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Golden apple snail: The dangerous pest on rice


Golden apple snail: The dangerous pest on rice



Common names: Golden snail (English), Golden apple snail (English), Channeled applesnail (English), Apple snail (English), Gelbe Apfelschnecke (German), Golden kuhol (English-Philippines), Miracle snail (English-Philippines).
Scientific name: Pomacea canaliculata (Lamarck, 1819)
Synonyms: Ampullaria canaliculata Lamarck, 1822

Classification


Kingdom:
Animalia
Phylum:
Mollusca
Class:
Gastropoda
(unranked):
clade Caenogastropoda
informal group Architaenioglossa
Superfamily:
Ampullarioidea
Family:
Ampullariidae
Genus:
Pomacea
Subgenus:
Pomacea
Species:
Pomacea canaliculata (Lamarck, 1819)

The Family of apple snails (Ampullariidae J. E. Gray, 1824) has 105-170 freshwater species with 9 genera  and more than 150 nominal species. The Synonyms of this family is Pilidae.
This family consists of two subfamilies (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005), that used classification by Berthold (1991):
-Tribe Ampullariini Gray, 1824 - synonyms: Pilidae Preston, 1915 (inv.); Lanistimae Starobogatov, 1983; Pomaceinae Starobogatov, 1983.
-Tribe Sauleini Berthold, 1991.
There are 9 extant genera in the family Ampullariidae:
+Tribe Ampullariini Gray
Ampullaria , Pila, Lanistes, Pomacea.
+Tribe Sauleini: Saulea , Asolene, Felipponea,  Marisa , Pomella .
The Golden apple snail Pomacea canaliculata is classified under the canaliculata  complex. This is a groups of very closely related species which are very variable in size and appearance.
The relative species:
-Pomacea diffusa.
-Pomacea paludosa.
-Pomacea patula catemacensis Baker
-Pomacea maculata, raremy makes its way

Origin and distribution of the golden apple snails (GAS)

The GAS Pomacea canaliculata is widely distributed in the lentic habitats throughout the Amazon Inferior Basin and the Plata Basin: Southeast Brazil, Argentina, Bolivia, Paraguay and Uruguay. GAS Pomacea canaliculata is one of the most Southern America occuring.
Pomacea canaliculata is a species of large freshwater snail with gills and an operculum, an aquatic gastropod mollusk in the family Ampullariidae, the apple snails.
Native range: temperate Argentina northwards to the Amazon basin. 
The native distribution of  P.canaliculata is basically tropical and subtropical, including Argentina, Bolivia, Paraguay, Uruguay, and Brazil. The southernmost record for the species is Paso de las Piedras reservoir, south of the Buenos Aires province, Argentina.
Non-indigennous distribution
This species also occurs in the United States, where the initial introductions were probably from aquarium release, aka "aquarium dumping". The non-indigenous distribution includes: Langan Park and Three Mile Creek in Mobile, Alabama; a pond bordering the Mobile-Tensaw River Delta in Baldwin County, Alabama ; Little Wekiva River, Orlando, Florida; a lake near Jacksonville, Florida; Lake Mirimar in San Diego County, California; a pond near Yuma, Arizona; and numerous locations in Hawaii. Established populations exist in California and Hawaii.
Introduced range:
Last decades GAS Pomacea canaliculata has spread to South-East Asia and can now be found in Indonesia, Thailand, Vietnam, Cambodia, Hong Kong, southern China, Japan and the Philippines. The snail also invaded in the Southern parts of the USA (Texas and Florida, upto central Ohio) and is expected to spread futher in the comming years. Possibly the species is making its way to Australia too. 
Most of southern, eastern and south-east Asia, including the Philippines, Japan, Taiwan, Vietnam, Cambodia, Thailand, Laos, Korea, Sri Lanka, parts of Indonesia and Malaysia, southern China, Singapore; also Hawai‘i, Guam, and Papua New Guinea; the Dominican Republic; the USA (Florida, Texas, California).
The species has been found in China since 1981. Its initial point of distribution in China was Zhongshan city.
Pomacea canaliculata is also a very common in the aquarium trade, but its voracious appetite gives the GAS family in general a bad reputation in the aquarium hobby. 
Genera Pomacea are New World genera (native to South America, Central America, the West Indies and the Southern U.S.A.).The genera Afropomus, Lanistes, and Saulea are found in Africa.The genus Pila is native to both Africa and Asia.

