Livestock Research for Rural Development 11 (2) 1999

Citation of this paper

Use of local ducklings to control insect pests and weeds in the growing rice field

Bui Xuan Men, Tran Kim Tinh, T R Preston*, R Brian Ogle** and Jan Erik Lindberg**

Faculty of Animal Husbandry, Cantho University, Vietnam
*Finca Ecologica, University of Agriculture and Forestry, Ho Chi Minh City, Vietnam
**Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden


Abstract

An experiment was conducted on a smallholder farm in Omon district in the Mekong Delta to evaluate the ability and efficiency of local ducklings in controlling damages from insect pests and weeds in the growing high yielding rice field. The trial included 4 treatments allocated at random in 4 blocks, each of 33*210m, in a direct seeded rice area. The treatments were: (1) rice area managed with complete chemical (CtrP), (2) rice area fertilized with 50% of the nitrogen applied to CC plus ducks (DU-N/2), (3) rice area with only ducks without any chemicals (DU O), and (4) rice area without any chemicals or ducks (CtrN). The ducks were introduced into the growing rice plots at two weeks of age when the rice had been seeded for 22 days and removed at 52 days when the plants started flowering. A mash of broken rice and fish meal was supplemented to the ducks throughout the growth cycle.

The rice yields were 4,240, 3,888, 2,176, and 496 kg per hectare (P<0.05) for the CtrlP, DU-N/2, DU Oand CtrN treatments,  respectively. Duck mortality during the experiment was zero.  Weights at 63 days were 1,313 and 1,300 for the DUN/2 and DU treatments,  respectively. The net economic benefits were highest for the DUN/2 treatment.

Key words: Local ducks, growth, rice production, integrated pest management, weeds


Introduction

The duck industry has been developed in Vietnam over a long time and plays an important role in providing income for smallholders, and meat and eggs in the diets of the people. Ducks can be found throughout the country, but are concentrated in the Mekong Delta which has about 60% of the total. The farmers have various traditional systems for raising ducks, of which the rice-duck system is very common. In this system ducks forage in the growing rice fields and farmers can get more production from rice due to the fact that ducks control insects and weeds and excrete manure which fertilizes the rice plants, and decreases the need for chemicals.

Damage by insect pests is a serious problem for the young rice plants, especially the high yielding rice varieties commonly cultivated today (Kim 1984. So, the rice producers must make large investments in the purchase of various kinds of pesticides and insecticides, which also involves additional labour for spraying, particularly as several pesticides are required to kill pests at different periods of growth of the rice. Over-use of toxic chemicals in rice cultivation has resulted in pollution of the environment, especially damaging to the health of humans, fish and other aquatic and domestic animals when their residues are deposited in the soil and washed into the canals and waterways. By applying various biological control methods the farmers could limit the developments of pests and weeds in their fields.  The use of ducklings to control pests and weeds is one strategy already known by many producers in the Mekong Delta, although very little research has been done to evaluate the mechanisms involved.

Along with these benefits the producers can get more benefit from ducks raised in the harvest season, because they forage for natural feeds and left-over rice in the rice fields and decrease the need for investments in purchased feeds. Also, small flocks are commonly let loose in the backyards or gardens, and are fed household wastes or rice by-products, and obtain other feeds by scavenging. Additionally, duck production helps reduce unemployment in the rural areas and increases the incomes of the poor farmers, especially landless farmers.

In order to contribute to the knowledge and understanding of duck-rice integrated smallholder systems, a trial concerned with rearing ducks in the rice field was carried out on a small-holder farm to evaluate the ability and efficiency of ducklings in controlling insect pests and weeds in the growing rice field.

Methods and Materials

Experimental Design

There were 4 treatments allocated at random in 4 blocks of the rice area (33m x 210m) on a small-holding in Phuocthoi village, Omon district, Cantho Province.

The treatments were:

The treatments were separated (isolated) by clear plastic sheets tightly attached to bamboo frames 1 m high from the ground up and 0.3 m from the ground surface down (buried in the mud) and completely surrounding each plot, which minimized insects crossing over and chemicals dissolving and being moved by flowing water between treatments. The ducks in treatment DU-N/2 and DU O were driven onto the growing rice plots at two weeks of age with a density of 20 ducklings per 360m plot on direct seeded rice land 22 days after sowing the seeds. They scavenged on the plots until day 52 from seeding, when the plants started to flower, at which time the ducks were removed to prevent damage to the developing grains of rice. The ducks in treatments DUN/2 and DU  were allowed free access to the plot areas and scavenged all of the day and also at night. Apart from scavenging, a mash of broken rice plus fish meal (average of 76g/day per duck) was supplied to the ducks three times per day at 8:00, 12:00 and 18:00. They could drink water directly in the rice field or from water stored in drinkers taken from the ditch near the rice field. Between flowering and harvesting the rice plots controlled by the ducks received the same treatment (if any) as for all plots (sprayed with pesticides according to what the farmers normally do). During the growth stage of rice the farmer used agricultural chemicals to control pests and weeds and fertilized the rice plants as shown in Table 1.

