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Integrated Weed Management in Rice in India
Adusumilli. N. Rao
Consultant Scientist, IRRI/India
Formerly Agronomist (Weed Scientist), International Rice Research Institute (IRRI),
Philippines;
Plot: 1294A; Road: 63A; Jubilee Hills; Hyderabad – 500033; Andhra Pradesh;
email: [email protected]
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1. Introduction:
Rice is cultivated in India in a very wide range of ecosystems from irrigated to shallow
lowlands, mid-deep lowlands, deep water to uplands.Transplanting is the major method of rice
cultivation in India. However, transplanting is becoming increasingly difficult due to shortage and
high cost of labour, scarcity of water, and reduced profit. Thus, direct-seeding is gaining
popularity among farmers of India as in other Asian countries. Direct-seeding constitutes both
wet- and dry-seeding and it does away with the need for seedlings, nursery preparation, uprooting
of seedlings and transplanting. Upland rice, which is mostly dry-seeded, is found in parts of Assam,
Bihar, Chattisgard; Gujarat, Jharkhand, Kerala, Karnataka, Madhya Pradesh, Orissa, Uttar Pradesh
and West Bengal. The upland rice area is around 5.5 million hectares which accounts or 12.33% of
the total rice area of the country. Wet-seeded rice (WSR) is increasing in area in parts of Andhra
Pradesh, Punjab and Haryana. In the rice agro-ecosystems ideal environment conditions are
provided for optimal rice productivity are being exploited by the associated weeds.
Irrespective of the method of rice establishment , weeds are a major impediment to rice
production through their ability to compete for resources and their impact on product quality.
Weeds are responsible for heavy rice yield losses, to the extent of complete crop loss under
extreeme conditions. . Out of the losses due to various biotic stresses, weeds are known to
account for nearly one third. Weed competition would be less severe under transplanting than
those under direct-seeding (Singh et al., 2005; Savary et al., 2005; Rao and Nagamani, 2007; Rao et
al., 2007). Uncontrolled weeds reduced the grain yield by 75.8, 70.6 and 62.6% under dry-seeded
rice (DSR), WSR and transplanted rice (TPR), respectively (Singh et al., 2005). Experiments showed
that yields were comparable across all establishment methods of rice when competition from
weeds was removed. Thus, weed control is major prerequisit for improved rice productivity and
production using different methods of rice establishment.
The agricultural growth rate has slowed down (2008-2009 reported less than 2%) in India
(Government of India, 2010) and increased agricultural productivity is needed to meet the
increasing needs of the growing population. Proper weed management technologies if adapted
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can result in an additional rice production. Thus weed management would continue to play a key
role to meet the growing food demands of increasing population in India. As the weed problems
are multi-pronged, a holistic multi-disciplinary integrated approach would be imperative. In this
context, integrated weed management (IWM) may provide a more sustainable approach to rice
production.
The objective of this paper is to provide a summary on integrated weed management in
rice in India and suggest areas of future research on integrated weed management to combat
weed menace effectively, economically and ecologically.
2. Impact/losses due to weeds
Weeds were reported to reduce rice yields by 12 to 98%, depending on type method of
rice establishment (Table: 1). Rice yield losses due to uncontrolled weed growth and weed
competition were least (12%) in transplanted rice (Singh et al., 2011) and highest in aerobic direct-
seeded rice on a furrow-irrigated raised-bed systems (Singh et al., 2008) and in dry-seeded rice
sown without tillage (Singh et al., 2011).
Threshold levels for a few weed species were also worked out. For example: Cyperus iria at
density of 30 m–2
and Echinochloa crus-galli density of 20 m–2
, is considered the threshold level for
transplanted rice, as it causes the minimum loss of 6.57% and 8.74%, respectively, in grain yield,
above which control measures are to be undertaken (Singh and Angiras, 2003; 2008). Grass weed
seedlings of rice seedling nursery are unintentionally transplanted with rice seedlings (Rao and
Moody, 1987) and average rice yield reductions from transplanted E. glabrescens ranged from 6%
at the 5% infestation level to 73% at the 40% infestation level (Rao and Moody, 1992).
An on-farm study indicated that the yield loss from weeds in unweeded plots was highest
in the rice-wheat system. followed by rice-pea-rice, and was least in the sugarcane system (Singh
et al., 2005). Weeds not only cause huge reductions in rice yields but also increase cost of
cultivation, reduce input efficiency, interfere with agricultural operations, impair quality, act as
alternate hosts for several insect pests, diseases, they affect aesthetic look of the ecosystem as
well as native biodiversity, affect human and cattle health.
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3. Weed flora associated with different methods of rice establishment:
Weeds are dynamic and the composition and competition by weeds is dependent on soil,
climate, cropping and management factors. Rice fields can be colonised by terestrial, semiaquatic
or aquatic plants depending on the type of rice culture and season. The total number of weeds
species in a field largely depends on the associated environment and cropping systems. It s usually
lower (10-15) in highly productive and intensive systems with a low diversity o crops grown in
rotation, and higher (upto 50 or more) under highly diversiied crop rotations. In either of the case,
only few of the species account or most of the damage (Moody, 1990). The number of species
comprising the major portion of the weed flora in any field is usually less than 10 and rarely more
than 3 or 4 species are important.