Description

-Organism type: mollusc
Pomacea canaliculata is a freshwater snail with a voracious appetite for water plants including lotus, water chestnut, taro and rice. Introduced widely from its native South America by the aquarium trade and as a source of human food, it is a major crop pest in south east Asia (primarily in rice) and Hawaii (taro) and poses a serious threat to many wetlands around the world through potential habitat modification and competition with native species.
-Body: The colour of the body varies from yellow (cultivated), brown to nearly black, with yellow spots on the siphon, but not as much on the mouth as in. When at rest, the tentacles are curled under the shell.
-Shell description
The shells of these apple snails are globular in shape. Normal coloration typically includes bands of brown, black, and yellowish-tan; color patterns are extremely variable. Albino and gold color variations exist.
The size of the shell can be up to 75  mm in length.
The shell of this apple snail species is globose and relatively heavy (especially in older snails). The 5 to 6 whorls are separated by a deep, indented suture (hence the name 'canaliculata' or 'channeled'). The shell opening (aperture) is large and oval to round. Males are known to have a rounder aperture than females. The umbilicus is large and deep. The overal shell shape is similar to that of Pomacea lineata, except the deeper sutures and more globose shape in canaliculata. 
The size of these snails varies from 40 to 60 mm wide and 45 to 75 mm high depending on the conditions. 
The colour varies completely yellow and green (cultivated forms) to brown with or without dark spiral bands (wild form). The shell growth of this species occurs mainly in spring and summer, while it stagnates in fall and winter.
Large (up to 7 cm), more or less globular freshwater snails. Aquarium trade snails are often smaller. Shell colour generally brownish or greenish, often with spiral banding patterns around the whorls. Some aquarium bred animals are bright golden yellow. Body colour can vary from dark, almost black to pale cream. Their presence is often first noted by observation of their bright pink egg masses laid on solid surfaces up to about 50cm above the water surface.
-Operculum: The operculum is moderately thick and corneous. The structure is concentric with the nucleus near the centre of the shell. The colour varies light (in young snails) to dark brown. The operculum can be retracted in the aperture (shell opening).  
-Eggs: The reddish (due to the high carotenoid content) eggs are loosely attached to each other. They are attached on object above the waterline and their size varies from 2.20 to 3.5 mm (0.09 to 0.14 inch) diameter. An average clutch contains 200 to 600 eggs.
Pomacea canaliculata depositing the eggs on a trunk.
Eggs of the non-native Pomacea canaliculata on a rock at the border of the Kranji Reservoir, Singapore (12/9/2000).
Note that the bright orange colour is hidden by the dry surface.
Pomacea canaliculata is more likely to eat your plants, which makes it less suitable for most aquaria. These snails also come in different shell and body colours.
Life cycle of the golden apple snails (GAS)
+Adult
This species, unlike most snails known to common people, is not androgynous but gonochoristic. It means it has males and females! GAS P. canaliculata is sexual mature at the size of 2.5 cm/1 inch. Sexes are separate.
-Females lay clusters of bright pink eggs attached to solid surfaces (rocks, walls, logs, emergent vegetation, trash) up to usually about 50cm above the water surface. Females are mostly larger while males have a wider aperture (shell opening).
Many apple GAS deposit the eggs above the waterline in a calcareous clutch. This remarkably strategy of these aquatic snails protect their eggs against predation by fish and other water inhabitants. The apple snail genera Pomacea and Pila, is the tubular siphon at their left side, used to breathe air while they stay submerged, thus making them less vulnerable to snail eating birds. 
The reproductive rate of this snail varies with the temperature and partly by the availability of food. During fall and winter, the reproduction rate is at its lowest point, while with the raising temperatures in spring their reproduction rate increases. 
There are more ways to determine the snail's sex, not all of them are 100% sure. At a temperature of 25oC (77oF/298oK), breeding is at maximum rate.
Reproductive output can be enormous. Clutch size is up to 1000, but averages probably 200-300. Clutches are laid every few weeks.
-Eggs:The female lays its eggs above the water surface at a clutch containing about 200-600 eggs.These eggs will hatch within about 2-3 weeks, depending on temperature an humidity of the air (the air above the water surface should have high humidity)- thus, a glass cover on the tank is essential (water level should be about 5-7.5cm/2-3inch below the glass cover).
Eggs generally hatch within 10-20 days, but may take longer, probably depending on ambient temperature regime. In temperate climates the egg-laying period of this species extends from early spring to early fall while in tropical areas reproduction is continuous. The duration of the reproductive period of P. canaliculata decreases with latitude, to a minimum of six months in the southern limit of its natural distribution.
-The young snails are about 2.5mm (0.09inch) after hatching and immediately start eating; they will also need a constant supply of calcium (both in water and by food). Keeping the young snails with the adults might become a problem after a while, due to competition over food and calcium,so it is advisable to grow them separately. The young snails get to sexual maturity at the size of about 2.5cm (1inch).
Longevity is up to 4 years. Reproductive maturity is reached in 3 months to 2 years, depending on ambient temperature regime.

