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Crop Protection 25 (2006) 487–495

www.elsevier.com/locate/cropro

Weed management in dry-seeded rice (Oryza sativa) cultivated in thefurrow-irrigated raised-bed planting system

Samar Singha, Lav Bhushanb, J.K. Ladhab,�, R.K. Guptaa, A.N. Raob, B. Sivaprasadb

aRice-Wheat Consortium for the Indo-Gangetic Plains, CIMMYT India, CG Block, NASC Complex, DPS Marg, New Delhi 110012, IndiabInternational Rice Research Institute (IRRI), IRRI-India Office, 1st Floor, CG Block, National Agriculture Science Center (NASC) Complex,

DPS Marg, Pusa, New Delhi 110 012, India

Received 10 June 2005; accepted 3 August 2005

Abstract

Dry seeding of rice (Oryza sativa L.) in the furrow-irrigated raised-bed planting system (FIRBS) represents a major shift in the

production practices for attaining optimal water productivity in the rice–wheat system in the Indo-Gangetic Plains of South Asia.

Information on weed management in dry-seeded rice in the FIRBS is lacking. Two experiments were conducted for 2 years, with an

objective of identifying appropriate, effective, and economical methods of managing: (1) broadleaf weeds only; and (2) a mixed

population of both grass and broadleaf weeds in dry-seeded rice cultivated in the FIRBS. The major weeds associated with dry-seeded

rice in the FIRBS during both years were Echinochloa crus-galli (L.) P. Beauv., Echinochloa colona (L.) Link, Dactyloctenium aegyptium

(L.) Willd., Leptochloa panicea (Retz.) Ohwl, Caesulia axillaris Roxb., Euphorbia hirta L., Lindernia sp., Commelina benghalensis L.,

Eclipta prostrata (L.) L., Trianthema portulacastrum L., and Portulaca oleracea L. Triclopyr at 500 g a.i. ha�1, bensulfuron at 60 g

a.i. ha–1, ethoxysulfuron at 18 g a.i. ha–1, and 2,4-D (ester) at 500 g a.i. ha–1, all applied at 21 days after seeding (DAS), were equally

effective in realizing higher rice grain yields by controlling broadleaf weeds. Among these, ethoxysulfuron at 18 g a.i. ha–1 was found to be

least expensive but effective for controlling broadleaf weeds. Effective and economical herbicides identified for managing a mixed

population of both grass and broadleaf weeds included fenoxaprop-p-ethyl+ethoxysulfuron at 50+18 g a.i ha–1, applied at 21 DAS, and

pendimethalin followed by (fb) chlorimuron+metsulfuron at 1000 fb 4 g a.i. ha�1 applied at 3 fb 21 DAS.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Rice-herbicides; Dry-seeded rice; Furrow-irrigated raised-bed system (FIRBS); Weed control; Costs

1. Introduction

The rice–wheat system, occupying 24 million hectares ofthe productive area in South Asia and China, is importantfor food security (Ladha et al., 2003). In recent years, themajor emphasis in the rice–wheat system has been onalternative resource-conserving technologies (RCTs) forboth rice and wheat to reduce the cost of cultivation andenergy consumption, to sustain productivity, and toincrease the profit margin of farmers. The RCTs underinvestigation are zero tillage, the furrow-irrigated raised-bed planting system (FIRBS), and rotary tillage (Chauhanet al., 2000). Dry seeding with subsequent aerobic soil

e front matter r 2005 Elsevier Ltd. All rights reserved.

opro.2005.08.004

ing author. Tel.: +9111 25843802; fax: +91 11 25841801.

ess: j.k.ladha@cgiar.org (J.K. Ladha).

conditions on raised beds avoids water required duringland preparation and thus reduces overall water demand(Bouman and Tuong, 2001). Drill dry seeding of rice in theFIRBS is more efficient in irrigation water use thantransplanted rice on puddle soil (Balasubramanian et al.,2003). Borrell et al. (1997) compared flooded rice with ricein the raised-bed system and found that the latter savedwater by 16–43%. The FIRBS saves on fertilizer nitrogen,seed and water and is being promoted in water-scarce areas(Sharma and Singh, 2002; Sharma et al., 2002).Weed infestation continues to be a serious problem in

dry-seeded rice. Aerobic soil conditions and dry-tillagepractices, besides alternate wetting and drying conditions,are conducive for germination and growth of highlycompetitive weeds, which cause grain yield losses of50–91% (Elliot et al., 1984; Fujisaka et al., 1993). Recently,