Several studies were conducted in India on weed flora of rice under different methods of
rice establishment and major associated weeds were reported (Table: 2). Echinochloa colona and
E. crus-galli are the most serious weeds affecting rice in all methods of rice establishment. Other
weeds of major concern in rice include, Ammannia baccifera, Cyperus iria, Cyperus difformis,
Eclipta alba, Fimbristylis miliacea, Ischaemum rugosum, Leptochloa chinensis, Monochoria
vaginalis, Paspalum distichum and Spaenoclea zeylanica. E. colona requires less moisture than E.
crus-galli resulting in the predominance of E. colona in dry-seeded rice. Cyperus rotundus and
Cynodon dactylon are other major problems in upland conditions, particularly in poorly managed
fields. Significant variation occurrs in the dominance of the abundant weed species with crop
establishment and weed control methods (Singh et al., 2005). Weedy rice is emerging as a major
problem in direct-seeded rice (Rao et al., 2007).
4. Factors influencing weed competition and critical period:
Many factors inluence the presence and abundance of weed species or groups of weeds in
rice fields. Important factors include: rice seeding method, soil moisture, crop rotation, type and
amount of ferilisers applied, time of ferilisers application, rice cultivar, water management; crop
management and weed control methods used. These factors inluence the weed growth and
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subsequently the rice productivity and quality. These factors are managed to provide optimal rice
stand and create microenvironment favorable for optimal rice productivity.
The critical period for weed control is a period in the crop growth cycle during which weeds
must be controlled to prevent yield losses (Zimdahl, 1988, 2004). Studies on critical period of crop
weed competition conducted in India (Table: 3) revealed that first thirty to seventy days are
critical, depending of the type of rice cultivar and the method of rice establishment.
The loss in grain yield of direct-seeded rice caused by unchecked weed growth was greater
when N fertilizer was applied and when the conventional practice of ploughing the fields just
before sowing was followed (Sharma, 1997). In transplanted rice, C. iria competition for the first
30 days caused less than one fourth (12.9%) of the total losses in yield while competition for 40
days resulted in more than half (43.5%) of the total losses due to the weed (Dhammu and Sandhu,
2002). Maximum reduction in rice yield (35.2%) was observed by delaying C. iria removal from 30
to 40 DAT, indicating this period as the most critical period of C. iria competition in transplanted
rice. On the otherhand, Singh et al., (1991) recorded over 25% of the total loss in rice yield when
Ischaemum rugosum was allowed to compete for 40 days and opined that the most critical period
of competition was 40-70 DAT. Thus, knowledge of weeds associated with rice and weed
emergence patterns becomes essential for successful implementation of critical period o crop
weed competition concept.
5. Principles of weed management
The principles that underline ecologicaly and economically viable weed management
system in rice are: (a) adapting the weed management options that suits to the environment of
the region, including soil, water, climate and biota present at the site; (b) optimizing the use of
biological and chemical/physical resources for effective management of weeds in rice. An
important principle underlying long-term weed management is that weed seed banks maintain
emergent populations, and therefore, seed banks must be managed at low densities to reduce the
potential for a buildup of intractably high weed populations.
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Reviews on weed management practices or rice nursery and transplanted rice (Rajendran
and Lourduraj, 1998); dry-seeded rice (Rao and Nagamani, 2007) and wet-seeded rice (Rajkumara
et al., 2003) in India are available.There is no single weed control method for effectively and
economically managing weeds in rice to attain optimal rice productivity and production. Hence,
integrated weed management strategy using a combination of several weed control methods is
often envisaged. The principles of IWM are that it must be : (i) effective, (ii) economical; (iii) easy
to use; (iv) and environmentally safe.
6. Integrated weed management
Weed management must aim at reducing the weed population to a level at which weeds
occurrence has no effect on farmers economic and ecological interests. By using different
appropriate management practices against weeds, farmers have more options for controlling
weeds, thereby reducing the possibility of escapes and weed adaptation to any single weed
management tactic. IWM is a science-based decision-making process that coordinates the use of
environmental information, weed biology and ecology, and all available technologies to control
weeds by the most economical means, while posing the least possible risk to people and the
environment (Sanyal, 2008). The concept of IWM is not new. For example, the traditional practice
of puddling soil to kill existing weeds and aid water retention, transplanting rice seedlings into
standing water to achieve an optimum stand density, and maintaining standing water to suppress
weeds, followed by one or several periods of manual weeding, is a well established example of
integrated weed management (IWM) (Rao et al., 2007).
Effective IWM combines preventive, cultural, mechanical and biological weed control
methods in an effective, economical and ecological manner.
