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VIII. Weed Control Methods in Upland Rice

VIII. Weed Control Methods in Upland Rice

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314



S. SANKARAN AND S. K. DE DATTA



(Moody, 1975). Between 25 and 45 DAS each day of delay in weeding

reduced grain yield by 43 kg/ha and increased weeding by 23 labor-hr/ha (De

Datta, 1979). Three weedings produced the highest grain yield but required

530 to 838 labor-hr/ha. In terms of kilograms of rough rice per labor-hour,

one weeding at 25 DAS was most efficient.

Cultural practices such as land preparation, timely weeding (Moody,

1975), planting appropriate rices, using proper seeding rates, and fertilizer

management may partially substitute for chemical weed control in upland

rice.

Plant density and row spacing influence weed incidence. Bhan (1968)

found that narrow (15cm) spacing was superior to wide (30 and 45cm)

spacings in minimizing weed competition and increasing productive tillers

and yield in upland rice. However, Clarete and Mabbayad (1978) found that

15-, 30-, or 45-cm row spacings did not appreciably affect total weed count.

Reduced plant stand and wider row spacing left more area for weed growth

and caused low grain yields. Tosh et al. (1981) showed that row seeding

produced higher plant population, lower weed dry matter accumulation and

nutrient uptake by weeds, and higher grain yield than broadcast sowing

(Table XI). Merlier (1978) observed that maintaining optimum plant density

with a high seeding rate helped suppress vigorous weeds during early rice

growth.

Table XI

Effect of Seeding Methods on Weed Dry Matter Accumulation,

Nutrient Uptake, and Grain Yield'**



Seeding

method

Broadcast

Row

a



Plant

population

10 DAS

(No./m*)



Weed dry matter

accumulation

60 DAS

(gin2)



108 a

144 b



171 a

157 b



Nutrient uptake by weeds

60 DAS (kg/ha)

N



P



K



Grain

yield

(toniha)



10

9



2.7

2.4



28

22



1.5 a

1.8 b



Adapted from Tosh et al. (1981).

In a column, means followed by the same letter are not diifferent at the 5 % level by DMRT.



In Sierra Leone, Jones and Tucker (1978) tested rice straw and rice husk

mulches as weed suppressors and obtained 48 and 32% yield increases. Both

mulches controlled weeds as effectively as hand weeding. Results of IRRI

research showed very low soil moisture tension values (85 cbar and 1.75 bar)

in dry soil mulch plots and highest values (25-30 bar) in weedy fallow plots.

Dry soil mulch conserves moisture for the following upland rice crop. In



WEEDS AND WEED MANAGEMENT



315



weedy fallow plots, weed growth reduced the moisture available for the

following crop. Three tons of straw mulch per hectare and weed-free fallows

had intermediate soil moisture tension values. This information suggests the

benefits of dry soil mulch and straw mulch in weed control and moisture

conservation for upland rice (De Datta, 1981).



B. MECHANICAL

WEEDCONTROL

Different inter-row cultivators, hoe weeders, and rototillers are used to

control weeds in upland rice. Hoe weeding is fast, efficient, requires line

sowing (Curfs, 1975), and has many of the disadvantages of hand weeding.

Weeds can be hoed earlier than they can be pulled, but the weeding is more

thorough if within-row weeds are pulled by hand at the same time (Moody,

1975). Hoeing is superior to other mechanical weed control methods;

however, hoe and hand weeding are limited to small farms.

Hoeing alone often does not kill stoloniferous weeds and it may spread

them (Ivens, 1972). Intense rototilling during the dry season and growing

suitable dry season crops in rotation with rice can reduce weeds in upland

rice. In the Philippines, Rodriguez et al. (1982) found that intercultivation

with plow and hoe controlled weeds better than between-row hand weeding.

Most machines, whether hand pushed or attached to a two-wheel tractor,

performed poorly. Improved mechanical methods such as push-type and

motorized rotary weeders are not used in Africa (Akobundu and Fagade,

1978). In India, field experiments on rain-fed rice showed that hand hoe,

blade hoe, and rice weeders were as effective as hand weeding. They also

helped conserve soil moisture (Singh et al., 1976).

