Herbicides classification,their development history and mode of action of Herbicides.pptx

Herbicides Classification,their development history and mode of action of Herbicides

1. BTC College of Agriculture and Research Station, Bilaspur . Assignment On – 2022-23 Topic – Herbicides Introduction and History of their Development, Classification Based on Chemical, Physiological Application and Selectivity, Mode and Mechanism of Action of Herbicides Course Title - Weed Management Course No. - AGRON- 503 Credit Hours - 2+1 Year - M.Sc. 1 st year & 1 st Sem. Department - Agronomy Submitted To - Submitted By - Dr. T.D. Pandey Mohan Sahu Scientist (Department of Agronomy) M.Sc. 1 st Year & 1 st Sem.

2. Herbicide Introduction Herbicide, derived from Latin word herba (plant) and c aeder (to kill), means chemicals that kills or suppress the unwanted vegetation Weedicide it was restricted term chemicals that kills the weeds only Herbicides are chemicals capable of killing or inhibiting the growth of plants. Herbicide, an agent, usually chemical, for killing or inhibiting the growth of unwanted plants,  

3. History of their Development Before 1940 the era of inorganic herbicides like- Ashes,salts, copper sulphate, sodium Arsenate, sodium nitrate, sodium chloride, etc Era of Organic herbicides was started with the discovery of 2,4-D ( dichloro phenoxy acetic acid) in 1940 (used as a plant hormone). Hammer and Turkey 1944 firstly observe the 2,4-D successful controlled weeds in cereal crops.

4. 2,4-D is the first selective organic herbicide used in the world. Revolution in weed control by discovery of 2,4-D ( in pokorny ) 1944. In India 2,4-D 1 st tested is the herbicides in 1946 and introduced it commercially in field level in 1948. Herbicides are registered in India under the insecticides act 1968 at present October(2015) 60 technical herbicides and 17 herbicide premixes have been registered for use. In India the Central insecticide board and registration committee (CIBRC) regulates and manages the use of herbicides and insecticides In India share of herbicides is only 8% of the total pesticides consumed. Average herbicide using India is 40 gram/ hectare/year, 675-1350 gram/hectare/year in advanced countries.

5. The major crops we are maximum herbicides are used are rice, wheat and plantation crops. The state where highest herbicides are used his Punjab followed by Andhra Pradesh and Uttar Pradesh. The mostly used herbicides in India are isoproturon , butachlor ,2,4-D,glyphosate and atrazine. Herbicide conception position in world- herbicide> insecticide > fungicide Herbicide consumption position in India- insecticide> fungicide >herbicide. Directed of wheat research is in Jabalpur in Madhya Pradesh.

6. Classification Based on Chemical Inorganic Herbicides – Copper sulphate ( CuSo4) was the earliest inorganic salt used as a selective herbicide for controlling dicot weeds in cereal crops during 1896 in France, Germany and USA. Sulphuric acid (H2SO4) was used as a herbicide in cereals during 1909. Sodium chloride( NaCl ) under the name moth herbs in used in France for killing deep rooted perennials. Another non select your beside ammonium sulphate was introduced in 1945 is a mate for the control of woody plants .

7. Organic Herbicides Organic Herbicides are more Effective and Selective . Chemical Group Herbicides Sulphonyl ureas Sulphosulphuron , chlorimuron - ethyl , metasulphuron - ethyl. Amide Alachlor , Butachlor , propanil . Bipyridiums Paraquat , Diquat . Dinitroanilines Fluchloralin , Pendamethalin . Triazines Atrazine , Simazine.

8. Chloro phenoxy compound 2,4-D , 2,4,5-T ,MCPA ,2,4-DB Ureas Monuron,Diuron , Imidazolines Imazathayper,Imazaquin,Imazapic Organophosphate Glyphosate,Anilophos . Phenoxy phenoxy alkanoic Acids Clodinafop , Fenoxaprop -p- ethyle , Substituted Urea Diuron , Linuron , Isoproturon,Metaxuron Aliphatics TCA, Dalapon,Acrolein Benzoic acids Dicamba , Amiben , Chloramben Oxadiazoles Oxadiazon Phenylpyridazones Sulfentrazone Piclonic Acids pyridine Picloram , Dithiopyr , Fluridone . Cineoles Cinmethylin Others Pichloram , Pyrazon , Oxadiazon , Amitrole

9. Based on Physiological Application Soil applied herbicides:   Herbicide act through root and other underground parts of weeds.  1. Soil Surface Application- Applied on surface by broadcasting and Spraying. Eg.Triazines , Trifluralin 2. Sub- Surface Application- In 7-10 Cm.below the soil surface. Eg.Fluchloralines 3. Band application- Application to restricted band along the crop rows, Eg . Atrazine in maize. 4. Soil fumigant – Release in Gaseous form in the soil Eg.Methyl bromide.

10. Foliage Applied H erbicides   Herbicide primarily active on the plant foliage Eg.Glyphosate , Paraquat . 1. Blanket Application – Uniform application of herbicide to standing crops. Eg.2,4-D in wheat, MCPB in Pea. 2. Directed Application – Application of herbicide to eats which are growing in the inter rows of crop. 3. Spot Treatment – Application of herbicides to small Patches of weeds. 4.Protected Spraying- Non selective herbicides can be employed to obtain . selective wheat control in wide distant crop, covering the non target plants before application of the Herbicide

11. Based on Selectivity Selective Herbicides – Selected to particular species - Eg.2,4-d, atrazine, EPTC, Tryfluralin , Alachlor , Butachlor , pendimethylene are selective Herbicides used in crop land. Non- Selective Herbicides- It is one that kills plants without regard to species, example . paraquat , Diquat , Glyphosate ,sodium chlorate , weed oils .