Table 1: Chemicals used for rice as recommended and applied by the farmer

Chemical names (in brands)

Effect on

1

Pesticides
Trebon
Factas
Azodrine
Hailuaxanh
Bam
Validamycine
Fujone
Opus
Till
Anvill


Hoppers, worms
Leaf rolling worm
Stem worm
Hoppers, stem worm, leaf worm
Stem worm, hoppers
Fungi
Fungi
Fungi
Fungi
Fungi

2

Herbicides
Tiller's
2,4D


Weeds
Weeds

3

Fertilizers
Urea
DAP
K2O
KNO3
Bioted


Growth of rice plants
'
'
'"
''

The fertilizers used in the experiment had the following formulae and were applied as indicated in Table 2:

Table 2:  Fertilizers used in the integrated duck-rice experiment

Fertilizer

CC

DUN/2

DU

C

Urea, kg/ha
DAP, kg/ha
K2O, kg/ha
KNO3, kg/ha
Bioted, litres/ha

440
140
56
14
11

220
140
56
14
11

0
0
0
0
0

0
0
0
0
0

The components of the feed given to the ducks consisted of 72% broken rice, 10% fine rice bran (polishings), 17.75% dried fish meal and 0.25% premix vitamin/trace minerals. The composition of the feed was as follows: crude protein (N*6.25) 17%, estimated ME 3060 kcal/g, Ca 0.99%, and P 0.66%. After removal from the rice field the ducks were kept in a shelter and fed the same feed up to finishing at 9 weeks of age.

To test the capacity of the ducks to consume insects and weeds a counting frame (50*50*60cm) was placed at random at 4 sites on each of the rice plots once a week and all insects, weeds, snails were identified and counted. This was carried out one day before the ducks were driven into the rice field (3 weeks from seeding) and at 4, 5, 6, 7 and 9 weeks of age of the rice plants. The aims of the trial were to make comparisons of the treatment pairs as follows:

Parameters measured were: growth of rice, insect damage, weed problems, yield of rice, soil status; growth and survival rates of ducks, feed conversion rates of ducks, chemical composition of feeds, and costs and economic benefits from duck and rice farming.

Experimental site

The experiment was carried out on a farm representative of common conditions of Binh Khanh hamlet of Omon district of Cantho province, where the duck population is relatively dense and high yielding rice is cultivated. The cropping season during which the trial was carried out was the spring-summer period, i.e. from February to June, 1998.

Results and discussion

Efficiency of ducks in eliminating pests and weeds in the growing rice field.

By sampling and counting insect pests in the experimental rice plots it was found that 10 kinds of pests were mainly responsible for the damage to the rice plants. The pests that developed rapidly and caused major damage in order of importance were (translation of local name, with Latin names in brackets): small leaf-rolling worms (Snaphalocrosis medinalis), big leaf-rolling worms (Parnara guttata), float worms (Nymphula depunctalis), Keo worms (Spodotera litura), brown plant hopper (Nilapavata lugens), white backed plant hopper (Sogatella furcifera), green leaf hopper (Nephotettix cincticeps), dotted backed hopper (Recilia dorsalic), green measure worms (Naganra aenescens Moore), stem borers (Chilo suppressalis), Locusts (Locusta migratoria manilensis), and Bulach pests (Stenchaetothrips oryzae). Use of integrated duck-rice farming in the early growth stage of rice eliminated or decreased dramatically most of these pests from one or two weeks onwards. It can be seen in Table 3 that most of the worm species responsible for major damage in the early growing period tended to decrease two weeks after the introduction of ducks into the plots.

Table 3: Developments of some major insect pests in the growing rice plots controlled by ducklings

Parameters

Age of rice plant, week

Name of pests

treatment

3

4

5

6

7

9

Small leaf-rolling worm ** (Snaphalocrosis medinalis), unit/m

CC

7.2

9.6 a

0.2 a

0 a

0.8

18.8 a

DU+N/2

7.0

5.2

3.8 b

1.4

1.6

10 b

DU O

4.2

1.2 bc

1.2 a

0.2 a

0.6

3 c

CtrN

4.6

4.2 bc

2 ab

3 b

1.2

1 c

Float worm 
(Nymphula Depunctalis),
units/ m

CtrP

19.2

3.4 a

0

0 a

0

0

DU+N/2

14.8

0 a

0.4

0.8 a

0

0

DU O

12.9

0.6 a

0

0 a

0

0

CtrN

10.6

13.8 b

0.8

4 b

0.8

0

Green measure worm (Naganra aenescens),
units/m

CtrP

20.0

2.6 a

0

0 a

0.6

0

DU+N/2

12.6

0.2 a

0.4

0.6 a

1.2

0

DU O

19.4

0.4 a

0

0.4 a

0.2

0

CtrN

11.4

8.6 b

1.6

6.8 b

0.6

0.4

Total hoppers 
(brown, white, green),
units/m

CtrP

1906

4460 abd

575 a

245 abd

13.2 a

4.6

DU+N/2

1094

701 b

180 b

102 b

6

9.2

DU O

925

29 c

74 b

5.6 c

3.6 b

5.6

CtrN

1044

1353 db

43.4 b

399 db

8.2

5.8

abcd Different letters in each column of blocks are significantly different (P<0.01)
** Local name