Habitat

             Breathing

The Golden Apple Snail is amphibious. While there is a sufficient level of dissolved oxygen in the water, they will hardly leave the water and will breathe by their gills. If the level of dissolved oxygen gets to low, the snails will go up to the surface and breathe with their lung (mostly by using its siphon, a tube that it extracts to the water surface). While filling their lung with air, the snails extract and contract their body, so that the pressure differences cause their lung to deplete and refill.

            Feeding habits of the golden snails (GAS)

GAS Pomacea canaliculata is extremely polyphagous, feeding on vegetal (primarily macrophytophagous, feeding on floating or submersed higher plants), detrital, and animal matter. Diet may vary with age, with younger smaller individuals feeding on algae and detritus, and older, bigger (15mm and above) individuals later shifting to higher plants.
In captivity, as well as eating vegetables and fish food pellets, GAS will also eat other foods if they are available.
They will sometimes eat brine shrimps and other frozen foods, or dead fish and insects. Generally, they will also eat any of the microscopic vegetation that grow on the tank rocks or walls. Snails will climb out of the water to reach food that is above the waterline. Because of their ability to do this they have become a nuisance in Asia, where they feed on crops.
This species negatively impacts rice and taro agriculture worldwide where it has been introduced. This species lives in freshwater habitat.
A highly generalist and voracious macrophytophagous herbivore. Most plants are eaten, though it does show some preferences, for instance in Hawai‘i it will not eat water hyacinth.
Eats almost all types of plants. As this snail is fast growing, it needs calcium rich water, so it can grow with a healthy shell - the calcium is used as calcium - carbonate to create the shell, lack of calcium will cause the shell to be thinner and more susceptible to breaking and eventually, the snail will die.
Ecology for the golden apple snails (GAS)

The GAS are amphibious animals; They are widely distributed in lakes, ponds and swamps throughout its native range of the Amazon Inferior Basin and the Plata Basin. These amphibious animal remains submerged during the day, hidden in vegetation near the surface. They are more active during the night, and leave the water in search for fresh vegetation. When it is night time, the GAS becomes active and engages in behaviors relating to feeding, as well as mating and laying eggs.
The GAS are exceptionally well adapted to tropical regions characterized by periods of drought alternating with periods of high rainfall. This adaptation is reflected in their life style; they are moderately amphibious. They have an operculum which enables the snail to seal the shell entrance to prevent drying out while they are buried in the mud during dry periods.
In captivity, GAS are most active at night. During the day they usually retreat to somewhere shaded. In an aquarium that is well lit, the exterior of the shell of apple snails may grow filamentous green algae. This is one possible source of food for juvenile snails.
The activity rate of this snail varies highly with the water temperature. At 18°C they hardly move around, this in contrast with higher temperatures e.g. 25°C.
PH should be in range of 6.5-7.5, best at 7.
Water hardness (GH and KH) isn't significant.
Water contain HEAVY METALS are lethal to the snails!
Pomacea canaliculata is more resistant to lower temperatures than most other snails from the genus Pomacea .

