This document provides an introduction to weeds and weed management in rabi crops. It defines weeds and discusses their characteristics, impacts on crop production through competition and allelopathy. The principles and methods of weed control are explained, including preventive, mechanical, agronomic, chemical and integrated weed management approaches. Specific herbicides used in wheat, chickpea, lentil, field peas and mustard are also listed. The document covers weed identification, losses caused by weeds, herbicide formulations, modes of action, and development of herbicide resistance in weeds over time.

1. WELCOME

2. PRESENTED BY :- 66/AG/15
32/AG/15

3. INTRODUCTION
•RABI CROPS – These crops are generally planted in November &
harvested in April. For e.g. :- Wheat, Barley, Pea etc.
•WEEDS –
JETHRO TULL first coined the term “WEED” in 1931.
>A weed is a plant growing where it is not wanted.
> Weed is an unwanted plant that grow along with main crop in our
field.
> Weed is a plant that is extremely noxious, useless, unwanted,&
poisonous.
•WEED MANAGEMENT :- Weed management is the application of
certain principles & suitable methods that will improve the vigour &
uniform stand of the crop. At the same time ignores or discourage the

4. CHARACTERISTICS OF
WEED
1. In the world 30,000 species of weeds have been
listed.
2. Out of which 18,000 cause serious damage to
agricultural production.
3. 18 weeds are considered as world worst weeds.
4. These weeds are more competitive than
cultivated crops.
5. They are capable of thriving under stress
condition. They produce enormous seeds.
6. The weed seeds are easily germinated, they
undergo pollination very easily.

5. Avena fatua (wild oat) Medicago denticulata
(Burclover)
Cichorium intybus
(Chicory)

6. LOSSES CAUSED BY
WEEDS
• Reduce productivity
• Deplete nutrients and soil moisture
• Harbour insects, diseases and nematodes
• Reduce quality of produce
• Affect human and animal health
• Increase production and processing cost
• Reduce land value and choice of crops
• Invasive weeds endanger biodiversity
• Affect aquatic flora and fauna

7. YIELD LOSS FROM DIFFERENT
SOURCES
WEEDS
37%
INSECTS
29%
DISEASES
22%
OTHERS
12%
Weeds have serious impacts on agricultural production. It is
estimated that in general weeds cause 5% loss in agricultural
production in most of developed countries, 10% loss in less
developed countries and 25% loss in least developed countries

8. CROP WEED COMPETITION
AND ALLELOPATHY
Competition (Allelospoly): It is the relationship between two plants (weed/crop,
crop/crop, weed/weed) in which the supply of a growth factor falls below their combined
demand for normal growth and development. The growth factor competed include
water, nutrients, light, space and air/gasses (oxygen, carbon dioxide)
Types of competition:
• Above-ground (Aerial) competition : Takes place in the leaves and the growth
factors
involve are light and carbon dioxide.
• Below-ground competition: Takes place mainly in the roots while the growth factors
involve are water, nutrients and oxygen.
The perceived consequence of competition with crop is reduction in the economic
yield of
affected crop plants.
Forms of competition:
Intra specific competition: competition for growth factors among individuals of a plant
species

9. >CONTINUE
Competition and Allelopathy are the main interactions, which are of
importance between crop and weed. Allelopathy is distinguished from
competition because it depends on a chemical compound being added
to the environment while competition involves removal or reduction of
an essential factor or factors from the environment, which would have
been otherwise utilized.

10. PRINCIPLES & METHODS OF
WEED CONTROL
There are THREE main Principles of weed control.
> PREVENTION
> ERADICATION
> CONTROL
> MANAGEMENT
METHODS OF WEED CONTROL
• PREVENTIVE METHODS
• MECHANICAL & PHYSICAL METHODS
• AGRONOMICAL / CULTURAL / ECOLOGICAL METHODS
• CHEMICAL METHODS
• INTEGERATED WEED MANAGEMENT

11. PREVENTIVE METHODS
• Use of weed free seed for sowing
• Use of cleaned tillage and sowing implements
• Use of well decomposed manures
• Weed laws
• Seed laws
• Plant quarantine
• Cleaning of irrigation channels/canals
• Cleaning of bunds, roadsides, fences and non-
cropped area