In Fiji, inter-row cultivation using horse-drawn implements successfully

controls weeds in widely spaced rows (Pate1 and Rhodes, 1969). In Ivory

Coast (Renaut, 1972) and Nigeria (IITA, 1973), inter-row cultivation to

control weeds has failed. Rice plants will be uprooted or severely damaged if

cultivation is too close to the rows. Therefore weeds within and close to the

rows, the most deleterious to yield, are not controlled. Renaut (1972) stated

that any weeding by inter-row cultivation would be virtually ineffective.

Work at IRRI using two inter-row cultivations with a hand hoe or highwheel cultivator followed by within-row hand weeding at 14 and 28 days after

emergence (DAE) produced yields equivalent to those from the weed-free

check, which was weeded 4 times (Singh et al., 1981). Hand weeding within

rows after inter-row cultivation increased yield an average of 0.5 ton/ha.

Inter-row cultivation followed by within-row hand weeding may substitute

for labor-intensive hand weeding.



316



S. SANKARAN AND S. K. DE DATTA



C. CHEMICAL

WEEDCONTROL

Pande and Bhan (1964) did not consider herbicides appropriate or

economical for weed control in upland rice, because of uncertain rainfall and

the low yield potential of upland cultivars. However, Velasco et al. (1961)

reported both chemical and mechanical weed control methods to be feasible.

Experiments at IRRI indicated that chemical weed control was economical

and effective (De Datta, l972,1974a,b). It may be the only method feasible for

large-scale rice production, considering the problems associated with other

weed control methods (Moody, 1975).

Chemical weed control in upland rice has been generally ineffective in

comparison with that in irrigated rice. Many of the available herbicides

(Table XII) are not sufficiently persistent in soil, are toxic to rice (Abifarin et

al., 1972), and are too expensive for small upland farms (USDA/USAID,

1968; Brown, 1969; Chabrolin, 1969).

(4-Chloro-o-toly1oxy)acetic acid (MCPA) and 2,4-D are widely used in

upland rice. Sanchez and Nurena (1970) reported that applying 2,4-D

satisfactorily controlled weeds in shifting cultivation areas with primarily

broadleaf species. With successive cropping, grasses became dominant

Table XI1

Herbicides Tested on Upland Rice of Asia, Africa, and Latin America"

Herbicide

Bifenox

Butralin

Dalapon

Dinitramine

Dymrone

Flurenol

Glyphosate

Isoproturon

Metobromuron

MSMA

Oryzalin

Paraquat

Pendimethalin

Piperophos

Piperophosdimethametryn



References

IITA (1974); Santos et al. (1977)

Mercado and Lubigan (1975); Deuse et al. (1978)

CIAT (1973); WARDA (1981)

Bhagat et al. (1977); Lopez and Mercado (1978); Moorthy and Dubey

(1981); Biswas and Thakur (1983)

Okafor (1973); Okafor and De Datta (1976a, b)

Tozani and Burga (1980)

CIAT (1973); WARDA (1981)

IITA (1974)

Ronoprawiro (1975)

CIAT (1973); Ronoprawiro (1975)

Uriarte and Garcia (1971); Mosha et al. (1977a,b)

Mukhopadhyay and Rooj (1971); Soerjani and Tirtarahardja (1971)

De Datta (1979); Pardo Del and Encina (1977); Pillai (1981); Moorthy

and Dubey (1981); Munroe et al. (1981)

Espinosa and Reyes (1976a,b)

IITA (1974); Jones and Tucker (1978); Moorthy and Dubey (1981)



a The list excludes 2,4-D, MCPA, butachlor, fluorodifen, nitrofen, thiobencarb, oxadiazon,

and propanil, which are discussed in detail in the text.