The golden apple snail (GAS) is a dangerous rice pest in Asia

The GAS Pomacea canaliculata (Lamarck) is a recently introduced rice pest in Asia. The planting method greatly influences the period of susceptibility to snail damage: wetbed-transplanted 20-day-old seedlings were less damaged than dapog-transplanted 13-day-old seedlings or direct-seeded rice.
Seedlings 30 days old were more tolerant of snail damage than younger seedlings.
The GAS Pomacea canalicualata was originally introduced from South America to south-east Asia around 1980s, as a local food resource and as a potential gourmet export item. The markets never developed; the snails escaped or were released, and P. canaliculata became a serious pest of rice throughout many countries of south-east Asia.
The GAS now is a major rice exotic invasive pest in Asia. The yield loss caused by P. canaliculata in rice was estimated varying from 5 % to 100 % depending on locality and the level of infestation in most Asian countries. In China, GAS was first introduced into Guangdong province of China in 1981 and became a serious pest of rice since 1984.
In the Philippines, it is considered the number one rice pest and has caused huge economic lossesDuring the 1980's the introduced snails rapidly spread to IndonesiaThailandCambodia, Hong Kong, southern ChinaJapan and the Philippines and there are indications that they are currently invading Australia. Nevertheless, apple snails are considered a delicacy in several regions and they are often sold in Oriental markets for consumption.
 In the 1980's, GAS Pomacea canaliculata was introduced in Taiwan to start an escargot industry. Such food culture can provided protein for the local population, especially useful for the farmers, who primary live on a rice diet, low in proteins. However, the snails didn't become a culinary success. It also became quickly clear that the imported species were able to transfer the Angiostrongylus cantonensis (rat lungworm) parasite just like the native apple snail population (Pila).However, the snails did not become a culinary success.
It was introduced to Hawai‘i in 1989, probably from the Philippines, and for the same reasons as for its initial introduction to south-east Asia.
Already, introduced P. canaliculata has been implicated in the decline of native species of Pila apple snails in south-east Asia. Also, native species of Pila in the Philippines are reported to have declined as a result of extensive pesticide applications against introduced P. canaliculata.
This parasite spends a part of its life cycle in apple snails and can infect humans when the snail isn't cooked long enough before consumption.  Instead of becoming a food source they escaped, and became a serious pest, posing a real threat to the rice production and the environment. 
Instead of becoming a valuable food source, the introduced snails escaped and became a serious threat to rice production and the native ecosystems. During the 1980s the introduced snails rapidly spread to Indonesia, Thailand, Cambodia, Hong Kong, southern China, Japan and the Philippines.
In 1989 GAS Pomacea canaliculata was introduced in Hawaii to serve as a food source and aquarium pet. Some snails escaped to the wild and turned into a serious pest in the taro and rice fields. Although a few restaurants serve them, the apple snail didn't become a great gastronomic success here either.
Recent research reveals the catastrophic nature of the Pomacea invasion in new habitats: the snail herbivory drastically alters the state and function of invaded natural wetlands. When the plants are consumed, nutrients in the system are shunted to phytoplankton instead of the plants which creates dense algal blooms (Carlsson et al in press. 2004). 
In China, GAS was first introduced into Guangdong province in 1981 and became a serious pest of rice since 1984 (Halwart, 1994). The first record for GAS infestation on rice and Zizania latifolia in Yuyao City of Zhejiang province was found in 2002, and became a serious pest in rice and Z. latifolia fields in 2004 (Pan et al., 2008). 
Z. latifolia, is one of the most important aquatic and economic vegetable crops cultivated in the Southeast China since ancient time (Guo, 2007). Nowadays, around 100 thousands hectares of Z. latifolia were planted in more than ten provinces in China (Chen, 1991; Zhai et al., 2001).
The yield loss caused by GAS in rice was estimated varying from 5 % to 100 % depending on locality and the level of infestation in most Asian countries (Halwart, 1994; Naylor, 1996).
Numerous measures have been taken to control GAS, in Z. latifolia fields. The molluscicide was usually used to kill GAS with a serious environmental and human health consequence, and the hand-picking was proved to be a time-consuming work (Yu et al., 2001; Chen et al., 2003). Thus, local farmers did not adopt these methods extensively for GAS control.
Recently, the biological control was applied to suppress the occurrence of GAS by releasing biological agents such as fishes and ducks in crop fields. However, due to the low efficiency of fishes and ducks, especially for controlling the adult GAS (Yoshie and Yusa, 2008), the Chinese soft-shelled turtle (Pelodiscus sinensis), was tentatively selected as a new biological agent to control GAS in Z. latifolia field (Zheng et al., 2005). 
P. sinensis is widely distributed in Eastern Asia and usually take up 4 ~ 6 years to reach sexual maturity adulthood. P. sinensis consumes insect larvae, small fish, small aquatic animals and seeds of marsh plants (Nuangsaeng and Boonyaratapalin, 2001). Furthermore, P. sinensis is of high commercial value and is commonly cultured in Malaysia, Indonesia and China for food consumption (Jia et al., 2005). The objective of this study is to quantify the role of P. sinensis in biologically controlling GAS in Z. latifolia field.