12. MECHANICAL & PHYSICAL
METHODS
 Hand weeding
 Hoeing
 Summer deep ploughing
 Mowing and slashing
 Chiseling
 Digging
 Chaining and dredging
 Soil solarization
 Flooding
 Burning
 Mulching

13. AGRONOMICAL/CULTURAL/ECOLOGICAL
METHODS
• Competitive crop and crop’s cultivars
• Time, method and seed rate
• Spacing
• Crop rotation
• Inter cropping and mixed cropping
• Time and method of irrigation
• Crop stimulation
• Stale seedbed
• Resistant crops and crop’s cultivars for parasitic weeds
• Summer fallowing
• Green manuring

14. CHEMICAL METHODS
In chemical weed control the herbicides are used for killi
ng the
herbaceous plants (weeds) growing in association with c
rop
plants.
HERBICIDES :- Herbicides are the chemicals capable of
killing or inhibiting the growth of plants.
 These chemicals vary greatly in their (a) molecular
structures, (b) mobility within plants, (c) selectivity, (d) fate
in soils, and (e) response to environment.
 Proper selection of the herbicide, its rate, time, and
method of application are very important to obtain the
desire degree of weed control and crop selectivity.

15. HERBICID
E WEED
CONTROL

16. BENEFITS OF HERBICIDAL WEED
CONTROL
• Herbicides allow the control of weeds where cultivation is difficul
t,
for example within and between narrowly spaced crops.
• Herbicides substantially reduce labour requirement
• Herbicides offer the efficient control of weeds
• Herbicides reduce the number of tillage operations needed for cr
op
establishment
• It permits early/timely planting in multiple cropping
• Special weeds (parasitic, perennial etc.) can only be controlled b
y
herbicides
• Herbicides allow flexibility in the management system
• Economical, particularly where labour is expensive
• Mechanical damage can be reduced
• Prevent depletion of soil moisture and nutrients

17. LIMITATIONS
1. INJURY TO THE CROP
2. RESIDUES IN THE CROP
3. RESIDUES IN SOIL
4. AIR, WATER, SOIL POLLUTION
5. IRRESPONSIBILITY IN DISPOSAL OF USED PESTICIDE
CONTAINERS SOMETIMES LEADS TO POISONINGS OF ANIMALS &
MAN
6. RESISTANT WEEDS
7. HAZARDOUS EFFECT ON FLORA AND FAUNA
8. COSTLY
9. IF CONCENTRATION OF CHEMICAL BECOME MORE THAN
RECOMMENDED THAN CROP BECOME UNFIT FOR CONSUMPTION

18. CLASSIFICATION OF
HERBICIDES
 i) Soil applied herbicides:
Herbicide act through root
and other underground
parts of weeds.
 Eg. Fluchloralin
 ii) Foliage applied
herbicides:
 Herbicide primarily active
on the plant foliage
Eg.Glyphosate, Paraquat
 i) Selective herbicide: A
herbicide is considered as
selective when in a mixed
growth of plant species, it
kills some species without
injuring the others.
 Eg. Atrazine
 ii) Non-selective
herbicide: It destroys
majority of treated
vegetation. Eg. Paraquat
1) Based on Method of
application
2) Based on Mode of action

19. > CONTINUE
 i) Contact herbicide: A
contact herbicide kills those
plant parts with which it
comes in direct contact Eg.
Paraquat
 ii) Translocated
herbicide: Herbicide which
tends to move from treated
part to untreated areas
through xylem / phloem
depending on the nature of
I) Inorganic
compounds
 II) Organic
compounds
3) Based on mobility 4) Based on molecular structure

20. 5) Based on Time of
application
1)Pre - plant application (PPI):- Application of herbicides before the crop is planted
or sown. Soil application as well as foliar application is done here. For example,
fluchloralin can be applied to soil and incorporated before sowing rainfed groundnut
while glyphosate can be applied on the foliage of perennial weeds like Cyperus
rotundus before planting of any crop
.
2) Pre – emergence application:- Application of herbicides before a crop or weed
has emerged. In case of annual crops application is done after the sowing of the
crop but before the emergence of weeds and this is referred as pre-emergence to
the crop while in the case perennial crops it can be said as pre-emergence to weeds
Eg. Atrazine, Pendimethalin

21. >CONTINUE
3) Post – emergence application:- Herbicide application after the emergence of crop
or weed is referred as post emergence application. When the weeds grow before the
crop plants have emerged through the soil and are killed with a herbicide then it is
called as early postemergence. Eg. Glyphosate, Paraquat, 2,4-D Na Salt.
4) Early post emergence:- Another application of herbicide in the slow growing crops
like potato, sugarcane, 2-3 week after sowing is classified as early post emergence.