317



WEEDS AND WEED MANAGEMENT



(Moody, 1973) and 2,4-D was no longer effective. MCPA and 2,4-D have

been successfully used for upland rice weed control in India (Patro and Tosh,

1974), Philippines (Mercado, 1975), Indonesia (Soerjani and Tirtarahardja,

1971), Thailand (Teerawatsakul, 1981), Tanzania (Terry, 1976), Bolivia

(Tollervey et a/., 1980), Malagasy (Dobelman and Falais, 1968), Ghana

(Aryeetey, 1971), and El Salvador (Uriarte and Garcia, 1971).

Butachlor at 2 kg/ha was recommended for preemergence weed control

(De Datta, 1974a,b; Pillai et al., 1977; Okafor, 1979; Singh and Singh, 1983),

but it proved to be phytotoxic when applied soon after seeding (IITA, 1973;

Chandraka and Manna, 1981). However, in El Salvador, Gonzales (1972)

found that applying butachlor up to 3 kg/ha did not cause any phytotoxicity

in IR8, Santa Cruz, and Bluebonnet rices planted under upland conditions.

In West Africa, butachlor was not successful (Aryeetey, 1970; Renaut,

1972). Butachlor effectively controls several grass and broadleaf weeds at 2.0

to 2.5 kg a.i./ha. It has given excellent control of Calopogonium mucunoides

Desv., Melochia pyramidata L., and I. triloba in the Philippines (Tasic et al.,

1980) and Commelina erecta L., A . viridis, and E. indica in Brazil (Tozani et

al., 1976). Tasic et al. (1980) reported that applying preemergence butachlor

controlled weeds well and that rice yields were comparable with those of the

hand weeded (Table XIII). Similar results were obtained at IRRI (IRRI,

1974).

Table XI11

Effect of Weed Control Method on Weed Weight, Plant Height at

Maturity, and Grain Yield of Upland Rice C171-136'.b



Treatmentc

Complete weeding

(3 + 5 + 7 WAE)

Hand weeded twice

(3 + 5 WAE)

Butachlor

Butachlor fb hand weeding

(3 WAE)

Butachlor

No weeding



Herbicide rate

(kg/ha)



Weed weight

45 DASd

(kl3/ha)



Plant height

(cm)



Grain

yield

(to04



-



le



119 a



4.5 a



-



36 d



118 a



4.2 a



2.0

1.5



63 cd

74 c



119 a

118 a



4.1 ab

3.8 ab



115 a



3.5 b

2.6 c



1.5

-



133 b

158 a



105 b



Capiz settlement, 1979 wet season. Adapted From Tasic et at. (1980).

In a column, means followed by the same letter are not significantly different at the 5 % level

by DMRT.

' WAE, weeks after emergence; fb, followed by.

DAS, days after seeding.

a



'



318



S. SANKARAN AND S. K. DE DATTA



At 2.0 kg/ha, fluorodifen satisfactorily controlled upland weeds in Nigeria

(IITA, 1973), the Philippines (De Datta and Beachell, 1972; IRRI, 1974,

1979), Malagasy (Falais, 1978), El Salvador (Uriarte and Garcia, 1971), and

Tanzania (Terry, 1976). It performed poorly in Ghana (Aryeetey, 1970) and

New Guinea (Cates, 1969). In Colombia, preemergence fluorodifen was the

only selective herbicide in pregerminated rice (CIAT, 1973). Deuse et al.

(1978) reported that farmers in Senegal preferred fluorodifen at 3 kg a.i./ha

preemergence to hand weeding. Reports of the Senegal Institute (1973, 1975)

and Vuong et al. (1972) from Malagasy indicate that 4.0-4.5 kg fluorodifen

a.i./ha controlled most monocots.

Preemergence nitrofen controlled upland rice weeds at 2 to 4 kg a.i./ha in

India (Mukhophadyay et al., 1971, 1972; Bhan et al., 1972; Singh et al., 1979;

Dubey et al., 1980) and in Tanzania (Terry, 1976).

