Herbicides generally used to kill weeds or unwanted plants. They are beneficial to get rid of those weeds but are very toxic to other organisms present in that respective ecosystem. Toxicity of chemicals vary from chemical to chemical and also depend on the dosage of the herbicides and mode of application, time of application etc.

1. HERBICIDES: CHEMICAL PROPERTIES AND USES
RABIYA BASRI
ALIGARH MUSLIM UNIVERSITY

2. 2, 4 – D – 2, 4 – DIPHENYL PHENOXY ACETIC ACID
 Herbicide and plant growth regulator
 Formulations include esters, acids, and several salts, which vary in their chemical properties, environmental
behavior, and to a lesser extent, toxicity.
 International Union of Pure and Applied Chemistry (IUPAC) chemical name for the acid form is 2,4-
dichlorophenoxyacetic acid, its Chemical Abstracts Service (CAS) registry number is 94-75-7, and the
chemical family is the phenoxy acetic acid compounds.
 Agent Orange, the herbicide widely used during the Vietnam war, contained 2,4-D. However, the
controversy regarding health effects centered around the 2,4,5-T component of the herbicide and its
contaminant, dioxin.
 2,4-D has been used in the United States since the 1940s, and it was evaluated for re-registration in 2005 by
the United States Environmental Protection Agency (U.S. EPA).
 U.S. EPA determined that 2,4-D was eligible for re-registration, but required certain changes to labeled uses
to mitigate risk.

3. 2, 4 – D - Properties
Class: Phenoxy
Molecular formula - C8H6Cl2O3 / Cl2C6H3OCH2COOH
Appearance: white to yellow powder
Molecular Weight: 221.03 g/mol
Trade name: 2, 4 – D, Fernoxone
Boiling Point: 160 °C (320 °F; 433 K) 0.4 mm Hg
Melting point: 140.5 °C (284.9 °F; 413.6 K)
Chemical names:
a) 2,4-dichlorophenoxyacetic acid 94-75-7
b) 2-(2,4-dichlorophenoxy)acetic acid
c) 2,4-D (2,4-Dichlorophenoxy)acetic acid

4. USES - 2, 4 – D
 2,4-D is used for broadleaf weed control in agricultural and nonagricultural settings, and it is registered for
use in both terrestrial and aquatic environments.
 Major sites include pasture and rangeland, residential lawns, roadways, and cropland.
 Crops treated with 2,4-D include field corn, soybeans, spring wheat, hazelnuts, sugarcane, and barley.
 Uses for products containing 2,4-D vary widely. Always read and follow the label when applying pesticide
products.
 Signal words for products containing 2,4-D may range from Caution to Danger. Signal word reflects the
combined toxicity of the active ingredient and other ingredients in the product.

5. Mode of Action for target organisms:
 2,4-D is used on a wide variety of terrestrial and aquatic broadleaf weeds. It has little effect on grasses.
 It appears to work by causing uncontrolled cell division in vascular tissue.
 Abnormal increases in cell wall plasticity, biosynthesis of proteins, and production of ethylene occur in
plant tissues following exposure, and these processes are responsible for uncontrolled cell division.
 Ester forms of 2,4-D penetrate foliage, whereas plant roots absorb the salt forms. 2,4-D appears to be
similar in action to other auxin-type herbicides.

6. ATRAZINE
 It was first registered for use in 1958
 Atrazine, also known as aatrex or gesaprim, belongs to the class of organic compounds known as
chloro-s-triazines.
 Atrazine is a member of the triazine chemical class, which includes simazine and propazine.
 These are aromatic compounds containing a 1, 3, 5-triazine ring that is substituted at the 2-position
with a chlorine atom.
 Atrazine exists as a solid and is considered to be practically insoluble (in water) and relatively neutral.
 Atrazine participates in a number of enzymatic reactions. In particular, atrazine can be biosynthesized
from 6-chloro-1, 3, 5-triazine-2, 4-diamine.
 Atrazine can also be converted into 4-ethylamino-6-isopropylamino-1, 3, 5-triazin-2-ol.
 Atrazine is an herbicide that does not occur naturally.
 Pure atrazine is an odorless, white powder that is not very volatile, reactive, or flammable and that will
dissolve in water.