22. FORMULATIONS OF
HERBICIDES
Herbicides in their natural state may be solid, liquid, volatile, non-volatile,
soluble or insoluble. Hence these have to be made in forms suitable and
safe for their field use & is prepared by the manufacturer by blending the
active ingredient with substances like solvents, stickers etc.
Objectives in herbicide formulations are
Ease of handling
High controlled activity on the target plants
Need for preparing herbicide formulation
To have a product with physical properties suitable for use in a
variety of types of application equipment and conditions.
To prepare a product which is effective and economically
feasible to use
To prepare a product which is suitable for storage under local

23. TYPES OF FORMULATIONS
I. Emulsifiable concentrates (EC): A concentrated herbicide
formulation containing organic solvent and adjuvants to facilitate
emulsification with water eg., Butachlor.
II. Wettable powders (WP): A herbicide is absorbed by an inert carrier
together with an added surface acting agent. The material is finely ground
so that it may form a suspension when agitated with a required volume of
water eg., Atrazine.
III. Granules (G): The inert material (carrier) is given a granular shape and
the herbicide (active ingredient) is mixed with sand, clay etc finely ground
plant parts (ground corn cobs) as carrier material. eg. Alachlor granules.
IV. Water soluble concentrates (WSC): eg. paraquat .
METHODS OF APPLICATION:-
1. Spraying
2. Broadcasting

24. SOME IMP. HERBICIDES OF SOME
RABI CROPS
CROP HERBICIDE DOSE
KG ai/kg
TRADE NAME &
FORMULATION
TIME OF
APPLICATION
1) WHEAT ISOPROTURON
2,4 D
0.60
0.4-0.6
• ARELON 75%
WP
•WEEDMAR
•PRE
EMERGENCE
•POST-
EMERGENCE
2) CHICKPEA
LENTIL
FIELD
PEAS
FLUCHLORALIN
PENDIMETHALI
N
0.70
0.75-1
• BASALIN 45% EC
• STOMP 30% EC
•PRE-
EMERGENCE
•PRE-
EMERGENCE
3)
RAPESEED
MUSTARD
BUTACHLOR
PENDIMETHALI
N
ISOPROTURON
1-1.5
0.75-1
0.75-1
• MACHETE 50%
EC
• STOMP 30% EC
• ARELON 75% WP
•PRE-
EMERGENCE
•PRE-
EMERGENCE
•PRE-
EMERGENCE

25. MODE OF ACTION OF
HERBICIDES
The term mode of action (MOA) 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 Blazer or Paraquat need to be applied post emergence to leaf tissue in
order to be effective. Seedling growth inhibitors, such as Treflan & Lasso, need to
be applied to the soil to effectively control newly germinated seedlings.
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.
RESISTANCE:- HERBICIDE RESISTANCE is the inherited ability of a plant to
survive and reproduce following exposures to a dose of herbicide normally
lethal to the wild type due to continuously usage of same chemicals over years.
In a plant, resistance may be naturally induced by such techniques as genetic
engg or selection of variants produced by tissue culture or mutagenesis.
SOME HERBICIDE RESISTANT CROPS
• WILD OAT ------- Avena fatua
•COMMON LAMBSQUARTERS --------- Chenopodium album etc

26. Integrated weed management (FAO,1966)
Integrated weed management (FAO, 1966) (IWM) :-- IWM means integrating
multiple methods to manage weeds, using the combination of practices that is
most effective for solving the specific weed issue at hand.
BENEFITS :--
 It long runs since combination of different methods.
 Provide longer and continuous control of weeds.
 Eliminate the chance of occurrence of weed flora shift,
herbicide-resistant in weeds, preponderance of perennial wee
ds.
 It is eco-friendly.
 It is complementary to IPM through continuous control of weed
s.