ARTICLE IN PRESSS. Singh et al. / Crop Protection 25 (2006) 487–495488

Singh et al. (2005) reported good success with dry-seededrice production technology in large-scale farmer participa-tory trials in the Terai of Uttaranchal, India, when thestale-seed bed technique was combined with the applicationof pre-emergence herbicide, pendimethalin within 2 daysafter seeding (DAS). Thus, timely weed control is crucial toincreasing rice productivity. Herbicides are considered tobe an alternative/supplement to hand weeding. Thedevelopment of new, improved herbicides for dry-seededrice is also needed (Gupta et al., 2003). Several pre-emergence herbicides including butachlor, thiobencarb,pendimethalin, oxadiazon, oxyfluorfen, and nitrofen aloneor supplemented with hand weeding, have been reportedto provide a fair degree of weed control (Estorninosand Moody, 1988; Castin and Moody, 1985; Janiya andMoody, 1988; Moorthy and Manna, 1993; Pellerin andWebster, 2004). But, some difficulties are associated withpre-emergence herbicides, such as their limited applicationduration (0–5 DAS) and requirement of adequate soilmoisture at the time of their application. In such situations,post-emergence herbicides are superior. Hence, it isnecessary to evaluate different pre- and post-emergenceherbicides that are formulated from time to time to providewider options to farmers for weed control in rice.

The FIRBS represents a major shift in productionpractices in the rice–wheat system. Weed control in rice isone area that still needs attention for effectively usingRCTs (Malik et al., 2003). To successfully grow rice onraised beds in northern Australia, Borrell et al. (1997) andSingh et al. (2005) concluded that additional herbicide, andtherefore cost, may be required to adequately controlweeds in a delayed-flood or unflooded system. Informationon weed management in dry-seeded rice using the FIRBS islacking. Farmers adopting the FIRBS for cultivation ofrice as an alternative to the conventional method will needweed efficient management methods to help reduceassociated weed competition risk. Surveys in farmers’ fieldsgrowing rice in the FIRBS in the Indo-Gangetic Plainsrevealed both grass and broadleaf weeds in other fields.Thus, it is essential to identify economic and effectiveherbicides and herbicide combinations for managing weedsin dry-seeded rice in the FIRBS. Hence, two studies wereconducted. One was aimed at identifying appropriatemethods of managing broadleaf weeds alone; the otherwas aimed at managing a mixed population of both grassand broadleaf weeds in dry-seeded rice in the FIRBS,effectively and economically.

2. Materials and methods

Two field experiments were conducted for two years(2003 and 2004) at the experimental farm of the SardarVallab Bhai Patel University of Agriculture and Technol-ogy, Modipuram, Meerut, Uttar Pradesh, India (29140Nand 771460E), at an elevation of 237m above mean sealevel. The climate of Modipuram is broadly classified assemi-arid subtropical, characterized by very hot summers

and cold winters. The hottest months are May and June,when the maximum temperature reaches 45–46 1C,whereas, during December and January, the coldestmonths of the year, the minimum temperature often goesbelow 5 1C. The average annual rainfall is 863mm, 75–80%of which is received through the northwest monsoonduring July–September. The experimental soil is silty loamin texture. The particle density of the soil is 2.65Mgm�3.The mean weight diameter of soil aggregates is 0.71mm,indicating a poorly developed soil structure, mainlybecause the soil reclaimed recently was alkali (sodic) innature. Soil (0–15 cm) retained 18% and 7% moisture(mass basis) at 30 and 1500 kPa suction, with plant-available water capacity of 11%. The soil reaction wasalkaline, with very low salt content. The surface soil(0–15 cm) has 0.83% total carbon, 0.09% total N,25mgkg�1 Olsen’s P, and 0.314meq 100 g�1 1N NH4OAC-extractable K. The DTPA-extractable Zn, Cu, Fe, andMn were in the high range in the surface soil layer.The experimental herbicide treatments included the

following: bensulfuron, cyhalofop butyl, 2,4-D (ester),ethoxysulfuron, pendimethalin, pretilachlor+safener, pro-panil, triclopyr, and almix (chlorimuron+metsulfuron).Specific details of each of the experiments follow.

2.1. Experiment 1. Evaluation of different herbicides for

controlling broadleaf weeds in dry-seeded rice in the FIRBS

A randomized complete block design (RCBD) with threereplications was used. The plots were 4.0m long with fourbeds (2.7m) in width. Eight treatments were included. Thetreatments are listed in Table 1. All the herbicides wereapplied at 21 DAS. Herbicides were applied using aknapsack sprayer with a flat fan nozzle and water ascarrier at 400 l ha�1. The grass weeds in the experimentalplots were controlled by pre-emergence application ofpendimethalin at 1.0 kg ha�1 at 3 DAS. Broadleaf weeddensity and dry weight data were collected at 30 and 60DAS. The grass weeds that emerged were removedmanually. Six hand weedings were done to maintain aweed-free situation in the weed-free treatment.