12. Mode of Action of Herbicides The term mode of action refers to the sequence of events from absorption into plants to plant death. The mode of action of the herbicide influences how the herbicide is applied. For example, contact herbicides that disrupt cell membranes, such as Acifluorfen (Blazer) or Paraquat ( Gramoxone Extra), need to be applied post emergence to leaf tissue in order to be effective. Seedling growth inhibitors, such as trifluralin ( Treflan ) and Alachlor (Lasso), need to be applied to the soil to effectively control newly germinated seedlings. To be effective, herbicides must 1) adequately contact plants; 2) be absorbed by plants; 3) move within the plants to the site of action, without being deactivated; and 4) reach toxic levels at the site of action. The application method used, whether pre plant incorporated, pre emergence, or post emergence, determines whether the herbicide will contact germinating seedlings, roots, shoots, or leaves of plants.

13. The herbicide families listed below are grouped on the basis their mode of action 1. The Growth Regulator Herbicides (2,4-D, MCPP, Dicamba , and Triclopyr ) . These are mostly foliar applied herbicides which are systemic and translocate in both the xylem and phloem of the plant. They mimic natural plant auxins , causing abnormal growth and disruption of the conductive tissues of the plant. The injury from this family of herbicides consists of twisted, malformed leaves and stems.

14. 2. The inhibitors of amino acid synthesis (Glyphosate, Halosulfuron , Imazethapyr , and Sulfometuron ).  Both foliar and soil applied herbicides are in this family. Glyphosate translocates in the phloem with photosynthates produced in the leaves. Others in this family move readily after root or foliar absorption. These herbicides inhibit certain enzymes critical to the production of amino acids. Amino acids are the building blocks of proteins. Once protein production stops, growth stops. Symptoms are stunting and symptoms associated with lack of critical proteins

15. 3. Cell membrane disrupters  - with soil activity ( oxyfluorfen , lactofen , and acifluorfen ). Soil and foliar applied with limited movement in soil. These herbicides enter the plant through leaves, stems, and roots, but are limited in their movement once they enter the plant. Membrane damage is due to lipid peroxidation. Symptoms are necrosis of leaves and stem. .

16. 4. Lipid biosynthesis inhibitors ( diclofop , fluazifop , sethoxydim , and clethodim ).  Foliar applied Diclofop has both soil and foliar activity. Herbicides in this family move in both the xylem and phloem of the plant and inhibit enzymes critical in the production of lipids. Lipids are necessary to form plant membranes which are essential to growth and metabolic processes. Symptoms include stunting and death of tissue within the growing points of plants.

17. 5. Pigment inhibitors ( norflurazon , fluridone , and amitrol ).  Soil applied and move in the xylem except amitrol , which moves in both phloem and xylem. These herbicides inhibit carotinoid biosyntehsis , leaving chlorophyll unprotected from photooxidation . This results in foliage which lacks color. Symptoms include albino or bleached appearance of foliage.

18. 6. Growth inhibitors of shoots ( thiocarbamate herbicides including: EPTC, cycloate , pebulate , and molinate ).  Soil applied and somewhat volatile, requiring incorporation. Enter the plant through the roots and translocated through the xylem with the transpiration stream to the growing points in the shoot. Mode of action is unclear, but affects developing leaves in growing points of susceptible plants. Symptoms include stunting and distortion of seedling leaves. 7. Herbicides which disrupt cell division ( trifluralin , DCPA, Dithiopyr , Oryzalin , Pronamide , Pendimethalin , and Napropamide ). All are soil applied, with limited movement in the soil. Absorbed through roots or emerging shoot tips. Once absorption takes place, movement is limited (site of action is near the site of absorption). These herbicides inhibit cell division or mitosis, except pronamide and napropamide which stop cell division before mitosis. Symptoms include stunting and swollen root tips

19. 8. Cell membrane disrupters - no soil activity ( Paraquat , Diquat , Glufosinate , acids, oils, soaps). These herbicides are foliar applied with no soil activity. They enter the plant through the leaves and stems and do not move significantly within the plant once absorbed. These herbicides either act directly on cell membranes (acids, soaps. oils) or react with a plant process to form destructive compounds which result in membrane damage. Symptoms include rapid necrosis of the leaves and stem. 9. Inhibitors of photosynthesis ( Atrazine , Simazine , Metribuzin , Cyanazine , Prometryn , Diuron , Linuron , Tebuthiuron , and Bromocil ).  These are soil applied herbicides, however, all except Simazine also have foliar activity. They move readily in the plant in the xylem with the transpiration stream where they concentrate in the leaves at the site of photosynthesis. Once there they block the electron transport system of photosynthesis, causing a build up of destructive high energy products which destroy chlorophyll and ultimately the leaf tissues. Symptoms include chlorotic (yellowed ) leaves which become necrotic.

20. Reference – Reddy, S.R. (2019). Principles of Agronomy, Kalyani Publication, Ludhiana. Das T.K. (2016). Weed Science Basics and Application, Jain Brothers, New Delhi. https://www.intechopen.com/chapters/49524 https://extension.okstate.edu/fact-sheets/herbicide-how-to-understanding-herbicide-mode-of-action.html .