There were a total of 9 kinds of weeds in the rice plots of the experiment. From Table 3 it can be seen that the common species of weeds responsible for inhibiting the growth of the young rice were to a large extent eliminated two weeks after the introduction of the ducks. The weeds developed rapidly and dominated the rice plants in the negative control plot. The rice plants remaining were very thin and weak, and there were very few grains per ear. The cause of the problem was that the rice plants couldn't grow well because they were too weak to compete for nutrients with the vigorous species of weeds as shown above. Another problem was that when the weeds become established, and are not eliminated, they continue producing seeds which spread widely and affect the following crop of rice. Integrating ducks and rice will result in continued decreasing investments for producers by also eliminating the weeds in the next crop because the ducks eat all parts of the weeds and grass seeds as shown by observations of the crop contents of scavenging ducks (Bui Xuan Men, unpublished  data).

Table 4: Mean values for weed populations in the different treatments

Parameters

Age of rice plant, week

Weed

Treatment

3

4

5

6

7

9

Chat weed*
(Fimbristylis miliacea),
u
nits/m

CtrP

127

2.6 a

0.6 a

0.4 a

0 a

0 a

DU+N/2

134

0.4 a

1.6 a

0.2 a

0.4 a

0 a

DU O

83.6

6.2 a

9.6 a

6.2 a

3.4 a

6 a

CtrN

106

161 b

359 b

261 b

217 b

254 b

Chao weed, 
(Cyperus difformis),
units/m

CtrP

48.0

22 b

2.8 b

5.6 b

2.2 b

0.8 a

DU+N/2

91.0

3.4 b

1.6 b

1.8 b

2 b

1.6 a

DU O

24.2

17.8 b

2.4 b

6.2 b

3.8 b

4.6 a

CtrN

122

187 a

336 a

279 a

108 a

365 b

Choc weed 
(Monochoria vaginalis),
units/m

CtrP

0

0.4

2 a

1.4 a

0.2 a

2 a

DU+N/2

0.8

0

0 a

0 a

0 a

0 a

DU O

0.4

0

0 a

0.2 a

0.2 a

0 a

CtrN

0

0.8

7.4 b

11.4 b

8.2 b

10.6 b

ab Columns in blocks with different letters are significantly different;  * Local name

From Table 4 it can be seen that weeds are a major problem in the high yielding rice fields. If they are not cleaned out by chemicals or by hand they will soon dominate the young rice plants. In this experiment the ducks were kept at all time in the rice plots so they had more opportunity to consume the different species of young weeds, and also to trample them so that they could not develop. Two kinds of weeds, Chat weed (Fimbristylis miliacea) and Chao weed (Cyperus difformis) were major problems when they appeared and grew alongside the young rice plants, because they usually grow faster and compete strongly for nutrients and water, and can reduce rice grain yields by up to 50% (Nyarko and Datta 1991). However, they were mostly eliminated 3 weeks after the ducks were introduced into the rice plots.

Yields of the experimental rice treatments
Table 5:   Mean values for yields of rice, income, variable costs and benefits

Treatment

Yields, kg/ha

Income, ha
VNDong

Variable cost/ha VNDong

Benefits/ha
VNDong

CtrP

4240

7630,000

4000,000

3630,000

DU+N/2

3888

6998,400

2945,000

4055,000

DU O

2176

3916,800

2610,000

1306,800

CtrN

  496

  892,800

  595,000

  297,800


The data in Table 5 and Figure 1 show that the grain yield of the chemical (positive control) treatment was highest of all. However, the yield on the treatment of ducks + 50% of the N fertilizer (DUN/2) was only 8% less.  According to Mai Van Quyen (1996) the yield of rice grains on fields fertilized with 100 kg of N per hectare reached 85% of the yield compared with 200 kg of N which is consistent with the results of this trial. It would therefore appear that most of the small reduction in rice yield between the positive control and ducks + 50% N was due to the reduction in fertilizer application.  From this it can be concluded that the ducks were extremely effective in controlling pests.  Similarly, it seems reasonable to conclude that the 50% reduction in rice yields on the treatment with ducks only compared to the first two treatments was due almost entirely to a lack of nutrients. This implies that the effect of the manure from the ducks is probably rather small, and that the tripling of yield for the ducks only (DU O) treatment compared to the negative control (neither ducks nor chemicals) was probably mainly due to the ability of the ducks to control pests rather than the effect of manure fertilization.