Human uses from Golden apple snails (GAS)

Use as a human food item

In Veracruz, Mexico, there is a subspecies of apple snail known as P.patula catemacensis Baker, 1922. This subspecies is endemic to Lake Catemaco. This large snail is locally known as "tegogolo" and is prized as a food item.
In Northeast Thailand these snails are collected and consumed. They are picked by hand or with a handnet from canals, swamps, ponds and flooded rice paddy fields during the rainy season. During the dry season when these snails are concealed under dried mud, collectors use a spade to scrape the mud in order to find them. The snails are usually collected by women and children. After collection, the snails are cleaned and parboiled. They are then taken out of their shells, cut, and cleaned in salted water. After rinsing with water, they are mixed with roasted rice, dried chili, lime juice, and fish sauce, and then eaten.
Note! Parasites in Golden apple snails
In China and Southeast Asia, consumption of raw or undercooked snails of Pomacea canaliculata and other snails is the primary route of infection with Angiostrongylus cantonensis causing angiostrongyliasis.
This parasite can infect humans if snails are eaten that have not been thoroughly cooked first. Approximately 1.0 % of the Pomacea canaliculata on sale on local markets in Dali City, Yunnan, China were found to be infected with Angiostrongylus cantonensis in 2009.

Use as a common aquarium animal

In the 1980s, GAS Pomacea canaliculata was introduced in Taiwan to start an escargot industry. It was thought that such food culture could provide valuable proteins for farmers, who primarily live on a rice diet. However, the snails did not become a culinary success.
Hawaii experienced the same introduction of Pomacea for culinary purposes, and its taro industry is now suffering because of it.
The common GAS is Pomacea canaliculata; this snail is more likely to eat aquatic plants, which makes it less suitable for most aquaria. This species can also have different shell and body colours.
This species is considered to be in the top 100 of the "World's Worst Invasive Alien Species".

Use as a bio-control agent

Pomacea and Marisa species have been introduced to Africa and Asia in an attempt to control other medically problematic snails in the family Planorbidae: Bulinus species and Biophalaria species, which serve as intermediate hosts for trematoda parasites. These parasites can cause swimmers itch and schistosomiasis, a disease that affects over 200 million people in tropical regions. One of the species introduced as bio-agent is Marisa cornuarietis; this snail competes with other snails and also directly preys on other species.

Management of golden apple snails (GAS) in wetland rice 

Preventative measures

The primary management approach must be prevention. Strict quarantine must be enforced to prevent introduction and spread. Incipient invasions must be eradicated rapidly while it is still possible to do this. For rice and taro fields, it is preferable to use plants from areas that are known to be apple snail free.
If that's not possible, examine the plants and make sure that there are no apple snails or other unwanted snails and also check for egg clutches. The use of a screen on water inlets helps to retard the spread of apple snails. Screens should be cleaned regularly to obstruction. Around rice and taro fields, a barrier of copper could be used to slow the snail spreading to some extent. Copper is toxic to snails and they do not cross this material. The copper wire or strip should be placed above the water level, on the border of the field.

Control

Eradication of established populations is probably not possible. Numerous measures have been tried in attempts to control GAS in agricultural settings. These include: widespread use of pesticides, with serious environmental and human health consequences; biological control, notably the use of fish and ducks; a range of cultural and mechanical control measures. None has proven entirely effective, safe, and economically viable. None is likely to be appropriate in natural ecosystems.
In rice and taro fields, hand picking is a successful method to control GAS populations without harming the environment. The disadvantage is that it only works when done on regular base. The best results are obtained if the hand picking is done as a community effort. All visible snails should be collected with a scoop net or by hand. After collection the snails can be used for human consumption (beware of parasites!), crushed to serve as a food source for fish or destroyed otherwise.
Eggs should not be forgotten during collection! Baited traps filled with lettuce, cassava and taro leaves can be used to attract the snails and to facilitate the collection. All vegetation and obstacles around fields should be removed as much as possible as the snails need this to deposit their eggs. When there are no suitable eggs-laying sites available, the snails are forced to deposit the eggs on the bare ground where the eggs are very vulnerable and easily fall into the water, which drowns the eggs. Before draining a field, make shallow trenches so that the snails will congregate in the trenches and can be captured easily.
This species has been nominated as among 100 of the "World's Worst" invaders.

