The document discusses chemical weed management methods in kharif crops. It begins by defining weeds and outlining their harmful effects on crop production. It then discusses various weed management techniques and focuses on the chemical method. It describes herbicide classification based on chemical nature, application method, timing, and mode of action. Common weeds in kharif crops are identified along with examples of herbicides used in rice, maize, soybean, sugarcane, cotton, and groundnut crops. Benefits and limitations of chemical weed control are provided. References for the information are cited at the end.

1. Chemical Approach For Weed Management In
Kharif Crops
(AGR001)
Submitted To- Dr. Shankar Lal Jat
Scientist (Agronomy)
ICAR- Indian Institute of Maize Research, Delhi
Submitted By- Rajni Godara
Roll No.- 11665 (Ph.D.)
Email- rajniiari1@gmail.com
Division of Agricultural Chemicals
ICAR- Indian Agricultural Research Institute, New Delhi

2. “Weed is an unwanted plant growing where it is not desired”
- Jethro Tull
• Weeds are undesirable or unwanted plants which interfere with
the utilization of land and water resources and thus adversely
affect human welfare
• The losses caused by weeds exceed the losses caused by any
other category of agricultural pests
Weed

3. Harmful Effects of Weed
• Nutrient loss
• Water loss
• Light penetration
• Space competition
• Insects and diseases
• Increased cost of production
• Low quality crop
• Allelopatheic effect
weed

4. Weed Management
It includes prevention, eradication and control by regulated use,
restricting invasion, suppression of growth, prevention of seed
production and by complete destruction

5. Methods of Weed Management

6. Chemical Methods
 The herbicides are used in chemical control of weeds
 Herbicides are chemicals used for killing weeds or inhibiting growth of weeds
 The first herbicide registered and used for selective control of weeds in crops was 2,4-
Dichlorophenoxy acetic acid (mainly for cereals against broad leaved weeds)
 Herbicide classification- The herbicides are classified on the basis of-
1. Chemical nature or composition
2. Method of application
3. Time of application
4. Mode of action
• Chemical nature or composition-
a) Inorganic Herbicides: Contain no carbon atoms in their molecules. These were the first chemicals
used for weed control before the introduction of the organic compounds, example- Acids: Arsenic
acid, arsenious acid etc; Salts: Borax, copper sulphate, ammonium sulphate etc.
b) Organic Herbicides: Oils and non oils contain carbon and hydrogen in their molecules e.g.
phenoxy acetic acid group, triazine group, Amides, Benzoics, Bipyridyliums, Carbamates,
substituted urea group, nitroanilines group etc.

7. • Method of application
a) Soil applied Herbicides: Herbicide act through root and other underground parts of
weeds e.g. Fluchloralin
b) Foliage applied Herbicides: Herbicide primarily active on the plant foliage e.g.
Glyphosate, Paraquat
• Time of application
a) Pre-Plant application: Application of herbicides before the crop is planted or sown.
Soil application as well as foliar application is done here e.g. fluchloralin
b) Pre-Emergence Herbicides: Apply herbicides prior to weed emergence at 1−3
DAS/DAT e.g. Simazine, Atrazine, butachlor, pretilachlor etc.
c) Post-Emergence Herbicides: Spray herbicides at 3−4 leaf stage of the weed. e. g
2,4-D , bentazon, Dicamba (Banvel) etc.
• Mode of action
a) Selective Herbicide: A herbicide is considered as selective when in a mixed growth
of plant species, it kills some species without injuring the others e.g. Atrazine
b) Non-selective Herbicide: It destroys majority of treated vegetation e.g. Paraquat

8. According to Herbicide Resistance Action Committee (HRAC)
classification of Herbicides on the basis of Mode of Action

9. Some Common Weeds in Kharif crops

10. Major Chemicals (Herbicides) Used in Various
Kharif Crops
1. Rice
Rice is generally cultivated as transplanted, wet-seeded and dry-seeded
▫ for transplanted rice - butachlor, pretilachlor
▫ for wet seeded rice - pretilachlor + fenclorim
▫ for dry seeded rice - oxadiazon, pendimethalin, oxadiargyl
• Some herbicides used in rice with dose and time of application data are given-
DAS- Day After Sowing; DAT- Day After Transplanting
Source- IRRI Rice Knowledge Bank
Herbicide Dose (kg a.i./ha) Time of application
2,4-D Na salt 0.8 21-28 DAT/DAS
2,4-D ester 0.9 5-7 DAT/DAS
Benthiocarb 2.0 2-3 DAT/DAS
Butachlor 1.25-2.0 2-4 DAT/DAS
Pendimethalin 0.75-2.0 3-5 DAT/DAS