Oxadiazon performed well in several countries at 1 to 3 kg a.i./ha, as

demonstrated in studies by Tosh (1975), Bhagat et al. (1977), and Pillai (1981)

in India; Mercado and Razon (1978) and IRRI (1979) in the Philippines;

Falais (1978) in Malagasy; Smith (1973) in Panama; CIAT (1973) in

Colombia; and Uriarte and Garcia (1971) and Gonzales (1972) in El

Salvador.

Preemergence application of piperophos-dimethametryn at 2 kg a.i./ha

gave good control in Bangladesh (Ahmed and Islam, 1983), India (Bhagat et

al., 1977; Dubey et al., 1980), the Philippines (Mercado and Lubigan, 1975;

Mercado and Razon, 1978), and Sri Lanka (Gunasena and Kannangara,

1974).

Propanil is the most widely tested postemergence herbicide in upland rice.

A single application of 3 to 4 kg a.i./ha was as effective as repeated hand

weedings in three Asian, three African, and two Latin American countries.

However, propanil is a contact herbicide and several researchers (Aryeetey,

1970; Mayer and Chabrolin, 1972; Renaut, 1972) reported that a single

application was unsatisfactory. Sequential treatments at approximately 3week intervals on predominantly grass populations are probably better;

however, they may be cost prohibitive (Mayer and Chabrolin, 1972; Tosh,

1977).

Sequential application or application of a mixture of suitable herbicides

controls weeds best in upland rice. In Ghana, Carson (1975) reported that

1 kg a.i. propanil plus 2 kg a.i. thiobencarb/ha or 1.5 kg a.i. butachlor/ha

provided a more sustained and broader spectrum of weed control than one

herbicide alone. Propanil plus butachlor could be applied at various growth

stages with good results (Carson, 1977). Singh et al. (1977) harvested 3 tons

rice/ha with a presowing application of 0.5 kg a.i. butachlor/ha followed by

2.0 kg a.i. propanil/ha, as compared to 2 tons/ha in the hand weeded check.

Propanil mixed with either 2,4-D or MCPA gave excellent control in India



WEEDS AND WEED MANAGEMENT



319



(Chakraborty and Majumdar, 1973; Patro and Tosh, 1974), Bangladesh

(Gaffer, 1983), the Philippines (Vega et al., 1967; Mercado, 1975), North

Sumatra (Mangoensoekardjo and Kadnan, 1971a,b), Ivory Coast (IRAT,

1972; Renaut, 1972), Indonesia (Soetidjo and Sjarifullah, 1971), and El

Salvador (Gonzales, 1972).

In Panama, early postemergence application of propanil followed by 2,4,5T controlled weeds better than either propanil or 2,4,5-T applied alone. The

same combinations were efficient in Malagasy (Falais, 1978) and Colombia

(Morales and Vargas, 1976).

Other herbicides that can be mixed with propanil are thiobencarb (Morales and Vargas, 1976; Fagade, 1980), bentazon (Ghosh, 1976), fluorodifen

(Renaut, 1972; WARDA, 1973; Espinosa and Reyes, 1976a,b; Fagade, 1980),

dichlobenil (Renaut, 1972), alachlor (Renaut, 1972; Sharma et al., 1977),

oxadiazon (Smith, 1973), and swep (Takabayashi and Nakayama, 1973).

Preplant mixtures of S-ethyl dipropylthiocarbamate (EPTC) plus MCPA

and molinate plus 2,4-D as preplant and postemergence applications gave

satisfactory weed control in upland rice (Bhan et al., 1972). A combination of

swep, MCPA (Doming0 and Palis, 1966), and fluorodifen followed by 2,4-D

(IITA, 1972; Renaut, 1972); presowing MSMA followed by postemergence

2,4-D amine; and a presowing mixture of metobromuron and 2,4-D amine

(Mangoensoekardjo and Kadnan, 1970; Soerjani and Tirtarahardja, 1971)

satisfactorily controlled weeds in upland rice. Preemergence mixtures of

neburon (IRAT, 1972), prometryne with butachlor/oryzalin (Uriarte and

Garcia, 1971), oxadiazon with prometryne or oryzalin (Bullon, 1975), pendimethalin and fluazifop-butyl (Migo and De Datta, 1985), piperophos and 2,4D tank mixture (Biswas and Thakur, 1983),and terbutryn with 2,4-D (Vuong

et al., 1972) were moderately effective in upland rice.