Biological control of golden apple snails (GAS)

Biological control of GAS Pomacea canaliculata by Chinese soft-shelled turtle, Pelodiscus sinensis in the wild rice, Zizania latifolia field
Source: Shengzhang Dong; Guowan Zheng; Xiaoping Yu; Changhuan Fu
The wild rice, Zizania latifolia Turcz, used to be one of the important aquatic vegetables cultivated in China. Recently, the GAS Pomacea canaliculata (Lamarck) was found to be a major invasive pest attacking Z. latifolia. To control efficiently GAS, predation by the Chinese soft-shelled turtles (Pelodiscus sinensis) on GAS was evaluated in laboratory and field trials. P. sinensis had a strong predatory capacity and selectivity for GAS both in laboratory and field conditions. All the sizes of P. sinensis prefer to capture smaller snails.
The optimum number of P. sinensis released in Z. latifolia field was dependent on the density of over-wintered GAS, and varied between 30 and 50 turtles per 666.7 m2. The number of GAS declined in the fields with turtles as compared to turtle-free field. A pattern of releasing P. sinensis in Z. latifolia fields was developed and widely adopted by farmers because of much more benefit besides biologically controlling GAS.
This feeding behavior was also found in common carp Cyprinuscarpio (Teo, 2006). It is concluded that P. sinensis is one of the most hopeful biological agents for GAS because they not only prey the young snails, but also attack the adult ones efficiently.
To control GAS, several effective predators have been introduced into agricultural ecosystem, including various ducks and fishes (Teo, 2001; 2006). Domestic ducks were proven effective for biological control of young GAS in paddy field and could prey equally well under low and high pest population densities (Cowie, 2002).
In conclusion, both laboratory trials and field survey results showed that using P. sinensis biologically to control GAS was recommended as an optimal method in wild rice fields infected by GAS.

Control of Golden Apple Snails (GAS) by Tillage and Crop Rotation Techniques

Tillage
Tillage and soil puddling crush snails. The effect varies depending on the snail size and soil hardness. Tillage has greater effects on larger snails. Ten to 40% of GAS smaller than 20 mm are killed by tillage, while 40-90% mortalities are attained with GAS bigger than 20 mm. GAS mortalities are 14-20% higher when soil is compacted (hard) after rice harvest than when soil is friable (soft) after the harvest of wheat (winter crop with no irrigation).
Deep cultivation is not necessary because 80% of GAS are found within 6 cm depth of soil. Higher mortalities are attained by intensive tillage, where a field with compacted soil is tilled shallow with a faster cultivator rotation, resulting in smaller cultivation pitch. Puddling using a paddy harrow is also effective. A field experiment revealed that when the average GAS size was 21 mm, GAS density was reduced by 40% after puddling. Thus, tillage and puddling are good methods for decreasing GAS density before growing of paddy crops.
Crop Rotation
Crop rotation is a practical way to significantly reduce GAS density in a paddy field in Japan. Rice-soybean rotation as a summer crop is common in south Japan. After growing soybean in the previous summer, GAS densities in paddy fields are always very low before rice planting, although GAS are usually not eradicated. No paddy fields after soybean have been found above the tentative control threshold in direct-sown rice (0.5 GAS/m2). Thus, without extra control measures, farmers carry out direct seeding of rice as well as transplanting where seedlings are more tolerable than sprouts. Besides soybean, rotation with other upland crops or vegetables is also effective. Extremely low GAS density before growing paddy crops is attained by tillage and desiccation during upland crop cultivation and low temperature during winter in temperate countries. In the tropics, climatic conditions and crop cycles are different, thus, the effects of crop rotation should be evaluated in such areas

Drainage immobilizes snails.

More preventative measures should be undertaken in high-risk (>/2 snails m than in low-risk 2 snails m -z) fields. Snails can be controlled in low-risk fields by employing one or two cultural methods.
Dapog or direct-seeded methods would benefit from drainage and mechanical control (hand-picking).

Using molluscicide at low dosage

If cultural methods cannot be carried out, snails can be controlled with molluscicide at low dosage. High-risk fields, on the other hand, should be protected with a combination of cultural and mechanical methods. These methods can be substituted with low or high dosages of molluscicide. Molluscicide alone, however, requires a dosage of (1.5 kg a.i. ha which most farmers cannot afford.
References

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