GOLDEN APPLE SNAIL SITUATION AND INTEGRATED MANAGEMENT ACTIVITIES IN SOUTH VIET NAM

Nguyen Huu Huan1 and Ravindra C. Joshi2

1 Vice Director General, Department of Plant Protection, Ministry of Agriculture and Rural Development, Ho Chi Minh City, Viet Nam
2 Senior Research Fellow, Philippine Rice Research Institute (PhilRice), Maligaya, Muñoz Science City, Nueva Ecija 3119, Philippines
E-mail: ppdsouth@hcm.fpt.vn; rcjoshi@philrice.gov.ph; joshiraviph@yahoo.com

Introduction

The Golden Apple Snail (GAS), Pomacea canaliculata (Lamarck), is an important pest of irrigated rice in Viet Nam, especially on the direct-seeded rice in the Mekong Delta. Since 1988 some Vietnamese farmers introduced GAS from Taiwan and Philippines, because of its fast growth, high protein content, and good taste and ease of rearing. Two years later, there were 2 private entrepreneurs (one of them in Ho Chi Minh City and the other one in Kien Giang Province) engaged in large scale snail farming involved farm organizations to promote and sell GAS to other countries. Until 1993, through FAO office in Viet Nam, we were aware of the damage of GAS. The alarming state of GAS infestation became more vivid through out a workshop on the GAS management, which was organized in Tien Giang Province, South Vietnam. The Prime Minister of Vietnamese Government released Decree No. 528/TTg, date September 29, 1994 on GAS prevention, control programs and it was banned raising and transportation.

From September, 1994 to June, 1995 we assessed the distribution of GAS between rice and non-rice habitats and carried out control in whole country, we found out that it appeared in most of provinces. Total funds for GAS control were 2,079 million VND. GAS and its eggmasses destroyed were about 689 tons and 102 tons, respectively.

Today, the average rice area infested annually by GAS in the South Viet Nam is around 80,000 ha. This pest is difficult to control and it spreads everywhere even in the canals of communities.

This report presents information on status of GAS and the effective control measures in the South Viet Nam.

GAS Outbreaks in Recent Years

Based on the survey results made by Plant Protection Department in 1995, the GAS had been spread to all provinces in the whole country (61 / 61 provinces). Infested areas includes 22,717 ha of rice, 460 ha of water morning glory (Ipomoea aquatica) ponds and pools, and 1,147 km of community canals.

GAS is causing serious damage on rice, every rice-cropping season. Its attack force rice farmers to re-seed 2-3 times.

According to Matthias Halwart (1994) showed that the approximate distribution of the GAS in rice in the South Viet Nam first observed in1988.

In the past 5 years, there were 3 years (1999, 2000 and 2001) of widespread GAS outbreaks in South Viet Nam. The GAS population and the infested area (including rice and non-rice habitats) were usually much higher and larger than before 1999 (Table 1 & 2). The floods in the Mekong Delta probably explain this.

Although, the geographical distribution of the GAS is in all provinces in the south
of Viet Nam, but the provinces which grow rice with available irrigation suffer most from GAS damage. In many waterways in the southwestern part of Ho Chi Minh City GAS occurs much more abundantly and frequently than in other northeastern part.

On the other hand, the translocation movement of the GAS during flooding time
(July to October) from one province to another province is very clearly in the Mekong Delta.

Table 1. Infested Rice area by GAS in Past Five Years, South Viet Nam.

Table 2. Volumes of GAS and its Eggmasses Caught in the Yearly Campaigns.

Current Activities of GAS Management

Today, the GAS infestation in the South Viet Nam is known to public and private sectors. Thus, individuals acting alone cannot manage GAS through integrated management system. It is best if groups of farmers’ act together to help establish such a system to obtain stable yield or reduce cost of GAS control.

Generally, with funds coming from Government or local Government for basic research or extension; the technicians of Sub-Department of Plant Protection or Extension Agency in provincial levels do GAS management. Their efforts include research, farmer training by many methods such as “talk and chalk”, panels, leaflets, TV, radio, etc. On the other hand, leaders of local Government organize yearly campaigns on “community GAS control” by soldiers, students, and a large of farmers to reduce GAS populations in community waterways by handpicking method.

Results of Researches

Ecology

According to Kim Cuc (1991), the GAS has gills and a lung-like breathing organ.
Thus, it could life in wetland or upland habitat inspite of even low oxygen conditions (0.3 mg O2 per liter).

GAS is a botanical polyphagous animal; when female GAS grow up at 3 gram
weight (around 30 day-old) or more they can mate and lay eggs. The female GAS crawls out of the water level to lay eggmasses which are bright pink (each eggmass has 10-500 eggs). The female GAS once finished mating, separate out of male. After 8-10 days of mating the female lays eggs. It is possible that sperms of male can still alive in female body until 8-10 days after mating.