7. Atrazine - Properties
Molecular Formula: C8H14ClN5
Appearance: colorless solid
Class: Triazine
Trade name: Aatres; Gesprim
Molar mass: 215.68 g/mol
Melting point: 175 °C
Boiling point: 200 °C
Soluble in: Water 7 mg/100 mL
Density: 1.187 g/cm3
Chemical names: a) 1-Chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine
b) 2-Chloro-4-ethylamino-6-isopropylamino-s-triazine
c) 6-Chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine

8. USES - Atrazine
 Atrazine is used to kill weeds, primarily on farms, but has also been used on highway and railroad rights-
of-way.
 EPA now restricts how atrazine can be used and applied; only trained people are allowed to spray it.
 Atrazine is a widely used herbicide that can be applied before and after planting to control broadleaf and
grassy weeds.
 It is used in primarily in agriculture, with the greatest use on corn, sorghum, and sugarcane.
 To a lesser extent, it is used on residential lawns and golf courses.

9. Mode of Action for target organisms:
 Atrazine interferes with photosynthesis in some broadleaf plants and grasses.
 It is taken up by roots and leaves and moves upward in the plant to areas of new growth.
 Plant dries out and dies.
 Older leaves on plants may be affected more than new leaves.
 Root growth is not affected by atrazine.

10. GLYPHOSATE
 It is a broad-spectrum systemic herbicide and crop desiccant. It is a phosphonic acid and
a glycine derivative.
 It is a conjugate acid of a glyphosate(2-) and a glyphosate(1-).
 Glyphosate is a phosphonic acid resulting from the formal oxidative coupling of the methyl group of methyl
phosphonic acid with the amino group of glycine.
 It is one of the most commonly used herbicides worldwide, and the only one to target the enzyme 5-
enolpyruvyl-3-shikimate phosphate synthase (EPSPS).
 It has a role as an agrochemical, an EC 2.5.1.19 (3-phosphoshikimate 1-carboxyvinyltransferase) inhibitor.
 Glyphosate is an odorless white powder. Decomposition begins at approximately 419°F (darkens). pH (1%
solution in water) 2.5.

11. Molecular Formula: C3H8NO5P
Appearance: white crystalline powder
Molar mass: 169.073 g·mol−1
Class: Aliphatics
Melting Point: 184.5 °C (364.1 °F; 457.6 K)
Boiling Point: 187 °C (369 °F; 460 K) decomposes
Chemical name: [(phosphonomethyl)amino]acetic acid
Trade name: Round up, Glycel
Molar mass: 169.07 g/mol
Density: 1.7 g/cm³
Solubility in water: 1.01 g/100 mL (20 °C)

12. USES - Glyphosate
 Glyphosate products are one of the most widely used weed killers worldwide in farms and in home gardens
and lawns. It is effective at managing invasive and noxious weeds.
 These products typically contain glyphosate in combination with other ingredients that help improve the
absorption of the glyphosate into the plant.
 Glyphosate targets a broad range of weeds and is important in the production of fruits, vegetables, nuts, and
glyphosate-resistant field crops such as corn and soybean.
 In addition, glyphosate breaks down in the environment, can be used for no-till and low-till farming which
can reduce soil erosion, and is useful for integrated pest management.
 Products containing glyphosate are sold in various formulations, including as liquid concentrate, solid, and
ready-to-use liquid.

13.  Glyphosate is used in products such as Roundup® to control weeds in both agricultural and non-
agricultural settings.
 It can be applied in agricultural, residential and commercial settings using a wide range of application
methods, including aerial sprays, ground broadcast sprayers of various types, shielded and hooded
sprayers, wiper applicators, sponge bars, injection systems, and controlled droplet applicators.
 Agricultural uses include corn, cotton, canola, soybean, sugar beet, alfalfa, berry crops, brassica
vegetables, bulb vegetables, fruiting vegetables, leafy vegetables, legume vegetables, cucurbit
vegetables, root tuber vegetables, cereal grains, grain sorghum, citrus crops, fallow, herbs and spices,
orchards, tropical and subtropical fruits, stone fruits, pome fruits, nuts, vine crops, oilseed crops, and
sugarcane.
 Nonagricultural uses include conservation land, pastures, rangeland, aquatic areas, forests, turf grass,
residential areas, non-food tree crops (e.g., pine, poplar, christmas trees), rights of way, commercial
areas, paved areas, spot treatments, ornamentals, parks, and wildlife management areas.