2.2. Experiment 2. Identifying effective herbicides for

managing a mixed population of grass and broadleaf

weeds in dry-seeded rice in the FIRBS

A RCBD with three replications was used. The plotswere 4.0m long with four beds (2.7m) in width. Eighttreatments were included. The treatments are listed inTable 5. Weed density and weed dry weight data werecollected at 45 and 75 DAS. One hand weeding was done inall treatments at 45 DAS. Six hand weedings were done tomaintain a weed-free situation in the weed-free treatment.For both experiments, rice (cv. NDR 359, a medium-

long duration variety) was planted in June and harvested inOctober in each year. Land preparation with a tractorconsisted of four ploughings (two times with a disc harrow

ARTICLE IN PRESS

Table 1

Density (no.m�2) and dry weight (gm�2) of broad leaf weeds in dry-seeded rice in the FIRBS as affected by different weed control treatmentsa,b

Treatmentc 30 DAS 60 DAS

Density Dry weight Density Dry weight

No.m�2 % Control gm�2 % Control No.m�2 % Control gm�2 % Control

Weedy 89 a 18.8 a 110 a 71.5 a

Weed-free 0 f 100 0 e 100 0 f 100 0 e 100

Triclopyr (500) 21 DAS 13 d 85.4 2.7 c 85.6 34 c 69.1 21.4 b 70.1

Triclopyr (1000) 21 DAS 6 e 93.3 1.0 d 94.7 23 d 79.1 17.1 c 76.1

Triclopyr (1500) 21 DAS 1 f 98.9 0.6 d 96.8 9 e 91.8 4.7 d 93.4

Bensulfuron (60) 21 DAS 38 b 57.3 8.4 b 55.3 21 b 80.9 19.9 b 72.2

Ethoxysulfuron (18) 21 DAS 26 c 70.8 5.4 c 71.3 12 c 89.1 6 d 91.6

2,4-D (ester) (500) 21 DAS 13 d 85.4 0.8 d 95.7 25 d 77.3 18.9 c 73.6

aIn a column, means followed by a common letter are not significantly different at the 5% level by DMRT.bData are average of two years (2003 and 2004).cDAS ¼ days after seeding, herbicide rate in g a.i. ha–1 indicated in parentheses.

Table 2

Density (no.m�2) and percentage control in density of broadleaf weeds as affected by different weed control treatments in dry-seeded rice in the FIRBSa

Wed species Density (D) and % control (% C)

Weedy Weed free Triclopyr (500)b Triclopyr (1000)c Triclopyr (1500)d Bensulfurone Ethoxysulfuronf 2,4-D (Ester)g

D D % C D % C D % C D % C D % C D % C D % C

C. axillaris 26 0 100 4 85 2 92 0 100 12 54 5 81 4 85

E. prostrata 15 0 100 1 93 0 100 0 100 5 67 1 93 0 100

E. hirta 10 0 100 1 90 0 100 0 100 6 40 5 50 0 100

T. portulacastrum 8 0 100 0 100 0 100 0 100 4 50 3 63 1 88

Lindernia spp. 10 0 100 1 90 1 90 1 90 1 90 0 100 1 90

P. oleracea 7 0 100 0 100 0 100 0 100 3 57 2 71 1 86

C. benghalensis 8 0 100 3 63 0 100 0 100 3 63 4 50 2 75

Other broadleaf weeds 6 0 100 2 67 1 83 0 100 3 50 4 33 2 67

Total 89 0 100 13 85 5 94 1 99 38 57 25 72 13 85

aData are average of two years (2003 and 2004).bTriclopyr (500) 21 DAS.cTriclopyr (1000) 21 DAS.dTriclopyr (1500) 21 DAS.eBensulfuron (60) 21 DAS.fEthoxysulfuron (18) 21 DAS.g2,4-D (ester) (500) 21 DAS ( DAS ¼ days after seeding, herbicide rate in g a.i. ha–1 indicated in parentheses).

S. Singh et al. / Crop Protection 25 (2006) 487–495 489

and two times with a cultivator) and one planking. Afterpreparation of the field, beds 37 cm wide with a furrow of30 cm were formed with the help of a tractor-drawn bedplanter. The rice was direct dry-seeded at 30 kg ha�1 in tworows per bed at 25-cm spacing using a tractor-drawn bedplanter. After seeding, irrigation was applied up to the toplevel of the beds and then subsequent irrigations wereapplied to make the soil saturated up to 1 month. Later,irrigation was applied at an interval of 4–5 days when therewas no rain. The N was applied at 150 kg ha�1 in threesplits, 1/3 each as basal, 42DAS, and 65DAS. Phosphorusat 60 kg P2O5 ha

�1 was applied with the bed planter duringseeding. Potash at 60 kg K2Oha�1 and zinc at 25 kg ha�1

ZnSO4 were broadcast in all plots uniformly before ricesowing.