6. A. Non chemical IWM:
Limited number of research studies were reported on non-chemical methods of IWM. In
rice seedling nursery rabbing (pre-burning the nursery area) gave 100% weed control (Zagade et
al., 1992). In transplanted rice, the reduction in weed growth was observed with, (a) intensive
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puddling and shallow depth submergence (Reddy and Reddy, 1999), (b) higher dosage rate of
fertilizer i.e.180 kg N ha–1
and plant density of 41 plants m–2
(Brar and Walia, 2001).
In rainfed upland rice, better land preparation (2 ploughings at 15 d before sowing and 2 at
sowing), timely sowing (in the last week of June), the application of fertilizer and an additional
hand weeding markedly decreases the infestation of all categories of weeds, compared to the
traditional farmers' practice, (Singh and Ghosh, 1992). In rice-rice cropping system, the least weed
growth was recorded with: (a) ploughing the land twice, during off-season followed by twice hand
weeding in the crop, (b) raising green manure of Sesbania aculeata (c) incorporation of pressmud
at 10 t ha–1
+Azolla inoculation at 1 t ha–1
(Gnanavel and Kathiresan, 2002). In rice/wheat cropping
system, inclusion of greengram in summer or summer cowpea for fodder or Sesbania for green
manuring, resulted in lowest grasses and sedges (Singh et al., 2008).
6. B. IWM with herbicides as a component:
In rice seedling nurseies, use of effective herbicides such as pretilachlor plus safener (Rao
and Moody, 1988; Balasubramanian, and Veerabadran, 1998); cyhaloop bytyl (Jayadeva et al.,
2002; Sharma et al, 2004a), propanil and quinclorac+bensulfuron (Rao and Moody, 1988) either
alone or in combination with hand weeding results in healthy rice seedlings for transplanting.
Several herbicides were found effective in managing weeds in different methods of rice
establishment (Table: 4, 5, 6). However, only about 17% area out of 42 mha under rice is treated
with herbicides, almost entirely in transplanted rice. Herbicides form only 12% of the pesticides
used on crops in India (Saksena, 2003; Bhat and Chopra, 2006). The rice herbicides such as
butachlor and anilofos have recorded huge increase in use upto 1650 and 500 MT, respectively. As
direct-seeded rice area is increasing in India, there exists a very good scope for their use in future.
Research on IWM was carried out to use herbicide as a component of weed management rather
than using herbicides alone.
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6. B. A. Crop rotations, cropping systems and herbicides:
Crop rotation is an important component of IWM. The choice and sequencing of crops
affects long-term weed population dynamics, and consequently weed management. In traditional
farming, rotations comprised of crops with different life cycles were a key component of weed
management. Different planting and harvest dates among these crops provide more opportunities
for farmers to prevent either plant establishment or seed production by weeds.
In rice/wheat cropping system, sequences involving summer cowpea for fodder or
Sesbania for green manuring, resulted in significantly lowest population of grasses and sedges
(Singh et al., 2008). However, the different cropping sequences failed to affect broadleaf weeds.
Rice-lentil+mustard (3: 1)-cowpea, rice-maize + pea (1: 1) - cowpea and rice –potato - greengram
gave high yield (Singh et al., 2008).
Effective weed control in terms of reduced weed density and dry weight was achieved by
pretilachlor with safener at 400 g ha–1
combined with sesbania (Daincha) intercropping and azolla
dual cropping in wet-seeded rice (Subramanian and Martin, 2006). The conoweeder incorporation
of daincha and azolla resulted in higher weed control during early stages.
In greengram intercropped with rice, pre-emergence application of pendimethalin 1.0 kg
ha–1
with hand weeding at 25 DAS significantly reduced the weed biomass and increased the yield
of both the crops (ICAR, 2007). In upland direct-seeded rice, an integrated strategy of growing
cowpea or dhaincha as an intercrop and pre-emergence application of pendimethalin (1.0 kg ha–1
)
followed by a manual weeding at 20 DAS has been found appropriate for reducing weed
competition (ICAR, 2007).
In rice-wheat system, sequential application of butachlor (rice) and isoproturon (wheat)
and butachlor fb hand weeding have been found effective against Echinochloa sp. and Fimbristylis
sp. in rice. Continuous use of butachlor in rice and isoproturon in wheat has reduced the problem
of Echinochloa colona in rice (ICAR, 2007). The effectiveness of crop rotation in weed suppression
may be enhanced by crop sequences that create varying patterns of resource competition,
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allelopathy, soil disturbance, and mechanical damage to certain weed species. Many aspects of
crop rotation and intercropping and their effects on weeds are yet to be explored.
6. B. B. Tillage and herbicides as components of IWM:
Tillage prior to crop establishment serves mainly to prepare a weed free seed bed. It
eliminates established and emerged prior to crop seeding and also moves weed seeds near the
soil surface vertically, resulting in weed seed burial. It is suggested that an integrated weed
management strategy involving summer ploughing, thiobencarb application and inter-crop
cultivation is essential for effective weed control in direct-sown, flood-prone, lowland rice, in
order to ensure higher N-use efficiency and crop productivity (Sharma, 1997).