14. Mode of Action for target organisms:
 In plants, glyphosate disrupts the shikimic acid pathway through inhibition of the enzyme 5-
enolpyruvylshikimate-3-phosphate (EPSP) synthase. The resulting deficiency in EPSP production leads to
reductions in aromatic amino acids that are vital for protein synthesis and plant growth.
• Glyphosate is absorbed across the leaves and stems of plants and is translocated throughout the plant. It
concentrates in the meristem tissue.
• Plants exposed to glyphosate display stunted growth, loss of green coloration, leaf wrinkling or
malformation, and tissue death. Death of the plant may take from 4 to 20 days to occur.
• Sodium salt of glyphosate can act as a plant growth regulator and accelerate ripening of specific crops.

15. BUTACHLOR Butachlor is a herbicide of the acetanilide class.
USES:
 It is extensively used in India in the form of granules in rice as post emergence herbicide.
 Used pre-emergence for the control of annual grasses and certain broad-leaved weeds in rice, both
seeded and transplanted. It shows selectivity in barley, cotton, peanuts, sugar beet, wheat and several
brassica crops.
 Use @ 1.25 Kg/ha
Formulation types EC; GR.
Selected tradenames: 'Machete' (Monsanto); 'Butanex' (Makhteshim-Agan); 'Butataf' (Rallis); 'Dhanuchlor'
(Dhanuka); 'Farmachlor' (Sanonda); 'Hiltaklor' (Hindustan); 'Rasayanchlor' (Krishi Rasayan); 'Trapp'
(RPG); 'Wiper' (Nagarjuna Agrichem)

16. Butachlor
Molecular Formula: C17H26ClNO2
Appearance: Light yellow oil
Molar mass: 311.85 g·mol−1
Class: Aliphatics
Melting Point: -0.55 oC
Boiling Point: 156 oC
Chemical name: N-(Butoxymethyl)-2-chloro-N-(2,6-diethylphenyl)acetamide
Trade name: Machette
Density: 1.0695 g/cm3
Solubility in water: 20 mg/L (20 °C)

17. Mode of Action to target organisms:
 Inhibits cell division by blocking protein synthesis.
 Selective systemic herbicide, absorbed primarily by the germinating shoots, and secondarily by the
roots, with translocation throughout the plant, giving higher concentrations in vegetative parts than in
reproductive parts. Effective rates range from 1.0-4.5 kg a.i./ha.
 Activity is dependent on water availability such as rainfall following treatment, overhead irrigation or
applications to standing water as in rice culture.
 Phytotoxicity Non-phytotoxic to rice, cotton, barley, wheat, peanuts, sugar beet, and some brassicas.

18. BENTHIOCARB
 Benthiocarb is a thiocarbamate, cholinesterase inhibitor used as an herbicide.
 Selective for rice
 It doesn’t inhibit the seed germination but inhibits elongation of germinated seeds.

19. Benthiocarb
Molecular Formula: C12H16ClNOS
Appearance: Pale yellow brownish color liquid
Class: Aliphatics
Melting Point: 3.3 °C (37.9 °F; 276.4 K)
Boiling Point: 126 to 129 °C (259 to 264 °F; 399 to 402 K)
Chemical name: S-(4-Chlorobenzyl) diethylcarbamothioate
Trade name: Thiobencarb, Bolero and Saturn
Molar mass: 257.780
Density: 1.145-1.80 g/cm3 at 20 oC
Solubility: Acetone, ethanol, xylene, methanol, benzene
(Solubility in water @ 28.0 mg/L at 25 °C)

20. Thank you