Weed count, for estimating weed density, was recordedwith the help of a quadrant (0.5� 0.7m) placed randomlyat two spots in each plot. To record weed dry weight, weedswere cut at ground level, washed with tap water, sun dried,dried at 70 1C for 48 h, and then weighed. The data ofactual number of weeds were transformed by angulartransformation for statistical analyses. Grain yield wastaken from a 6-m2 area in the center of each plot andexpressed in Mgha�1 at 14% moisture.The statistical analysis of the data was done using

IRRISTAT Windows Version 4.1. The combined analysisof two years revealed that the year effect was notsignificant. Hence, mean data of two years were analyzed.Unless indicated otherwise, differences were consideredsignificant at pp0:05.

ARTICLE IN PRESS

Table 3

Grain yield and yield parameters of dry-seeded rice in the FIRBS as affected by different weed control treatmentsa,b

Treatmentc Grain yield (Mgha�1) Straw yield (Mgha�1) Panicles (m�2) Panicle length (cm) Grains (panicle�1)

Weedy 1.81d 3.06 c 128.3 b 21.18 c 75 c

Weed-free 5.21 a 7.80 a 216.8 a 24.37 a 129 a

Triclopyr (500) 21 DAS 4.47 b 7.07 ab 205.5 a 23.62 ab 113 a

Triclopyr (1000) 21 DAS 4.20 b 6.23 b 198.5 a 23.33 ab 113 a

Triclopyr (1500) 21 DAS 3.56 c 6.12 b 183.8 a 20.51 c 100 b

Bensulfuron (60) 21 DAS 4.63 b 6.44 b 194.5 a 22.98 ab 113 a

Ethoxysulfuron (18) 21 DAS 4.93ab 6.71 b 215.8 a 23.80 a 113 a

2,4-D (ester) (500) 21 DAS 4.46 b 6.46 b 206.7 a 22.63 b 113 a

aIn a column, means followed by a common letter are not significantly different at the 5% level by DMRT.bData are average of two years (2003 and 2004).cAs in Table 1.

Table 4

Cost and return analysis of different weed control treatments used for

managing broadleaf weeds in dry-seeded rice in the FIRBSa,b

Treatmentc Total costd

(US$)

Gross income

(US$)

Net income

(US$)

Weedy 397 218 �179

Weed-free 526 609 83

Triclopyr (500) 21 DAS NCAa 537 NCA

Triclopyr (1000) 21 DAS NCA 504 NCA

Triclopyr (1500) 21 DAS NCA 427 NCA

Bensulfuron (60) 21 DAS NCA 556 NCA

Ethoxysulfuron (18) 21 DAS 434 592 158

2,4- D (ester) (500) 21 DAS 428 550 122

aNCA ¼ not commercially available.bData are average of two years (2003 and 2004).cAs in Table 1.d1 US$ ¼ Rs. 45, hand weeding ¼ US$1.29 personday�1, ethoxysulfur-

on ¼ US$11.10 ha–1, 2,4-D ¼ US$4.66ha–1.

S. Singh et al. / Crop Protection 25 (2006) 487–495490

3. Results and discussion

3.1. Experiment 1. Evaluation of different herbicides for

controlling broadleaf weeds in dry-seeded rice in the FIRBS

The major broadleaf weeds associated with the dry-seeded rice in the FIRBS of this experiment were Caesulia

axillaris Roxb., Euphorbia hirta L., Lindernia sp., Comme-

lina benghalensis L., Eclipta prostrata (L.) L., Trianthema

portulacastrum L., and Portulaca oleracea L.All herbicide treatments resulted in lower weed density

and biomass than the weedy check. Triclopyr (1000 and1500 g a.i. ha–1) was superior to other herbicides inreducing weed density at 30 DAS (Table 1). 2,4-D (ester)was as effective as triclopyr in reducing weed dry weight atthat stage. Ethoxysulfuron and triclopyr (1500 g a.i. ha –1)were equally effective in reducing weed dry weight at 60DAS. Ethoxysulfuron was reported to be effective incontrolling a wide range of broadleaf weeds as well asperennial sedges, alone (Beaty et al., 1993; Hess and Rose,1995) or in combination with anilofos (Nagappa et al.,2002). The percentage control in density of individualweeds (mean of two years) as affected by different weedcontrol treatments at 30 DAS is given in Table 2. C.

axillaris was the predominant broadleaf weed in the weedycheck. Triclopyr (1500 g a.i. ha–1) achieved 100% control ofall major weeds in both years, except for Lindernia sp.,whose density was reduced by 90%. Triclopyr (1000 ga.i. ha –1) and ethoxysulfuron caused a 92% and 81%reduction in density of C. axillaris. The density of E.

prostrata was reduced by more than 93% by all studiedherbicides except bensulfuron which caused a 67% reduc-tion in density of E. prostrata. Bensulfuron was reported tobe effective on broadleaf weeds (Baldwin et al., 2001). Lowefficacy of bensulfuron in this experiment can be attributedto late application timing of bensulfuron tested in thisexperiment.