The increase in weight of GAS depends on the stages, water temperature, rearing conditions, food for feeding, fecundity etc. However, in the pond conditions the juvenile GAS (<1gr/GAS) and adults (5-10 gr./GAS) can increase weight at 0.035-0.065 gr./day/GAS and 0.330-0.700 gr./day/GAS, respectively.

Figure 1 showed that females reach maturity and took them into the productivity where at first 10 days an average number of egg masses around 3 per female with 3-4 day intervals/egg mass; most of egg masses were laid at the first month. There was decrease of number of egg masses after 30-90 days.

Attractiveness of some Botanical Leaves on GAS
(Source: Le Duc Dong, 1998).

Attractiveness of botanical leaves to GAS was replicated thrice and tested in ponds sized 350m2. In future, baiting with botanical leaves (Table 3) would help to trap GAS in community waterways and thus facilitate easy GAS collection and minimize environmental toxicity.

Table 3. Attractiveness capacity of some botanical leaves to GAS.

Note:
Means followed by a common letter are not significantly different at the 5% level by DMRT.
DAT: Day after treated.

Effect of some pesticides on mortality of GAS.

Effect of some pesticides on mortality of GAS was carried out with 3 replications, using randomized complete block design (RCBD). Each plot measured 1m2 with 50 rice hills and 15 GAS (3.5-cm shell height). Bayluscide 250EC (niclosamide) at rate 0.12ml/m2 resulted over 99% mortality at 5, 7, 10 and 14 days after treatment application. Plots treated with Padan 95% WP at rate 0.12g/ m2 also exhibited high GAS mortality (>99%) at 10 and 14 days after treatment application. The remaining pesticides caused low levels of mortalities (Table 4).

Table 4. Effect of some pesticides on mortality of GAS.

Note:
Means followed by a common letter are not significantly different at the 5% level by DMRT.
DAT: Day after treated.

Effect of some botanical pesticides on mortality of GAS.

Botanical pesticides were tested for their toxicity to GAS (Table 5). The Rotex 5%WP (Rotenone from Derris) (30kg/ha) resulted in 73% and 86% GAS mortalities at 5 and 7 days after treatment application, respectively. While the rest of treatments were less lethal to GAS.

Farmer Training & IPM

In order to guide the farmers manage GAS in the rice fields, plant protection network in Viet Nam in different locations yearly conduct “community IPM”. Current activities on the management of the GAS includes:

• Dissemination of information on GAS damage to farmers. This is done through TV, local radio, extension bulletins, leaflets, and farmer field schools.
• Hand picking and destroying egg masses and adults with social community.
• Recommend farmers to change from direct-seeded to transplanted method in areas where high GAS population and its serious damage in rice cropping season is noticed. While ducks feeds upon small GAS, the big-sized GAS could be fed to fish or shrimp after chopping.
• Construction of shallow canals around the rice fields attracts GAS to water logged areas and thus makes GAS collection easier.
• Pasturing of ducks in rice fields before transplanting is recommended to reduce GAS population.
• Placing bamboo sticks in the canals or around the field and helps to collect egg masses.
• Installation of screen wires (or plastic nets) at irrigation inlets prevent GAS entry into rice fields with water flow.
• Molluscicide application may be necessary once all methods prove futile.

Difficulties/Limitations in GAS Management

• Public and private sectors and most farmers wait for government to initiate control programs. It makes GAS prevention difficult every year in Mekong Delta once there is flooding, as GAS population explodes.
• Biocontrol is not high effectiveness since ducks can not feed on the egg masses or large-sized GAS adults. Botanical pesticides are not commercially available, which makes their use limited and difficult.
• Those individuals that act alone fail to have satisfactory GAS control, but farmer groups still do collaborative actions together.
• Changing from rice direct-seeded culture to transplanting is laborious and costly. Farmers still apply pesticide with high toxicity such as Thiodan (endosulfan) when GAS density is high in high water levels in rice fields.
• So far, with regard to GAS and its impact on the rice ecosystem, IPM still lacks the collaboration of national and international scientist researchers. This can best be done in future with an interdisciplinary approach including national and international researchers help farmers to stop GAS from spreading and manage them especially in direct-seeded rice culture.

References

• Kim Cuc, L. T., Mai Van Dung and N. M. Hoa. 1991. Study on physiology & ecology and mass rearing methods of the Golden Apple Snail. 16 pp.
• Le Duc Dong. 1998. Golden Apple Snail and the first results of its control methods. Presentation at the International Workshop on Golden Apple Snail Management in Rice. August, 1998 in Nghe An province, Vietnam. 11pp.
• Management of the Golden Apple Snail in Rice production in Asia, 16-19 June, 1997 Phisanulok, Thailand.
• Matthias Halwart. 1994. The Golden Apple Snail Pomacea canaliculata in Asian rice farming systems: present impact and future threat. International Journal of Pest Management, 40(2): 199-206.
• PPD, 1995. Paper presented in The International Workshop on Ecology & Management of Golden Apple Snail in Rice production in Asia, June 1997, Phisanulok, Thailand.
  

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