In dry-seeded rice stale seedbed preparation was found better than traditional seedbed
preparation (Sharma et al., 2004). In transplanted rice: (a) frequent cultivations were better than
growing green manure or keeping field undisturbed after wheat harvest, (b) application of
pyrazosulfuron 0.015 kg ha–1
or two HW controlled L. chinensis and produced higher rice grain
yield rice (Aulakh and Mehra, 2006).
6. B. C. Integration of crop competitiveness with herbicides:
Farmers normally prefer high yielding varieties. Using high yielding crop variety
competitive against weeds in combination with other methods of weed control is one of the most
economical approach to attain optimal crop yield. Upland rice cultivars Vandana, Kalinga-III and
RR-151-3 have shown better weed competitive ability and higher yield potential under sub-
optimal weed management condition (ICAR, 2007). Rice cultivar ‘Gautam’ (high yielder) and
cultivar ‘Prabhat’ (better weed minimizer) + butachlor at 1.5 kg PE +2,4-D at 0.5 kg ha–1
POE
recorded highest rice yield with minimum weed dry weight (Singh et al., 2004).
Enhanced dry-seeded rice competitiveness against weeds was observed with 100 kg ha–1
seed rate + oxyfluorfen 0.25 kg ha–1
(3 DAS) + halod (Angiras and Sharma, 1998). The increase in
transplanted rice density from 22 to 44 hills m–2
+ application of pyrazosulfuron 0.015 kg ha–1
was
found to be significantly better in controlling L. chinensis (Aulakh and Mehra, 2006).
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6. B. D. Integration of herbicides with mulching:
Covering or mulching the soil surface can reduce weed problems by preventing weed seed
germination or by suppressing the growth of emerging seedlings. Mulches can be made from a
number of materials: a living plant ground cover, loose particles of organic or inorganic matter
spread over soil, and sheets of artificial or natural materials laid on the soil surface. Pre-
emergence application of pendimethalin at 1.0 kg ha–1
+ farm wastes as mulch (7.5 t ha–1
) + one
hand weeding at 45 days after sowing (DAS) of direct-seeded rice resulted in effective weed
control and higher crop yield (Singh et al., 2001).
6. B. E. Integration of zero tillage with herbicides:
The use of zero tillage would also reduce the costs of seeding. In rice-wheat system, under
zero tillage, the time taken between rice harvest and wheat sowing is considerably shortened and
early sowing of wheat after rice results in increased wheat yield (Vincent and Quirke, 2002).
Herbicide (pendimethalin at 1.0 kg ha–1
) as pre-emergence supplemented with two hand weedings
were needed to reduce weed growth in zero till dry-seeded rice (Singh et al., 2005a). In rained
lowland rice, Zero tillage and conventional tillage were similar in weed control efficacy when
supplemented with butachlor or hand weeding (Moorthy et al., 2002). In irrigated dry-seeded rice:
(a) zero tillage significantly reduced the total population and dry matter of weeds compared with
conventional tillage, but the difference in yield was not significant, (b) Integration of
pendimethalin 1.0 kg ha–1
or pretilachlor 0.75 kg ha–1
with 1 hand-weeding at 30 DAS or sequential
application of pre-emergence herbicides followed by post-emergence application of 2, 4-D (0.5 kg
ha–1
) and fenoxaprop (0.07 kg ha–1
), being on a par with each other, proved quite effective against
weeds (Mishra and Singh, 2008).
If weed seed production was minimized during the growing season, weed seedling
emergence in no-till would decline more across years compared with tilled systems as the surface
weed seed pool in no-till is depleted more rapidly by emergence and mortality. Burial of weed
seeds in soil by tillage favours persistence across time, thus leading to more weed seedlings in
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later years. Farmers can get additional benefits from this pattern of weed seedling emergence in
no-till systems when combined with crop diversity in their rotations.
6. B. F. Integration of hand weeding with herbicides:
Hand weeding is being practiced by farmers in India since they initiated agriculture. It is
effective on annual weeds. Hand weeding is ineffective against perennial weeds due to their
regenerative capability. Raising cost of labor and their non availability lead to the search for
alternative methods such as herbicide use either alone or in combination with hand weeding
(Singh et al., 2001; Rao and Nagamani, 2007; Rao et al., 2007). Several research publications have
proved that integration of herbicides with hand weeding is the most effective and economical
method of weed management (Table: 7).
7. Herbicide resistance and genetically modified rice
Continuous use of some herbicides has led to development of resistant weeds and has
exacerbated weed problems. For example, in rice–wheat cropping system of Punjab and Haryana,
Phalaris minor has developed resistance against isoproturon (Malik and Singh, 1995; Yaduraju and
Ahuja, 1995; Walia, and Brar. 2006). However, among weeds of rice, such resistance against
herbicides was not reported, yet, in India.