The yields of rice with all herbicide treatments werehigher than that of the weedy check (Table 3). Ethox-ysulfuron as a post-emergence treatment effectively keptbroadleaf weeds under control, resulting in grain yield

comparable with that of the weed-free treatment. Effectiveweed control and improved grain and straw yields withethoxysulfuron were earlier reported in transplanted rice(Bhowmick and Ghosh, 2002) and wet-seeded rice (Sainiand Angiras, 2002). Rice grain and straw yield with otherherbicide treatments did not differ from one another,except with triclopyr (1500 g a.i. ha–1). Triclopyr at 1500 ga.i. ha�1 was phytotoxic to rice and hence lesser yield wasrecorded, in spite of superiority in reducing weed densityand dry weight. Rice crop susceptibility has been animportant concern with triclopyr in the US (Scherder et al.,2000). Straw yield did not differ among herbicidetreatments. The yield data (Table 3) indicated thatphytotoxicity of triclopyr at 1500 g a.i. ha–1 resulted in asignificant reduction in panicle length and grains perpanicle of rice when compared with that of othertreatments. Based on these observations, it can beconcluded that triclopyr at 500 g a.i. ha�1, bensulfuron at60 g a.i. ha–1, ethoxysulfuron at 18 g a.i. ha–1, and 2,4-D(ester) at 500 g a.i. ha�1 were equally effective in achievinghigher grain yields by controlling broadleaf weeds in dry-seeded rice in the FIRBS.

ARTICLE IN PRESSTable

5

Density

(no.m�2)ofgrass

andbroadleafweedsin

dry-seeded

rice

intheFIR

BS,asaffectedbydifferentweedcontroltreatm

entsa,b

Treatm

entc

45DAS

75DAS

Grass

weeds

% Control

Broad

leaf

% Control

Total

% Control

Grass

weeds

% Control

Broad

leaf

% Control

Total

% Control

Weedy

104a

24a

128a

178a

43a

221a

Weed-free

0f

100

0e

100

0g

100

0h

100

0f

100

0e

100

Pendim

ethalinfb

chlorimuron+metsulfuron(1000fb

4)3fb

21DAS

19e

81.7

9cd

62.5

28f

78.1

23g

87.1

10d

76.7

33d

85.1

Pretilachlorwithsafener

fb

chlorimuron+metsulfuron(500fb

4)3fb

21DAS

35d

66.3

8cd

66.7

43e

66.4

29f

83.7

6e

86.0

35d

84.1

Cyhalofopbutylfb

triclopyr(120fb

500)14fb

28

DAS

50c

51.9

14b

41.7

64c

50

35e

80.3

16c

62.8

49c

77.8

Cyhalofopbutyl+

triclopyr(120+

500)14DAS

70b

32.7

13b

45.8

83b

35.2

53b

70.2

24b

44.2

79b

64.3

Propanilfb

triclopyr(1750fb

500)14fb

28DAS

60c

42.3

13b

45.8

73c

43

43d

75.8

20c

53.5

63bc

71.5

Propanil+

triclopyr(1750+

500)14DAS

51c

51

7d

70.8

58d

54.7

47c

73.6

20c

53.5

67bc

69.7

Fenoxaprop-p-ethyl+

ethoxysulfuron(50+

18)21

DAS

34d

67.3

10c

58.3

44e

65.6

23g

87.1

12d

72.1

35d

84.1

aIn

acolumn,meansfollowed

byacommonletter

are

notsignificantlydifferentatthe5%

level

byDMRT.

bData

are

averageoftw

oyears

(2003and2004).

cDAS¼

daysafter

seeding,fb¼

followed

by,herbiciderate

inga.i.ha–1indicatedin

parentheses.

Table

6

Dry

weight(gm�2)ofgrass

andbroadleafweedsin

dry-seeded

rice

intheFIR

BSasaffectedbydifferentweedcontroltreatm

entsa,b

Treatm

entc

45DAS

75DAS

Grass

% Control

Broad

leaf

% Control

Total

% Control

Grass

% Control

Broad

leaf

% Control

Total

% Control

Weedy

209.1

a9.8

a218.9

a416.8a

36.4a

453.2

a

Weed-Free

0g

100

0d

100

0g

100

0g

100

0f

100

0h

100

Pendim

ethalinfb

chlorimuron+metsulfuron(1000fb

4)3fb

21DAS

64.1

e69.3

3.6

b63.6

67.7

e69.1

63.8

e84.7

10.6

e70.8

74.4

f83.6

Pretilachlor+

safener

fbchlorimuron+metsulfuron

(500fb

4)3fb

21DAS

80.2

d61.6

1.7

c82.7

81.9

d62.6

86.3

d79.3

7.3

f79.9

93.6

e79.3

Cyhalofopbutylfb

triclopyr(120fb

500)14fb

28

DAS

67.9

e67.5

4.5

b54.1

72.4

e66.9

111.4

c73.3

15.6

d57.1

127d

72

Cyhalofopbutyl+

triclopyr(120+

500)14DAS

105.2

b49.7

3.9

b60.