wpe11.jpg (12096 bytes) wpe12.jpg (14339 bytes)

Performance of the ducks in the duck-rice farming system

When scavenging freely in the rice field the ducks did not need any special management inputs. They preferred to scavenge, and only consumed the supplements available very occasionally. Mortality on all treatments was zero, probably because the plots were protected by the nylon sheets. The growth performance results were very satisfactory and giving the ducks access to a supplement and allowing then to forage freely obviously enabled them to meet their nutrient requirements (Table 6).

Table 6. Performance of local ducklings scavenging in rice fields and with access to a supplement of broken rice and fish meal

DU+N/2

DU O

Probability

Live weight, g
Initial
Removal
Finish
Daily gain, g
Feed conversion, g feed/g liveweight gain


161
953
1313
20.6

3.43


164
941
1300
20.3

3.62


0.633
0.680
0.696
0.617

0.766

The data in Table 6 show that the ducklings grew well when scavenging in the young rice. The good results from scavenging probably were due to the consumption by the ducks of weeds and insects thus providing a varied dietary nutrient intake that was better balanced than that from the supplement alone.

The data for variable costs and benefits for the different treatments are shown in Table 7 and illustrated in Figure 2.

Table 7.   Estimates* of variable costs and benefits (VND/ha) of the integrated duckling-growing rice system compared with chemical control or none (13,000 VND=1US$)

Income from ducks

Cost for ducks

Benefit from ducks

Income from rice

Cost for rice

Benefit from rice

Total benefits

CtrP

0

0

0

7,630,000

4,000,000

3,630,000

3,630,000

DU+N/2

6,932,200

5,626,600

1,305,600

6,998,400

2,945,000

4,055,000

5,360,600

DU O

6,864,000

5,847,500

1,016,500

3,916,800

2,610,000

1,306,800

2,323,300

CtrN

0

0

0

   892,800

   595,000

   297,800

   297,800

* Based on prices per (VND/kg )for broken rice 1600, rice bran 1400, dried fish meal 5000, rice grains 1800, live weight of ducks.

Local farmers can easily raise and manage 500 local ducklings per hectare of growing rice to control pests and weeds. This system works well because the ducks have good distinct characteristics, such as an ability to forage for their foods all the time, even at night, are resistant to diseases and are able to live together in their flock. Also, they can consume many kinds of local feed, especially water plants and small aquatic creatures, far more efficiently than any other animal species. Including ducks in an integrated ducklings-growing rice system, without any use of pesticides, and reducing the recommended amount of chemical fertilizer by 50% nitrogen gives total benefits some 48% higher than those from conventional rice systems using agricultural chemicals. Even by using only ducklings during the growing stage of the rice, and without chemicals, the benefits reached 64% of those from the conventional system. Growing rice without either chemicals or ducks gave a very low economic return.

Conclusion

From the results of the integrated rice-ducks farming experiment we can see that using local ducklings even in the early brooding stage onwards dramatically reduced damage to the rice caused by insect pests and weeds during the early period of the spring-summer crop of directly-seeded, high-yielding rice. It was confirmed that local ducks, due to their strong instinctive scavenging nature can find a high proportion of their own food, almost eliminate damage from insect pests and weeds and in addition produce meat efficiently. When foraging, the ducks don't need to be housed and managed and, in addition to controlling pests, their manure supplies nutrients for growth of the rice plants. This enables the farmers to reduce or eliminate the use of agricultural chemicals, especially pesticides and herbicides, over-use of which can cause health problems for humans and pollute the local environment. The ducks not only are producers of meat and eggs but also help to decrease investments in farming rice, thus increasing net economic benefits and creating jobs for the surplus labour force in the rural areas. Applying this biological control strategy contributes knowledge and understanding of the duck-rice integrated production system in the Mekong Delta.


Acknowledgements

This study was carried out on a smallholding in Phuocthoi village, Cantho province, Vietnam in 1998. It was supported by a grant from the Swedish International Development Authority (SIDA). The authors would like to thank Cantho University for allowing us to carry out the study, our assistant, Phuong and farmers, Ba Ton and Nam Bong for their valuable help.


References

Kim P V 1984 Insect pests on rice production in the Mekong Delta. Dongthap Publisher. pp 5-80.

Mai Van Quyen 1996 Intensive farming of rice production in Vietnam. Agricultural Publisher. 156p.

Nyarko K M and De Datta S  K 1991 A hand book for weed control in rice. International Rice Research Institute. Manila, Philippines. 113 pp.

Received 3 March 1999

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