Incrasing concern o enviroment, toxicity to animals and persistence of residues in soil and
water lead to efforts to confer crops resistence against broadspectrum herbicides by applying
modern biotechnological techniques. The major direct benefits of introducing Herbicide-resistant
rice (HR-rice) are to: (1) improve control of weeds specifically associated with rice, such as weedy
Oryza species; (2) substitute currently used herbicides with new ones that are more efficient and
that have better environmental profiles; (3) provide new tools for managing weeds that have
already developed resistance to current herbicides and (4) facilitate adoption of resource
conservation technologies by improving weed management options. These benefits must be
weighed against risks beore the adoption o HR-rice in India. Malik et al. (2003) have suggested
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that herbicideresistant rice (HR-rice) would dramatically overcome weed problems in direct-
seeded zero till rice and reduce the need to puddle soils and keep them continuously submerged.
Three major HR systems currently commercialized are based on resistance to amino acid
biosysnthesis inhibiting herbicides viz. imidazolinone (IMI), glyphosate and glufosinate and in rice,
all three HR systems are being developed (Rao et al., 2007). Glufosinate-resistant and glyphosate-
resistant rice cultivars convey resistance to glufosinate and glyphosate, respectively, both of which
are broad-spectrum, nonselective, post-emergence herbicides with no soil or residual activity.
Both glufosinate and glyphosate-resistant rice are transgenic in nature. In contrast to IMI-rice,
development of glufosinate-resistant crops was accomplished through metabolic detoxification of
the herbicide. Information is limited on the developmentn of glyphosate-resistant rice. In India,
HR-rice is yet to be commercialised.
8. Future Research:
The research carried out on IWM in rice in India was mostly herbicide based. However,
majority of the farmers have not been benefited by herbicides in India. Herbicides must be made
economically and ecologically affordable to farmers by innovatively integrating with other
components of IWM. There is significant scope of growth in herbicides, as a component of IWM,
specifically as exports and domestic consumption of food grows. Need to step up coordinated
extension efforts to educate farmers on judicious use of herbicides in India, in integration with
other weed management methods.
Although herbicide-based systems have benefitted the agricultural community in many
ways, the heavy reliance on herbicides creates an environment favorable for weed resistance to
herbicides, weed population shifts, and off-site movement of herbicides. The current challenge for
producers is to manage herbicides and other inputs in a manner that prevents adapted species
from reaching troublesome proportions. Other major areas of future IWM research include:
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(a) On-farmassessment of losses caused by weeds: The yield losses caused by weeds in different
rice and rice based cropping systems in the farmers’ fields at different agro-ecological regions
need to be assessed.
(b) Understanding ecology of weeds associated with rice: Knowledge of intererence thresholds,
biology and growth habits of weeds of rice is essential to shift the crop weed balance in favor of
crop rather than weeds. For farmers to completely benefit from integrated weed management
technologies, mechanistic research must be conducted in weed ecology, genetics, and physiology
to increase basic understanding of the processes that regulate weed–crop interactions, weed
population dynamics, adaptation, and persistence under various management practices. IWM
should have a primary focus on practices that affect propagule production, survival, and the
propagule–seedling transition within the agro-ecosystem.
(c) Interdisciplinary effort: is needed to environmentally and economically viable components of
IWM practices in rice cropping systems. To tackle the complex weed problems, research must
involve, systems analysis, weed population and community analysis, weed traits eco-physiology,
molecular biology and genetics, assessment of pre- and post-control shifts in weed community,
herbicide resistance, issues related to transgenic plants, environmental issues, and potential
benefits of weeds.
(d) On-farm assessment of available IWM options: The IWM options identified by researchers
must be tested in the farmers’ fields to assess their effectiveness and economic viability. Despite
decades of research and extension efforts in popularizing the integrated weed management
(IWM) practices, its importance and effectiveness are not completely understood and hence less
adopted by the farmers. Closer linkage between research and extension is needed in evolving
IWM strategies and popularising effective and economical options to farming community.
(e) Exploiting the potentiality of biocontrol : Trichoderma viride and Gliocladium virens have been
found to control Phalaris minor in wheat and Echinochloa spp. in rice under laboratory conditions
without any adverse affect on the crop (ICAR, 2007). Role of biocontrol in IWM needs to be
exploited.
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(f) Developing knowledge based decision making tools: developing a larger database of weed
ecology and biology characteristics; developing, improving and refining integrated weed
management system simulation models; and determining the utility of these models as a
integrated weed management tool for growers and extension staff, as well as for predicting
further areas where research is required.
The challenge for weed scientists is to develop innovative, effective, economical, and
environmentally safe IWM systems that can be integrated into current and future cropping
systems to bring a more diverse and integrated approach to weed management in rice.
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Table: 1. Estimated yield losses caused by weeds in different methods of rice establishment in
India.
Method of rice
establishment
Weeds % reduction in yield due to weeds Reference
TPR Season long
competition
12 to 69.5% Rammohan et
al., 1999*;
Kathirvelan, and
Vaiyapuri,
2003*; Singh et
al., 2011*
Wet-seeded rice Season long
competition
85 Singh et al.,
2011*
Upland direct-
seeded rice
Season long
competition
93.6% Ladu, and Singh,
2006*
Dry-seeded rice-
zero tillage
Season long
competition
98 Singh et al.,
2011*
Dry-seeded rice pre-, post-flooding
periods
and complete crop
growth period
17.4 to 25.8; 10.03 to 48.3 and
34.4 to 72.6%
Moorthy and
Saha, 2001*
Upland rice Uncontrolled weeds 97.2% Singh et al.,
1988*
Rice-wheat In farmers fields 13.1 to 22.4 Singh et al.,
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cropping system 2005b*
Table: 2. Most reported weeds in different methods of rice establishment in India*.