109.1

b50.1

137.9

b66.9

21.6

b40.7

159.5

b64.8

Propanilfb

triclopyr(1750fb

500)14fb

28DAS

94.9

c54.6

4.9

b50

99.8

c54.4

110.3

c73.5

17.5

c51.9

127.8d

71.8

Propanil+

triclopyr(1750+

500)14DAS

93.5

c55.3

1.8

c81.6

95.3

c56.5

114.8

c72.5

20.5

b43.7

135.3c

70.1

Fenoxyprop-p-ethyl+

ethoxysulfuron(50+

18)21

DAS

56.8

f72.8

2.4

c75.5

59.2

f72.9

34.1

f91.8

11.6

e68.1

45.7

g89.9

aIn

acolumn,meansfollowed

byacommonletter

are

notsignificantlydifferentatthe5%

level

byDMRT.

bData

are

averageoftw

oyears

(2003and2004).

cAsin

Table

5.

S. Singh et al. / Crop Protection 25 (2006) 487–495 491

ARTICLE IN PRESSS. Singh et al. / Crop Protection 25 (2006) 487–495492

Economic analysis was done for the herbicides that arecurrently available to the farmers in the market (Table 4).Net returns were higher with ethoxysulfurn at 18 g a.i. ha–1.The next best was 2,4-D (ester) at 500 g a.i. ha�1, whichalso recorded higher net returns than the weed-freetreatment. 2,4-D can be applied only between tilleringand panicle initiation (Anonymous, 1997). In areas whererice is grown in proximity to cotton, triclopyr is used tominimize potential cotton injury (Beaty et al., 1993). Thisstudy thus reveals that ethoxysulfuron can be used foreffective and economical control of broadleaf weeds in dry-seeded rice in the FIRBS.

3.2. Experiment 2. Identifying effective herbicides for

managing a mixed population of grass and broadleaf weeds

in dry-seeded rice in the FIRBS

The major weeds associated with dry-seeded rice in theFIRBS during both years were Echinochloa crus-galli (L.)P. Beauv., Echinochloa colona (L.) Link, Dactyloctenium

aegyptium (L.) Willd, Leptochloa panicea (Retz.) Ohwlamong grasses; and C. axillaris, E. hirta, Lindernia sp., C.

benghalensis, E. prostrata, T. portulacastrum, and P.

oleracea among weeds.The density and biomass of grass and broadleaf weeds

with all the weed control treatments at all stages were lowerthan those of the weedy check (Tables 5 and 6). None of

Table 7

Density and percentage reduction in density of grass and broadleaf weeds at 30

in the FIRBSa

Weed species Density (D) and % control (% C)

Weedy

check

Weed

free

Pendi

fb AmxbPreti

fb Amxc

D D % C D % C D % C

E. crus-galli 47 0 100 7 85 13 72

E. colona 47 0 100 6 87 10 79

D. aegyptium 14 0 100 3 79 6 57

L. panicea 8 0 100 2 75 4 50

Other grasses 2 0 100 1 50 2 0

C. axillaries 8 0 100 2 75 1 88

E. prostrata 5 0 100 1 80 1 80

E. hirta 2 0 100 1 50 2 0

T. portulacastrum 2 0 100 2 0 1 50

Lindernia spp. 2 0 100 0 100 0 100

P. oleracea 1 0 100 0 100 0 100

C. benghalensis 2 0 100 1 50 0 100

Other broadleaf weeds 2 0 100 1 50 1 50

aData are average of two years (2003 and 2004).bPendimethalin fb chlorimuron+metsulfuron (1000 fb 4) 3 fb 21 DAS.cPretilachlor with safener fb chlorimuron+metsulfuron (500 fb 4) 3 fb 21 DdCyhalofop butyl fb triclopyr (120 fb 500) 14 fb 28 DAS.eCyhalofop butyl+triclopyr (120+500) 14 DAS.fPropanil fb triclopyr (1750 fb 500) 14 fb 28 DAS.gPropanil+triclopyr (1750+500) 14 DAS.hFenoxaprop-p-ethyl+ethoxysulfuron (50+18) 21 DAS (DAS ¼ days af

parentheses).