D. WEEDCONTROL

IN UPLAND

RICE-BASED

CROPPINGSYSTEMS

Each crop has its characteristic weeds, and growing the same crop

continuously on the same land tends to increase them (Akobundu and

Fagade, 1978). Navarez et al. (1983) studied changes in weed population

caused by weed control practices in an upland rice-mungbean pattern at

IRRI. The R. exaltata population declined substantially after 2 years in plots

hand weeded thrice for rice and twice for mungbean. However, C. rotundus,

different grasses, and broadleaf weeds replaced R. exaltata. Continuous use of

two hand weedings in both crops caused fewer changes, and R. exaltata

remained dominant with one weeding.

Results of several field studies on weed control in upland rice show that a

presowing or preemergence herbicide application followed by one hand



320



S. SANKARAN AND S. K. DE DATTA



hoeing and weeding is more efficient and economical than conventional hand

weeding.

In India, applying 1 kg a.i. 2,4-D sodium salt/ha 1 week before sowing

followed by one hand hoeing 4 weeks after sowing gave the highest grain

yield and net return (Singh and Khan, 1972). Similar results were reported by

Misra and Roy (1970) with a presowing spray of 2,4-D and MCPA 6 days

before seeding followed by one hoeing and weeding. Results were superior to

those following the local practice of one harrowing and two manual

weedings. Mukhopadhyay and Bhattacharyay (1967) and Upadhyay and

Choudhary (1979) reported that hoeing and weeding for 3 weeks followed by

a 6-week postemergence spray of 2.5 kg a.i. propanil/ha effectively controlled

weeds and gave a high grain yield. Dixit and Singh (1981) obtained a yield

comparable to the yield from two hand weedings using propanil followed by

one hand weeding (Table XIV).

Table XIV

Effect of Weed Control Treatment in Upland Rice on

Grain Yield and Yield-Attributing Charactersa**



Productive

tillers per m2



Number of

grains per

panicle



Test weight

of 1000 grains



Treatment



Grain

yield

(tonha)



Control (nonweeded)

Propanil plus MCPA

Propanil plus one hand weeding

Hand weeded twice



1.5 a

3.9 b

4.2 b

4.3 b



213 a

275 b

301 c

311 c



64 a

81 ab

83 ab

85 b



20 a

21 a

21 a

21 a



~



(g)



___________



Adapted From Dixit and Singh (1981).

* In a column, means followed by the same letter are not significantly different at the 5 % level

by DMRT.



A preemergence application of 2 kg a.i. butachlor/ha followed by one hand

weeding 3 weeks after rice emerged provided excellent weed control in India

(Singh and Chauhan, 1978), the Philippines (Clarete and Mabbayad, 1978),

and Bangladesh (Ahmed and Islam, 1983), giving yields comparable to that

from the weed-free check. In the Philippines, Munroe et al. (1981) reported

that applying butachlor in combination with one hand weeding gave similar

grain yield to the weed-free check (Table XV) and reduced the required

frequency of weeding and labor dependence. In India, a postsowing application of trifluralin followed by hand weeding produced grain yields similar to

those of the hand weeded control (Bongolan et al., 1981). In Nigeria, Fagade

(1976) reported that a single application of 3 kg a.i. propanil/ha followed by

one hoe weeding 14 days later gave yields comparable to those with two hoe

weedings.