Weed Name TPR WSR DSR
Echinochloa colona 1 2 1
Echinochloa crusgalli 2 3 6
Cyperus iria 3 1 3
Cyperus difformis 4 4 9
Fimbristylis miliacea 5 8 11
Eclipta alba 6 5 7
Cyperus rotundus 7 8 2
Ammannia baccifera 8 7 +
Ludwigia parviflora 9 6 +
Monochoria vaginalis 10 12 +
Cynodon dactylon 11 15 5
Commelina benghalensis 11 11 4
Marselia quadrifolia 12 10 +
Spaenoclea zeylanica 13 18 -
Paspalum distichum 14 20 +
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Panicum repens 15 16 +
Caesulia axillaris 15 + +
Leptochloa chinensis 16 17 -
Ischaemum rugosum 17 + 13
Digitaria sanguinalis 18 + 8
Phyllanthus niruri 19 + 6
Leersia hexandra 20 + -
Caesulia axillaris + 12 +
Fimbristylis dichotama + 19 -
Eluesine indica + + 10
Trianthema portulacastrum + + 12
Oriza sativa + + 20
Ageratum conyzoides + + 9
Cleome viscosa + + 13
Digera arvens + + 14
Dactyloctenium aegyptium + + 15
Celosia argentia + + 16
Aeschynomene indica + + 17
Setaria glauca + + 18
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Panicum dichotomiolia + + 19
Euphorbia heterophylla + + 20
TPR = Transplanted rice., WSR = Wet-seeded rice., DSR = Dry-seeded rice
1 = Most reported weed; 20= Less reported; + reported
* = Based on a survey of several published research papers in various journals
Table: 3. Critical period of crop weed competition (CPCWC) for rice under different methods of
rice establishment in India.
Method o rice establishment CPCWC* Reference
Transplanted rice (TPR) first 20 to 45 DAT Arokiaraj et al., 1989*;
Mukherjee et al., 2008*
TPR (between Caesulia axillaris
and TPR)
The initial period of 40–70 DAT Brar et al., 1995*
TPR between 4-6 weeks after
transplanting
Shetty and Gill, 1974*
TPR - Wrinkle Grass
(Ischaenllim rugosum Salisb.)
Between 50 and 70 DAT Singh et al., 1991*
Wet-seeded rice (WSR) 15 to 60 DAS Mukherjee et al., 2008*
Upland rice-direct-seeded rice first 30 DAS Tewari and Singh, 1991*; Ladu
and Singh, 2006*
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Upland bunded rice weed-free situation of 60 days
in monsoon and 70 days in
summer was found essential.
Mohamed Ali and Sankaran,
1984*
Drilled rice upto 45 days after sowing Gopal Naidu and Bhan, 1980*
Dry-seeded rice and Oxalis
latifolia
Upto 90 DAS Arya et al., 1991
* DAS = Days after seeding; DAT = Days after transplanting.
Table: 4. Herbicides reported to be effective in transplanted rice in India*
Herbicide Rate (kg ha–1
) Time of Application - Days
After Transplanting (DAT)
Acetachlor 0.10 to 0.150 3 DAT
Acetachlor+bensulfuron-methyl 0.250 5 DAT
Anilofos 0.4 3 -4 DAT
Anilofos fb HW 0.4 fb 1 HW 7 DAT
Anilfos+chlorimuron 0.300+0.008 3 DAT
Anilofos + [Chlorimuron ethyl +
metsulfuron mthyl ] (ready mix)
0.280 3 DAT
Anilofos+2,4-D 0.3 to 0.4 fb 0.5 Pre fb Post
Anilofos+2,4-DEE 0.875 5 DAT
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Anilofos+ethoxysulfuron 0.312 to 0.4 +0.012 to
0.015
10 DAT
Anilofos+ethoxysulfuron (ready
mix)
0.390 to 0.780 8 DAT
Anilofos+triclopyr 0.375+0.521 3 to 9 DAT
bentazon 1.5 10 DAT
Bentazone +2,4-D EE 1+0.5 6 DAT
Bensulfuron-methyl 50 and 60 g/ha 3 DAT
Bensulfuron-methyl 0.05 23 DAT
Bensulfuron-methyl+butachlor 0.050+0.938 5 DAT
Butachlor 1.5 to 2 3 to 5 DAT
Butachlor + [Chlorimuron ethyl +
metsulfuron mthyl]
1.0 to 1.25 +0.004 2 to 5 fb 20 to 25 DAT
Butachlor fb 2,4-D 0.5 to 1.5 fb 0.4 to 0.5 4 fb 25 DAT