the herbicide treatments was as effective as the weed-freetreatment in reducing the density and biomass of weeds.Pendimethalin followed by (fb) chlorimuron+metsulfur-on, pretilachlor+safener fb chlorimuron+metsulfuronand fenoxaprop-p-ethyl+ethoxysulfuron were equally ef-fective in reducing total weed density at 75 DAS. Thedensity of both grass and broadleaf weeds was effectivelyreduced by these herbicide combinations. However, a lowertotal weed dry weight was observed with fenoxaprop-p-ethyl+ethoxysulfuron at 75 DAS. The next highestreduction in total weed dry weight was recorded withpendimethalin fb chlorimuron+metsulfuron and pretila-chlor+safener fb chlorimuron+metsulfuron at 75 DAS.Pendimethalin was reported to give the best grass weedcontrol (Estorninos and Moody, 1988; Joseph et al., 1990).When multiple weed problems exist, it becomes advanta-geous to use a mixture of herbicides to control bothbroadleaf and grass weeds (Brommer et al., 2000).Controlling broadleaf weeds and grasses is critical for

achieving maximum rice yields (Hill and Smith, 1990). Thedensity of individual weeds at 30 DAS (Table 7) revealedthat E. crus-galli, E. colona, D. aegyptium and L. panicea

were the predominant weeds. A greater reduction indensity of E. crus-galli occurred with pendimethalin fbchlorimuron+metsulfuron (85%) and pretilachlor+saf-ener fb chlorimuron+metsulfuron (72%) and the leastwith cyhalofop butyl+triclopyr (26%). E. colona density

days after seeding, with different weed control treatments in dry-seeded rice

Cyhal

fb TricdCyhal +

TricePropa

fb TricfPropa+

TricgFenoxa+

Ethoxyh

D % C D % C D % C D % C D % C

26 45 35 26 26 45 21 55 15 68

7 85 19 60 16 66 14 70 8 83

8 43 8 43 9 36 7 50 4 71

6 25 6 25 5 38 6 25 4 50

3 0 3 0 4 0 2 0 1 50

3 63 3 63 2 75 2 75 3 63

2 60 0 100 2 60 0 100 0 100

1 50 2 0 0 100 0 100 3 0

1 50 0 100 1 50 0 100 1 50

1 50 2 0 2 0 1 50 0 100

1 0 0 100 2 0 0 100 0 100

2 0 3 0 1 50 1 50 2 0

2 0 2 0 2 0 1 50 0 100

AS.

ter seeding, fb-followed by, herbicide rate in g a.i. ha–1 indicated in

ARTICLE IN PRESSS. Singh et al. / Crop Protection 25 (2006) 487–495 493

was reduced by more than 80% with pendimethalin fbchlorimuron+metsulfuron, cyhalofop butyl fb triclopyrand fenoxaprop-p-ethyl+ethoxysulfuron. Pendimethalinfb chlorimuron+metsulfuron (79%), fenoxaprop-p-ethy-l+ethoxysulfuron (71%) and pretilachlor+safener fbchlorimuron+metsulfuron (57%) were more effective inreducing density of D. aegyptium. All herbicides caused lessthan 50% reduction in the density of L. paniceae, except

Pendimethalin fb chlorimuron+metsulfuron, which caused75% reduction. Higher reduction in density of broadleafweed C. axillaris was obtained with pretilachlor+safenerfb chlorimuron+metsulfuron (88%), pendimethalin fbchlorimuron+metsulfuron (75%), propanil+triclopyr(75%) and propanil fb triclopyr (75%).

Rice yields with all herbicide combinations tested werehigher than that with the weedy check and lower than withthe weed-free treatment (Table 8). Yields with pendimetha-lin fb chlorimuron+metsulfuron, pretilachlor+safener fbchlorimuron+metsulfuron, fenoxaprop-p-ethyl+ethoxy-

Table 9

Cost and return analysis of different weed control treatments used for manag

Treatmentc

Weedy

Weed-free

Pendimethalin fb chlorimuron+metsulfuron (1000 fb 4) 3 fb 21 DAS

Pretilachlor with safener fb chlorimuron+metsulfuron (500 fb 4) 3 fb 21 DAS

Cyhalofop butyl fb triclopyr (120 fb 500) 14 fb 28 DAS

Cyhalofop butyl+triclopyr (120+500) 14 DAS

Propanil fb triclopyr (1750 fb 500) 14 fb 28 DAS

Propanil+triclopyr (1750+500 g) 14 DAS

Fenoxaprop-p-ethyl+ethoxysulfuron (50+18) 21 DAS

aNCA ¼ not commercially available in India.bData are average of two years (2003 and 2004).cAs in Table 5.d1 US$ ¼ Rs.45 (values adjusted to nearest US$), hand weeding ¼ U

on ¼ US$11.1 ha–1, fenoxaprop-p-ethyl ¼ US$16.67 ha–1, pendimethalin ¼ US

Table 8

Grain yield, straw yield, and yield parameters of dry-seeded rice in the FIRBS

and broadleaf weedsa,b

Treatmentc Grain yield

(Mgha�1)