321



WEEDS AND WEED MANAGEMENT



Table XV

Effect of Weed Control Treatment on Rice Yield of Upland Rice at

Four Sites in the Philippines".*

Grain yield (ton/ha)

Treatment



Bauan



Cuenca



Tanauan



Santa Elena



Weed-free check

Butachlor 2.0 kg a.i./ha plus hand weeding

Weedy check



3.2 a

3.4 a

1.5 b



4.0 a

3.9 a

0.3 b



4.6 a

4.6 a

2.8 b



3.5 a

3.5 a

0.8 b



' Adapted From Munroe et al. (1981).



* In a column, means followed by the same letter are not significantly different at the 5 % level

by DMRT.

E. BIOLOGICAL

WEEDCONTROL

Several reports are available on successful weed control in cropped and

uncropped areas by insects, pathogens, snails, etc. However, there is little

published information on such weed control in upland rice.

A study of the weed-host range of the rice root nematode Hirschmanniella

spinicaudata Sch. Stek. 1944 conducted at Ibadan in Nigeria may be relevant

(Babatola, 1980). Of the 45 weed species tested, 33 were very susceptible,

including the broadleaf weeds Commelina diflusa Burm. f. and Murdannia

nudiflora (L.) Brenan, the grasses E. colona, C. dactylon, and R. exaltata, and

the sedges C. rotundus and C. diformis. A. conyzoides and A . sessilis were

moderately susceptible. These results suggest that H. spinicaudata may be a

potential biological agent for control of upland rice weeds.

Most biological agents have the disadvantage of controlling only one

weed. Nevertheless, biological control offers important potential for future

study and has advantages such as lack of harmful residues for crop and

environment.



F. INTEGRATED

WEEDCONTROL

Integration of several weeding methods has proven effective and is

suggested by various workers to be the best weed control system for upland

rice (De Datta, 1980; Lopez et al., 1980; Sabio and Pastores, 1981; Tosh et al.,

1981). Combining controls can reduce the buildup of perennial weeds caused

by continuous use of the same herbicide, weeding method, or cropping

system (De Datta, 1980).



322



S. SANKARAN AND S. K. DE DATTA



The first step in integrated weed control is to grow an upland rice cultivar

that is highly competitive with the weeds. However, Lopez et al. (1980) found

that changing rice varieties did not significantly affect the number and dry

weight of weeds or the labor required for hand weeding. Nevertheless,

improved rices outyielded the traditional rices. Varieties that emerge rapidly

have high seedling vigor. Those that rapidly develop a canopy compete most

successfully with weeds.

Noda (1977) developed a model (Fig. 9) that compares the advantages of

integrated weed control with those of individual controls. In rice, the

interdependence and interrelation of cultural and chemical methods were

emphasized by Smith and Shaw (1966). They suggested that integrated weed

control is effective, economical, and environmentally sound.

De Datta (1977b) observed that an efficient perennial weed management

system for rice should integrate preventive measures, crop rotation, soil and

water management, tillage practices, competitive varieties, and herbicides.

Kolhe and Mittra (1981) found that postemergence application of propanil

20 DAS followed by hoeing between rows 20 days later satisfactorily

controlled weeds in upland rice. Drilling rice seeds in rows followed by a

postemergence application of propanil in two splits also was effective (Tosh

et al., 1981). A preemergence spray of pendimethalin followed by postemergence propanil at 15 DAS and one hand weeding at 50 DAS in upland rice

controlled weeds as effectively as four hand weedings (Rodriguez, 1980).



v

Preventive means



\



Manual weeding



environmental^



Increasing yield



safety



Mechanical control



productivity

Chemical control



f



I 4 /\



Cultural methods

coexistin with

other teclniques



-1



Increasing

yield / lobor



Limits of weeds

without yield loss



weed science



useful agents



FIG.9. A conceptual model of integrated weed control. (Adapted from Noda, 1977.)



WEEDS A N D WEED MANAGEMENT



323



IX. YIELD RESPONSE OF RICE TO HERBICIDES

AND HERBICIDE COMBINATIONS

Many preemergence and postemergence herbicides and their combinations

have been tested in the upland rice areas of Asia, Africa, and Latin America.