Butachlor+ ethoxysulfuron 1.5+0.015 3 DAT
Butachlor fb propanil 1 to 1.5 fb 1 to 2 4 to 7 fb 21 to 30 DAT
Butachlor fb 1 HW 1.25 to 1.50 fb 1 HW 3 DAT fb 25 to 40 DAT
Cinmethalin 0.075 7 DAT
Cinosulfurom 0.010 10 DAT
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2,4-D 0.6 20-25 DAT
Clomazone+2,4-D EE 0.175+0.270 in Kharif
0.2+0.180 in Boro
3 DAT
[Chlorimuron ethyl +
metsulfuron mthyl ] +2,4-D EE
0.015+0.5 8 DAT
Clomazone+2,4D-EE (ready mix) 1 to 1.5 pproduct 3 DAT
Cyhalofop-butyl 0.18 7-8 DAT
Dicamba+2,4-D EE 0.5+0.8 21 DAT
Dinitramin 2 1 DBT
Fenoxaprop-p-ethyl 0.056 10 to 20 DAT
Fenoxaprop-
ethyl+ethoxysulfuron
0.060+0.015 15 DAT
Fentazamide 0.103-0.120 3-5DAT
Flufenacet 0.120 7 or 10 DAT
Fluroxypyr 0.4 10 DAT
Glyphosate (Zero tillage) fb
butachlor
1.25 fb 1.25 Before transplanting fb 7
DAT
Metsulfuron-methyl 0.010 20-25 DAT
Molinate granules 2 1 DBT
Naproanilide 1.5 10 DAT
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Oxadiargyl 0.07 to 0.1 3 to 5 DAT
Oxadiargyl + 1 HW 0.075+ 1 HW 4 DAT+40 DAT
Oxadiazon 0.75 to 1 2 to 4 DAT
Oxyfluorfen fb *Halod 0.25 fb One 3 DAT fb 20 DAT
Pendimethalin 1 to 1.5 3 to 4 DAT
Penoxsulam 0.0225 8 to 12 DAT
Piperofos 0.75 3 DAT
Piperophos/dimethametryn 1 6 DAT
Pyrazosulfuron-ethyl 0.020 3 DAT
Pretilachlor 0.4 to 1 3 DAT
Pretilachlor fb triasulfuron 0.009+0.045 3-5 DAT fb 12-15 DAT
Pretilachlor+2,4-D 0.3+0.3 3 DAT
Propanil 2 21 DAT
Pyrazosulfuron ethyl 0.015 to 0.25 3 to 10 DAT
Pyrazosulfuron methyl +
butachlor
0.025 + 0.939 3 DAT
Quinclorac 0.187 to 0.375 3 DAT
Thiobencarb 1.5 to 2.5 6 DAT
Thiobencarb +2,4-D 1 to 1.5 +0.5 5 to 6 DAT
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Triazolopyramidine sulfonamide 0.015 to 0.025 15 DAT
Tridiphane 0.48 10 DAT
Trisulfuron+pretilachlor 0.009+0.5 6 DAT
fb = followed by; * Summarised based on several published papers.
Table: 5. Herbicides reported to be effective in wet-seeded rice in India*
Herbicide Rate (kg ha–1
) Time of Application (DAS)
Anilofos 0.3 to 0.4 8 DAS
Anilofos 0.3 to 0.4 6 Days Before Seeding
Anilofos + ethoxysulfuron 0.312+0.012 Preemergence
Anilofos+2,4-D 0.30 + 0.40 10 DAS
Anilofos+ethoxysulfuron 0.312+0.012 10 DAS
Anilophos + 2,4-D EE fb 1 HW 0.30 + 0.40 fb 1 HW 6 DAS fb 25 DAS
Butachlor 1.0 to 1.5 6-8 DAS
Butachlor + pretilachlor 1.0 + 0.5 4-6 DAS
Butachlor + safener 1.0 to 1.5 1 to 5 DAS
Butachlor fb almix 1 fb 0.004 8 DAS fb 25 DAS
Butachlor+2,4-D 1.5+0.5 7 DAS
Butachlor+propanil 1.120+1.120 10-12 DAS
Butanil 1 8 DAS
Page | 31
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Chlorimuron+metsulfuron 4 g 15 to 20 DAS
Cyhalofop butyl 0.080 to 0.090 10 to 15 or 25 DAS
Cyhalofop-butyl fb butachlor+2,4-
DEE
0.075 fb 1.0+1.0
20 DAS fb 30 DAS
Cyhalofop-butyl fb2,4-DEE 0.090 fb. 1.0 20 DAS fb 30 DAS
Ethoxysulfuron 0.015 to 0.03 15 to 18 DAS
Fenoxaprop-ethyl +
ethoxysulfuron
0.060 + 0.015
15 DAS
Fenoxaprop-p- ethyl 0.015 20-35 DAS
glyphosate+pretilachlor+safener+2
HW
0.5 fb 0.4 fb 2 HW 20 DBS fb 3 DAS fb 25 and 45
DAS
Oxadiargyl 0.10 4 DAS
Oxyfluorfen 0.125 to 0.15 7 DAS
Pendimethalin 1 to 1.25 6 to 7 DAS
Pretilachlor 0.4 to 0.80 4 to 8 DAS
Pretilachlor + safener 0.4 3 to 8 DAS
Pyrazosulfuron 0.015 20-25 DAS
Thiobancarb 1.0 to 1.5 6 to 7 DAS
fb = Followed by; DAS = Days after seeding; * Summarised based on several published papers.