11. 2. Maize
• It is grown in both rainy (June-October) and post-rainy (November-February)
seasons
• Some herbicides used in maize are as follow-
Source- Rana et al., 2016
Herbicide Dose (g/ha) Time of application Weeds controlled
Atrazine 0.75–1.0 Pre-emergence/ Early
post- emergence
Broad-spectrum weed
control. Some grasses are
tolerant
Alachlor 1.5–2.0 Pre-emergence Effective control of
grasses Suitable for
intercropping
Metolachlor 1.0–1.5 Pre-emergence Effective control of
grasses Suitable for
intercropping
2,4-D 0.50–0.75 Post-emergence Effective against broad-
leaved weeds
Paraquat 0.2–0.5 Post-emergence Broad spectrum weed
control

12. 3. Soybean
• Soybean being a rainy season crop suffers heavily due to weed competition and
losses due to weeds have been one of the major limiting factors in soybean
production
• Some herbicides used in soybean-
Source- Mishra et al., 2016
Herbicide Dose (g/ha) Time of application Weeds controlled
Fluchloralin 1000 Pre-plant incorporation annual grasses and some
broadleaved weeds
Trifluralin 1000–1500 Pre-plant incorporation annual grasses and some
broadleaved weeds
Pendimethalin 1000 Pre-emergence annual grasses and some
broadleaved weeds
Alachlor 1500 Pre-emergence annual grasses and some
broadleaved weeds and
sedges
Oxyfluorfen 150–200 Pre-emergence Controls wide range of
weeds including grasses,
sedges and broadleaved
Butachlor 1500 Pre-emergence annual grasses and some
broadleaved weeds and
sedges

13. 4. Sugarcane
• In India, sugarcane is planted in spring season (February-March), autumn season
(September-October)
• Being a long-duration crop (12–18 months), it is heavily infested with a variety of
weeds
• Some herbicides used in sugarcane are as follow-
Source- Rana et al., 2016
Herbicide Dose (kg/ha) Time of application
2, 4-D 0.75–1.0 Post-emergence
Simazine 1.5–2.0 Pre-emergence
Metribuzine 1.0 Pre-emergence
Diuron 2.5–3.0 Pre-emergence
Ametryn 2.0 Pre-emergence

14. 6. Groundnut
• It is a major oilseed crop of India and also an important agricultural export
commodity. In India, though groundnut is cultivated in one or more seasons (kharif,
rabi and summer) nearly 80% of the annual acreage and production comes
from kharif crop (June-October)
• Some herbicides used in groundnut-
Source- Mishra et al., 2016
Herbicide Dose (g /ha) Time of application Weeds controlled
Fluchloralin 1.0 Pre-plant incorporation annual grasses and some
broadleaved weeds
Alachlor 1500 Pre-emergence annual grasses and some
broadleaved weeds
Pendimethalin 1000 Pre-emergence For grasses and some
broadleaved weeds
Quizalofap-p-ethyl 50 Post-emergence grasses
Imazethapyr 75-100 Post-emergence broadleaved weeds

15. 5. Cotton
• Cotton is one of the most important fiber crops playing a key role in Indian economy. It faces very
stiff competition from weeds during the early stage of growth
• Some herbicides used in cotton-
Source- Mishra et al., 2016
Herbicide Dose (g/ha) Time of application Weeds controlled
Butachlor 1000–1250 3–4 DAS annual grasses and
some broad-leaved
weeds
Diuron 500–750 3–4 DAS broad-leaved weeds
Fluchloralin 1000 Pre-plant incorporation annual grasses and
some broad-leaved
weeds
Pendimethalin 1000–1500 3–4 DAS annual grasses and
some broad-leaved
weeds
Trifluralin 500–1000 Pre-plant incorporation annual grasses and
some broad-leaved
weeds

16. Benefits of chemical
method of control
• Herbicides can be applied for weed
control in crop rows and where
cultivation is impossible
• Pre-emergence herbicides provide
early season weed control
• Cultivation & manual methods of
weed control may injure the root
system
• Herbicides reduce the need for pre-
planting tillage. They are extremely
useful in minimalzero tillage
• Herbicides can control many perennial
weed which cannot be controlled by
other methods
Limitations of chemical
method of control
• The use of herbicides requires
technical knowledge regarding choice
of particular herbicide, time of
application safe dose method of
application etc.
• Over and under-dose of herbicides can
make a market difference between the
success or failure of weed control
• Certain herbicides because of their
long residual effect limit the choice of
next crop in the crop rotation
• Herbicides use may cause
environnemental pollution

17. Reference-
• Mishra, J. S., Rao, A. N., Singh, V. P., & Kumar, R. (2016). Weed
management in major field crops. Advances in Weed Management.
Indian Society of Agronomy, 1-23.
• Rana, S. S., & Krishi, C. H. P. Introduction to weeds, characteristics of
weeds, their harmful and beneficial effects on ecosystem.
• Rana, S. S., & Rana, M. C. (2016). Principles and practices of weed
management. Department of Agronomy, College of Agriculture, CSK
Himachal Pradesh Krishi Vishvavidyalaya, Palampur, 138.
• www.knowledgebank.irri.org

18. Thank you