St

(M

Weedy 1.24 e 2.3

Weed-free 5.23 a 6.3

Pendimethalin fb chlorimuron+metsulfuron (1000 fb 4)

3 fb 21 DAS

4.40 bc 5.7

Pretilachlor with safener fb chlorimuron+metsulfuron

(500 fb 4) 3 fb 21 DAS

4.27 bc 5.7

Cyhalofop butyl fb triclopyr (120 fb 500) 14 fb 28 DAS 3.78 cd 5.1

Cyhalofop butyl+triclopyr (120+500) 14 DAS 3.36 d 4.2

Propanil fb triclopyr (1750 fb 500) 14 fb 28 DAS 4.06 c 5.1

Propanil+triclopyr (1750+500) 14 DAS 4.37 bc 5.3

Fenoxaprop-p-ethyl+ethoxysulfuron (50+18) 21 DAS 4.66 b 5.7

aIn a column, means followed by a common letter are not significantly diffbData are average of two years (2003 and 2004).cAs in Table 5.

sulfuron, and propanil+triclopyr did not differ signifi-cantly. Increased yield through effective weed controlwas earlier reported with fenoxyprop ethyl (Lourenset al., 1989). The grain yield of dry-seeded rice in theFIRBS with weed-free treatment was more than in otherweed control treatments. Among herbicide treatments, thelowest grain and straw yields were observed with cyhalofopbutyl+triclopyr. This can be attributed to the phytotoxicityof triclopyr. Panicles number in the weedy check waslower. Rice 1000-grain weight with fenoxaprop-p-ethy-l+ethoxysulfuron and that of the weed-free treatment didnot differ.A cost and return analysis (Table 9) indicated the highest

net income with fenoxaprop-p-ethyl+ethoxysulfuron(50+18 g a.i. ha�1) applied at 21 DAS. The next highestnet return was with pendimethalin fb chlorimuron+met-sulfuron (1000 fb 4 g a.i. ha�1) applied at 3 fb 21 DAS.Both of them recorded higher net returns than the weed-free treatment.

ing grass and broadleaf weeds in dry-seeded rice in the FIRBSa,b

Total expenses

(US$)dGross income

(US$)

Net income

(US$)

397 149 �248

552 628 76

432 529 97

441 513 72

NCAa 403 NCA

NCA 403 NCA

NCA 487 NCA

NCA 525 NCA

444 559 115

S$1.29 day�1, chlorimuron+metsulfuron ¼ US$9.16ha–1, ethoxysulfur-

$6.67 ha–1, pretilachlor with safener ¼ US$15.56 ha–1.

as affected by different weed control treatments used for managing grass

raw yield

g ha�1)

Panicles

(m�2)

Panicle

length (cm)

Grains

(panicle�1)

1000-grain

weight g

5 e 131 c 20.5 c 86 b 25.1 b

1 a 271 a 23.6 a 107 a 27.4 a

3 b 244 ab 22.9 a 107 a 26.0 b

1 b 220 b 21.6 bc 102 ab 25.5 b

0 c 234 b 21.9 b 99 ab 25.8 b

4 d 230 b 21.8 bc 93 ab 25.8 b

9 c 241 ab 21.5 bc 102 ab 25.8 b

7 c 253 ab 21.8 bc 103 ab 25.7 b

1 b 237 b 22.3 a 99 ab 26.5 a

erent at the 5% level by DMRT.

ARTICLE IN PRESSS. Singh et al. / Crop Protection 25 (2006) 487–495494

A practice commonly used today is the application oftwo or more herbicides sequentially or in combination tobroaden the spectrum of weed control, reduce productioncosts, and/or prevent the development of weeds resistant tocertain herbicides (Bruff and Shaw, 1992; Zhang et al.,1995; Kelly and Coats, 1999). It can be concluded fromthese studies that effective control of both grass andbroadleaf weeds and higher grain yield and net returns ofdry-seeded rice in the FIRBS could be attained byapplication of either fenoxaprop-p-ethyl+ethoxysulfuron(50+18 g a.i. ha�1) at 21 DAS, fb one hand weeding at 45DAS or pendimethalin fb chlorimuron+metsulfuron (1000fb 4 g a.i. ha�1) applied at 3 fb 21 DAS fb one handweeding at 45 DAS. In fields where broadleaf weedspredominate, ethoxysulfuron alone could be used. Selec-tion of weed control measures based on the weed flora indry-seeded rice in the FIRBS would enable farmers tocontrol weeds with lower cost.

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