Page | 32
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Table: 6. Herbicides reported to be effective in dry-seeded rice in India*
Herbicide Rate (kg ha–1
)
Time of Application -
Days after seeding
(DAS)
Anilofos 0.4 7 DAS
Anilofos + 2,4-D 0.4+0.6 7 fb 25DAS
Anilophos fb Cyhalofop butyl 0.4 fb 0.09 3 DAS fb 35 DAS
Butachlor + safener 1.5 4 DAS
Butachlor fb 2,4-D 1.25 fb 0.5 PRE fb POST
Cyhalofop butyl 0.120 15 DAS
Dithiopyr 0.180 3 DAS
Fenoxaprop-p- ethyl 0.07 POE
Fluchloralin 1.5 PRE
Oxadiazon 0.5 PRE
Oxadiazon fb oxadiazon 0.4 b 0.4 PRE fb 45 DAS
Oxyflourfen 0.25 3 DAS
Pendimethalin 1.5 3 DAS
Pendimethalin fb 2,4-D 1 fb 0.6 PRE fb POST
Pretilachlor 1 2 DAS
Page | 33
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Pretilachlor+ safener 0.3 4 DAS
Pyrazosulfuron 0.015 to 0.030 6 DAS
Pyrazosulfuron ethyl + molinate 15 to 30 + 1.5 6 DAS b 15 DAS
Quinclorac 0.375 PRE
Thiobencarb fb 2,4-D 1 fb 0.5 PRE fb 20 DAS
Thiobencarb fb Cyhalofop butyl 1 fb 0.09 4 fb 35 DAS
PRE=Pre emergence application; POST = Post emergence; * Summarised based on several
published papers.
Table: 7. Most economical IWM methods for managing weeds in rice grown under
different methods of rice establishment in India.
Method of
rice
establishmen
t
IWM*
Reference
TPR (i) Application of butachlor 1.0 kg ha–1
,
anilofos 0.4 kg ha–1
along with closer planting
(ii) anilophos 0.6 kg ha–1
7 DAT + HW - 27 DAT
(i) Gogoi et al.,
2001
(ii) Singh and
Kumar, 1999
TPR rice+fish+poultry farming system+ oxyfluorfen at 0.25 Anbhazhagan
and Kathiresan,
Page | 34
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kg ha–1
2008
DSR butachlor @ 1.25 kg ha–1
as pre-plant surface
application+brown manuring+2,4-D @ 0.50 kg ha–1
at
40 DAS.
Maity and
Mukherjee, 2009
WSR the PSA of glyphosate at 1.6 kg ha–1
, PEA of butachlor
at 1.25 kg ha–1
fb one or 2 HW (at 35 and 55 DAS )
Sathyamoorthy
et al., 2004
WSR pre-sowing weed control (by conjunctive use of burn
down herbicide paraquat at 0.12 kg or tank mix of
glyphosate and 2,4-D Na salt at 0.20 kg + 0.20 kg a.i.
ha–1
, followed by subsequent weed submergence to
40 cm depth for 10 days) + sowing on clean seedbed
with preemergence herbicide (pretilachlor + safener
at 0.4 kg ha–1
) + post-emergence 2,4-D Na salt at 0.80
kg a.i. ha–1
Latif and
Wahab, 2007
DSR Mulching (pine needles (5 t ha–1
) or farm wastes (7.5 t
ha–1
)) + PE of pendimethalin at 1.0 kg ha–1
supplemented with one hand weeding at 45 days
after sowing or post-emergence application of 2,4-D
at 0.6 kg ha–1
Singh et al., 2001
DSR Stale seedbed preparation+pendimethalin+one
handweeding
Sharma et al.,
2004
DSR Stale seedbed preparation+criss-cross sowing
(CCS)+one handweeding
Sharma et al.,
2004
Rice - dry-Butachlor at 1.0 kg ha–1
f.b. one hand Singh and Singh,
Page | 35
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seeded rice weeding at 30 DAS by local tool 'Kutla' 2001
TPR/Wheat
cropping
system
Transplanting of rice after Sesbania aculeata (green
manure, GM) incorporation followed by conventional
tillage + Post-emergence application of sulfosulfuron
at 25 g ha–1
in wheat
Chitale et al.,
2007
* DAS = Days after seeding; DAT = Days after transplanting; DAP= Days after planting; HW=Hand
weeding; f.b. = followed by; PE = Pre emergence. DSR = Dry-seeded rice; TPR=Transplanted rice;
WSR= Wet-seeded rice.