triazine herbicides Principal use  Used for selective pre-emergence and post- emergence control of seedling grass and broadleaved weeds.  Most effective in controlling the broadleaf weeds Mode of action  Inhibit photosynthesis by binding onto the pigment protein of the ps-II complex Tranlocation  Readily absorbed by plant roots and then translocated to the leaves via tranpirational stream  Applied post-emergence these are foliar-absorbed except for simazine. Selectivity  Achieved by their rapid detoxification by tolerant crop plants Common characteristics • Readily absorbed by both roots and foliage. • Do not control established annual or perennial or deep-rooted weeds applied at recommended dosages • They are readily absorbed to soil colloids and they resist leaching
  30. 30. 7) Urea herbicides Principal use  For selective pre-emergence and post-emergence control of weed grass and broadleaved weeds & also non-selective control of weeds in non crop areas. Mode of action  Inhibit photosynthesis by inhibiting Ps- II complex.  Secondary effects such as production of free radical are responsible for rapid plant kill. Selectivity  It is primarily due to herbicide placement rather than physiological tolerance of crop plants. Common charcteristics  Resistant weed biotypes of some species have developed by continuous use of these herbicides.  Low water soluble  Adsorbed to soil colloids and resist leaching  Generally applied to soil surface as pre- emergence treatment to the weeds
  31. 31. Other herbicides Glyphosate Used nonselective post-emergence control of annual, biennial and perennial grasses and aquatic weeds. Mode of action  . Primary mechanism of action of this foliage activity, wide-spectrum herbicide is inhibition of enzyme 5- endolpyruvylshikimate-3-phosphate synthase (EPSP) which is reponsible for synthesis of phenylalanine, tryasine and tryptophan  They also inhibit the synthesis of aminolevulinicacid (ALA), thereby blocking porphyrin ring synthesis and subsequently , all compounds normally containing porphyrin rings such as chlorophyll , cytochromes and peroxidases. Translocation  Following foliar application it is readily absorbed and translocated through aerial and underground plant parts. Selectivity  Achieved by use of directed or shielded spray to avoid contact with green stems and foliage.  They are strongly absorbed to soil colloids and have no soil activity
  32. 32. Picloram • It is persistent auxin like substance. • It stimulates cell elongation in the susceptible plants. • The affected plant exhibit epinasty and split-shoots due to tissue proliferation. • Leaves are puckered and cupped. • The roots deteriorate and die because of abraded development of vascular bundles. • It is reported to lower the nuclease enzyme activity, resulting in abnormally high nucleic acid content

Editor's Notes

  • in intensive crop rotations , usually herbicides with 3-6 rotations are used . Persistence of herbicide function of herbicide structure,rate,soil type,&climatic condition
  • primary mode of action of this group is not known except for pronamide