Table XVI lists the herbicides that gave yields comparable to the hand

weeded check.

In Asia, butachlor appears to be the most efficient preemergence herbicide

for upland rice, either alone (De Datta, 1972; Clarete and Mabbayad, 1978;

Ahmed and Islam, 1983; Bongolan et al., 1981; Manipon et al., 1981),

followed by one hand weeding (Singh and Chauhan, 1978; Munroe et al.,

1981; Sabio and Pastores, 1981), or followed by propanil (Sharma et al.,

1977). Grain yield increased 2 ton/ha in several sites. The other promising

preemergence herbicides for high grain yields were thiobencarb (Bueno et al.,

1975), oxadiazon (Bhagat et al., 1977), and pendimethalin (Singlachar and

Chandrasekar, 1977; Moorthy and Dubey, 1981; Pillai, 1981; Sankaran and

De Datta, 1984).

Of the postemergence herbicides evaluated, propanil at 2.0 to 4.0 kg a.i./ha

(Kaushik and Mani, 1980; Kolhe and Mittra, 1981) was the most effective.

Split applications of propanil (Chakraborty, 1974; Tosh et al., 1981) and tank

mixtures with 2,4-D (Mangoensoekardjo and Kadnan, 1971b; Patro and

Tosh, 1974; Gaffer 1983) encouraged high upland rice yields.

In Africa, oxadiazon (WARDA, 198l), piperophos-dimethametryn (Jones

and Tucker, 1978), thiobencarb (Kennard, 1973), and fluorodifen (Fagade,

1980), either alone or in combination with postemergence propanil, were the

most successful preemergence herbicides (Carson, 1975; Fagade, 1980).

Applying propanil followed by one hand weeding (Fagade, 1976,1979) after

rice emerged gave better grain yields than conventional hand weeding.



X. PHYTOTOXICITY OF HERBICIDES AND RESIDUES

Mangoensoekardjo and Kadnan (1971a,b) found propanil to be toxic to

rice at 2.8 to 3.5 kg a.i./ha combined with 0.6 kg a.i. 2,4-D/ha. The symptom

generally was leaf burn. Leaf tips turned brown and dried, but usually only

about half the leaf dried. Younger leaves and those that emerged later were

normal, with normal growth resuming after about 2 weeks. Moorthy and

Dubey (1981) observed that oxadiazon at 1.0 kg a.i./ha could severely reduce



Table XVI

Effect of Single Herbicide and Herbicide Combinations on Upland Rice Yield versus Effect of Hand Weeded and Untreated Controls

Grain yield (tonha)

W



w

P



Efficient herbicide

(kg a.i./ha) and its

combination"



Efficient

herbicide/

combination

A



Asia

Alachlor (2.5)

Butachlor (2.0)

Butachlor (1.0)

Butachlor (2.0)

Butachlor (2.0) fb one HW

Piperophos-dimethametryn (2.0)

Linuron (1.0) fb one HW

Pendimethalin (2.0)

Pendimethalin (2.0) fb one HW

Penoxalin (2.0)



2.6

3.6

1.1

3.2

3.5

3.6

2.5

2.7

2.9

3.8



Hand

weeded

B



Untreated

control

C



Yield

increase

over control

(A - C)



Reference



3.5

3.6

1.6

2.6

3.5

3.2

1.9

3.3

2.9



0.8

1.o

0.4

0

0.8

0

0.2

0.6

1.0

1.6



1.8

2.6

0.7

3.2

2.7

3.6

2.3

2.1

1.o

2.2



Ghosh et al. (1977)

Ahmed and Islam (1983)

Cadag and Mercado (1980)

De Datta (1972)

Munroe et al. (1981)

De Datta (1979)

Sabio and Pastores (1981)

Pillai (1981)

Sankaran and De Datta (1984)

Moorthy and Dubey (1981)



4.0



Country



India

Bangladesh

Philippines

Philippines

Philippines

Philippines

Philippines

India

Philippines

India



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VIII. Weed Control Methods in Upland Rice

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