1.
Presented by:
Uday Kumar Lodh
M.Sc. Forestry (Plantation Technology)
ICAR JRF (AIR-2)

2.
CLASSIFICATION OF HERBICIDES

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.
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.
World scenario Indian scenario

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.
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.
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.
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.
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 respiration.eg.,
• 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.
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.
B) Broad spectrum herbicides : control weed
species belonging to different classes at a time.

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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